Key Concept: Assertion-Reason

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that an electric current produces a magnetic field, which is true as observed in experiments like Oersted's experiment. The reason explains that the deflection of a compass needle near a current-carrying wire confirms this magnetic effect, which is also true and correctly explains the assertion. Both statements are true, and the reason justifies the assertion.

Key Concept: Magnetic effect of electric current, Oersted's experiment

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
When an electric current flows through a wire, it produces a magnetic field around it, as observed in Oersted’s experiment. This magnetic field interacts with the compass needle, causing it to deflect from its original alignment along the Earth's magnetic field. Thus, the Assertion is true. The Reason states that a compass needle naturally aligns with the Earth's magnetic field, which is also correct. However, the Reason does not explain why the needle deflects near the current-carrying wire specifically; it only describes the general behavior of the compass. Therefore, while both statements are true, the Reason does not correctly explain the Assertion.

Key Concept: Magnetic Effect of Electric Current

b) The compass needle deflects from its original direction.
[Solution Description]
When an electric current flows through a conductor, it generates a magnetic field around it. The compass needle is a small magnet that aligns itself along the direction of the magnetic field. Thus, when the current flows, the compass needle deflects due to the magnetic field created by the current-carrying wire. When the circuit is opened and no current flows, the magnetic field disappears, and the compass needle returns to its original position aligned with Earth's magnetic field.

Key Concept: Hans Christian Oersted's Discovery

c) Hans Christian Oersted
[Solution Description]
Hans Christian Oersted was the scientist who observed in 1820 that a compass needle deflected when placed near a current-carrying wire. This discovery established the link between electricity and magnetism, leading to further research in electromagnetism.

Key Concept: Practical Applications, Electromagnets

b) 300 kg
[Solution Description]
First, find the current ($I$) flowing through the electromagnet using Ohm's Law:
$I = \frac{V}{R} = \frac{12}{2} = 6 \text{ A}$
The magnetic field ($B$) is proportional to the current and is given as 0.02 T per kg of iron. Let $m$ be the mass of the iron object. Then:
$B = kmI$
Here, $k$ is the proportionality constant. For $B = 0.02m$ T and $I = 6$ A, we can solve for $m$:
$0.02m = k \times 6 \times m$
Simplifying, $k = \frac{0.02}{6}$.
The maximum magnetic field corresponds to the maximum current (6 A). Thus, the maximum weight that can be lifted is:
$B_{\text{max}} = 0.02m_{\text{max}} \implies m_{\text{max}} = \frac{B_{\text{max}}}{0.02}$
But since $B_{\text{max}} = k \times 6 \times m_{\text{max}}$, substituting back:
$m_{\text{max}} = \frac{(0.02/6) \times 6 \times m_{\text{max}}}{0.02}$
This simplifies to $m_{\text{max}} = 300$ kg.
However, the correct approach involves realizing that the magnetic field must balance the gravitational force per unit mass. Therefore, the correct calculation yields:
$m_{\text{max}} = \frac{B}{0.02} = \frac{0.02 \times 300}{0.02} = 300 \text{ kg}$

Key Concept: Magnetic Effect of Electric Current, Hans Christian Oersted's Experiment

c) Assertion is true, but Reason is false.
[Solution Description]
The assertion states that the deflection of a compass needle when current flows through a wire indicates the production of a magnetic field by the current-carrying wire. This is correct because Oersted's experiment demonstrated that an electric current creates a magnetic field around the conductor, causing the compass needle to deflect. The reason claims that a magnetic field only exists in the presence of a permanent magnet, which is false. Magnetic fields can be produced by both permanent magnets and current-carrying conductors. Therefore, the assertion is true, but the reason is false.

Key Concept: Magnetic Effect of Electric Current

b) The compass needle gets deflected.
[Solution Description]
When electric current flows through a wire, it produces a magnetic field around it. This magnetic field causes the compass needle to deflect from its original position. The deflection occurs because the compass needle is a tiny magnet and interacts with the magnetic field produced by the current-carrying wire.

Key Concept: Magnetic Effect of Electric Current

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that a compass needle deflects when an electric current flows through a nearby wire. This is true because, as discovered by Hans Christian Oersted, an electric current generates a magnetic field around the wire, which interacts with the magnetic compass needle, causing it to deflect. The reason states that an electric current produces a magnetic field around the conductor, which affects the compass needle. This is also true and correctly explains why the compass needle deflects. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Discovery of the magnetic effect of electric current

d) Hans Christian Oersted
[Solution Description]
Hans Christian Oersted discovered that an electric current produces a magnetic field around it when he observed the deflection of a compass needle near a current-carrying wire in 1820.

Key Concept: Oersted's Experiment

d) Hans Christian Oersted
[Solution Description]
Hans Christian Oersted, a Danish scientist, discovered in 1820 that an electric current produces a magnetic field. He observed the deflection of a compass needle when an electric circuit was closed or opened, leading to this discovery.

Key Concept: Magnetic Effect of Current

b) The compass needle deflects from its original direction
[Solution Description]
When electric current flows through a wire, it produces a magnetic field around the wire. This magnetic field interacts with the compass needle (which is a tiny magnet itself), causing deflection. Once the current stops, the magnetic field disappears, and the needle returns to its original position.

Key Concept: Magnetic field around a current-carrying wire

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that a compass needle deflects when placed near a current-carrying wire, which is true because the current generates a magnetic field around the wire (as observed in Oersted's experiment). The reason correctly explains that an electric current produces a magnetic field around it, which is the fundamental principle behind the deflection of the compass needle. Thus, both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Magnetic effect of electric current, Compass needle deflection

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that when current flows through a wire parallel to the compass needle, the needle deflects perpendicular to the wire. This is true because a current-carrying wire produces a circular magnetic field around it as per Ampere's law, and the compass needle aligns itself along the tangent to this circular field, resulting in a perpendicular deflection.
The reason states that the direction of the magnetic field around a current-carrying wire is always perpendicular to the direction of the current flow. This is also true, as determined by the right-hand rule: if the thumb points in the direction of current, the curled fingers indicate the circular magnetic field lines, which are perpendicular to the current.
Moreover, the reason correctly explains the assertion because the perpendicular magnetic field causes the compass needle to deflect perpendicularly to the current-carrying wire.

Key Concept: Magnetic effect and current strength

c) The magnetic field doubles in strength.
[Solution Description]
The magnetic field ($B$) produced by an electric current ($I$) is directly proportional to the current ($B \propto I$). Therefore, if the current is doubled, the magnetic field strength also doubles. This stronger field causes a more pronounced deflection in the compass needle.

Key Concept: Direction of magnetic field, Current reversal

c) Deflects to the west
[Solution Description]
The direction of the magnetic field around a current-carrying wire reverses when the current direction is reversed. If the compass needle initially deflected to the east, reversing the current will cause it to deflect in the opposite direction, i.e., to the west.

Key Concept: Direction of deflection

b) The needle deflects in the opposite direction.
[Solution Description]
The direction of the magnetic field around a current-carrying wire depends on the direction of the current. Reversing the current reverses the polarity of the magnetic field, which causes the compass needle to deflect in the opposite direction compared to its initial deflection.

Key Concept: Electromagnets, Magnetic Poles, Current Direction

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
The assertion states that the polarity of an electromagnet reverses when the direction of the current is reversed. This is true because the magnetic field direction is determined by the right-hand rule, which changes with the current direction. The reason states that the magnetic field depends on the current direction and the number of turns in the coil. While this is true, it does not explain why the polarity reverses; it only explains factors affecting the magnetic field strength. Thus, the assertion is true, but the reason does not correctly explain it.

Key Concept: Factors affecting electromagnet strength

c) Increasing the number of cells (higher current)
[Solution Description]
The strength of an electromagnet can be increased by increasing the number of turns in the coil or by increasing the current passing through the coil. Adding more cells (battery) provides higher current, leading to a stronger magnetic field.

Key Concept: Assertion-Reason

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
According to Activity 4.2, when electric current flows through the coil, the iron nail becomes magnetized and attracts iron clips. When the current stops, the magnetic effect vanishes, and the clips fall down. This confirms that the Assertion is true. The Reason correctly explains why the electromagnet works—it behaves like a magnet only when current flows, which aligns with the observation. Therefore, both Assertion and Reason are true, and Reason correctly explains the Assertion.

Key Concept: Electromagnet Polarity

b) The end is a South pole
[Solution Description]
The compass needle's North pole is attracted to the opposite pole of the electromagnet (South pole). Therefore, if the North pole of the compass points towards the electromagnet, that end must be the South pole.

Key Concept: Strength of Electromagnet

d) Reducing the number of turns in the coil
[Solution Description]
The strength of an electromagnet depends on the current flowing through the coil and the number of turns in the coil. Increasing either of these factors increases the strength. However, reducing the number of turns in the coil decreases the magnetic field strength, as fewer turns result in a weaker magnetic effect.

Key Concept: Electromagnet Basics

c) The coil acts as a magnet only while current flows.
[Solution Description]
When an electric current flows through the coil wound around an iron nail, the coil behaves as a magnet and attracts nearby magnetic materials like iron paper clips. The iron core enhances the magnetic effect. When the current is stopped, the magnetic effect disappears.

Key Concept: Electromagnets

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
In an electromagnet, the magnetic effect is produced due to the flow of electric current through the coil. When the current is switched off, the magnetic field disappears because there is no longer any current flowing to generate it. Therefore, both Assertion and Reason are true, and Reason correctly explains the Assertion.

Key Concept: Polarity of Electromagnet

c) By observing which compass pole is attracted to the coil's end.
[Solution Description]
The polarity of an electromagnet can be determined by placing a magnetic compass near one end of the coil. If the north pole of the compass needle is attracted to that end, it indicates the end is a south pole (since unlike poles attract). Similarly, the other end will have the opposite polarity (north).

Key Concept: Electromagnetism

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
According to the syllabus, lifting electromagnets work on the principle that when electric current flows through a conductor (like a wire), it produces a magnetic field around it. When the current is turned ON, the electromagnet lifts the iron/steel objects; when the current is switched OFF, the magnetic field disappears, and the objects are released. Therefore, the Assertion correctly states that lifting electromagnets lose their magnetic effect when the current is switched OFF, and the Reason accurately explains this phenomenon as the disappearance of the magnetic field due to the stopping of the current.

Key Concept: Strength Control

b) By increasing or decreasing the current
[Solution Description]
The lifting capacity of an electromagnet can be controlled by adjusting the electric current. Increasing the current strengthens the magnetic field, allowing heavier objects to be lifted. Conversely, decreasing the current weakens the magnetic field, reducing the lifting capacity. Turning the current OFF completely removes the magnetic field, releasing any attached objects.

Key Concept: Application

c) In factories and scrap yards for moving metal objects
[Solution Description]
Lifting electromagnets are widely used in factories and scrap yards for moving, lifting, and sorting heavy metal objects efficiently. Their ability to control magnetism via electric current makes them ideal for handling large quantities of metal without physical contact.

Key Concept: Assertion-Reason

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
An electromagnet's strength depends on the magnetic field generated by the current in the coil. When an iron core is inserted, it becomes magnetized due to the current-induced magnetic field, thereby significantly increasing the overall magnetic strength. Thus, both the Assertion and Reason are true, and the Reason correctly explains the Assertion.

Key Concept: Heating Effect of Electric Current

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
When electric current flows through a conductor like nichrome wire, it faces resistance. Due to its high resistance property, nichrome converts more electrical energy into heat energy compared to other conductors like copper. This explains why the wire heats up. Therefore, both Assertion and Reason are true, and Reason correctly explains Assertion.

Key Concept: Concept: Heating Effect of Electric Current

d) Resistance in the wire converts electrical energy into heat energy.
[Solution Description]
When electric current flows through a conductor like nichrome wire, it faces resistance, which causes some electrical energy to be converted into heat. This heating effect occurs due to the material's resistivity. Nichrome has high resistance compared to other conductors, leading to more heat generation when current passes through it. Thus, the wire gets warm.

Key Concept: Resistance and Heating

a) It is a good conductor of electricity and generates more heat.
[Solution Description]
Nichrome wire is preferred in heating devices because it offers high resistance to the flow of electric current. Due to this high resistance, more heat is generated when current passes through it compared to other conductors like copper of the same size and length. It is also a good conductor of electricity, but the primary reason is its high resistance leading to higher heat generation.

Key Concept: Concept: Practical Applications

d) Nichrome has higher resistance and can withstand high temperatures
[Solution Description]
Nichrome has higher resistivity than copper, meaning it offers greater resistance to the flow of current. As a result, it generates more heat per unit of current. Additionally, nichrome does not oxidize easily at high temperatures, making it durable for heating purposes. Copper, being highly conductive, would not heat up sufficiently and might melt under high current.

Key Concept: Factors affecting heat generation

c) The heat produced decreases.
[Solution Description]
The resistance of a wire is directly proportional to its length ($R \propto L$). Doubling the length doubles the resistance ($R_{\text{new}} = 2R$). Since $H = I^2Rt$ and $I = V/R$, doubling the resistance reduces the current by half ($I_{\text{new}} = V/(2R) = I/2$). Substituting these values, the new heat produced becomes $H_{\text{new}} = (I/2)^2(2R)t = (1/2)I^2Rt$, which is half the original heat. Thus, the heat produced decreases.

Key Concept: Heating Effect of Electric Current

b) Because of the conversion of electrical energy into heat energy due to resistance
[Solution Description]
When electric current flows through a conductor, it encounters resistance, which converts some electrical energy into heat energy. This is known as the heating effect of electric current.

Key Concept: Assertion-Reason

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that a nichrome wire gets hot when electric current is passed through it, which is true as nichrome has high resistance leading to the heating effect of electric current. The reason given is also true because high resistance causes electrical energy to be converted into heat energy. Moreover, the reason correctly explains why the assertion occurs. Thus, both assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Heating effect of electric current, Resistance

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The heating effect in a conductor is given by $H = I^2 R t$, where $I$ is current, $R$ is resistance, and $t$ is time. Since nichrome has higher resistivity ($\rho$) than copper, its resistance $R = \rho \frac{L}{A}$ is greater for the same dimensions (length $L$ and cross-sectional area $A$). Thus, for the same current, the heat produced in nichrome is higher due to its higher resistance. Both Assertion and Reason are true, and the Reason correctly explains the Assertion.

Key Concept: Heating effect of electric current

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
When electric current flows through a conductor like nichrome, the resistance of the material causes some electrical energy to be converted into heat energy. This is called the heating effect of electric current. Nichrome has higher resistance than copper, so more heat is generated in nichrome for the same current. Thus, both assertion and reason are true, and the reason correctly explains why the nichrome wire gets hot.

Key Concept: Heating effect of current, Resistance factors

b) Nichrome wire because it has higher resistance
[Solution Description]
The heating effect depends on resistance. Nichrome has higher resistance than copper for the same dimensions. Using $H = I^2Rt$, since current $I$ is same (same battery), nichrome wire generates more heat due to its higher resistance.

Key Concept: Heating effect applications, Safety

b) To prevent overheating and potential fires[Solution Description]Underrated components can overheat due to excessive current, leading to melting/fire. Properly rated components ensure safe operation by handling expected current without overheating, preventing energy loss and hazards.

Key Concept: Resistance and Heating Effect

c) Heat increases
[Solution Description]
The heating effect of electric current increases with the magnitude of the current, as per Joule's law of heating. Heat generated ($H = I^2 R t$) is directly proportional to the square of the current (I). Therefore, increasing the current leads to more heat production.

Key Concept: Practical application of heating effect

b) Electrical energy is converted into heat energy.
[Solution Description]
When an electric current passes through the heating element (usually made of nichrome), the resistance of the wire converts electrical energy into heat energy due to the heating effect of current. This heat is then used to warm the base of the iron.

Key Concept: Heating effect, Nichrome wire properties

b) It doubles
[Solution Description]
The heat produced per second ($H$) in a wire is given by $H = I^2 R t$, where $I$ is current, $R$ is resistance, and $t$ is time. For simplicity, we can consider $t = 1$ second. The resistance of a wire is given by $R = \rho \frac{L}{A}$, where $\rho$ is resistivity, $L$ is length, and $A$ is cross-sectional area. Doubling the length ($L' = 2L$) while keeping the area ($A$) constant increases the resistance to $R' = \rho \frac{2L}{A} = 2R$. Since $H$ is proportional to $R$, the heat produced doubles.

Key Concept: Current, Heat energy relationship

b) It becomes one-fourth
[Solution Description]
The heat produced ($H$) is given by $H = I^2 R t$. Reducing the current to half ($I' = \frac{I}{2}$) affects the heat produced as $H' = (\frac{I}{2})^2 R t = \frac{1}{4} I^2 R t = \frac{H}{4}$. Thus, the heat reduces to one-fourth of the original value when current is halved.

Key Concept: Factors affecting heating in wires

c) Color of the wire[Solution Description]The heat generated in a wire depends on the material (resistivity), length, thickness (cross-sectional area), and current magnitude. The color of the wire does not affect the heating effect.

Key Concept: Heating effect, Resistance, Power

c) Heat produced quadruples
[Solution Description]
The heat produced per second (power) is given by $P = \frac{V^2}{R}$.
Initially, power is $P_1 = \frac{V^2}{R}$.
When voltage is doubled, new power is $P_2 = \frac{(2V)^2}{R} = \frac{4V^2}{R} = 4P_1$.
Thus, the heat produced per second becomes four times the original value.

Key Concept: Heating Effect of Current

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion states that an electric iron gets hot when current passes through its heating element. This is true because appliances like electric irons utilize the heating effect of electric current to generate heat. The Reason states that this heating effect occurs due to the resistance in the conductor, which converts electrical energy into heat energy. This is also true and correctly explains why the assertion holds. Hence, both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Key Concept: Safety Concerns Due to Heating Effect

d) Using wires rated for the specified current and avoiding circuit overloading
[Solution Description]
Overheating in household wiring can be prevented by using wires with appropriate current ratings, ensuring proper insulation, and avoiding overloading circuits. Using thicker wires reduces resistance and minimizes heat generation.

Key Concept: Heating Effect of Electric Current

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that the heating element in an electric iron is made of nichrome wire, which is true because nichrome is commonly used due to its high resistance and ability to produce substantial heat. The reason provided explains why nichrome is suitable for heating elements—its high resistance causes more heat generation when current flows through it, which directly justifies the assertion. Therefore, both statements are true, and the reason correctly explains the assertion.

Key Concept: Dry Cells

a) Voltaic cells use a liquid electrolyte, while dry cells use a paste-like electrolyte.
[Solution Description]
A Voltaic cell uses a liquid electrolyte, whereas a dry cell uses a paste-like electrolyte. Dry cells are more convenient for everyday use due to their non-spillable nature.

Key Concept: Basic Concept

b) Zinc container
[Solution Description]
In a dry cell, the zinc container acts as the negative terminal, while the carbon rod (covered with a metal cap) serves as the positive terminal.

Key Concept: Dry cells, Rechargeable batteries

b) The chemical reactions in dry cells are irreversible
[Solution Description]
Dry cells use an irreversible chemical reaction where the electrolyte (a moist paste) reacts completely with the electrodes, depleting the reactants permanently. The zinc container corrodes, and the manganese dioxide gets reduced, leaving no way to reverse the reaction. In contrast, rechargeable batteries like lithium-ion cells use reversible reactions, allowing the original materials to be restored during recharging.

Key Concept: Rechargeable batteries, Environmental impact

c) Toxic metals can contaminate soil and water
[Solution Description]
Lithium-ion batteries contain toxic metals like lithium and cobalt, which can leak into soil and water if disposed of improperly. These materials are flammable and may cause fires in landfills. Additionally, mining these metals has significant ecological impacts. Recycling is essential to recover valuable materials and prevent environmental contamination.

Key Concept: Electrode Polarity, Chemical Reaction

b) Zinc electrode because it undergoes oxidation
[Solution Description]
Zinc acts as the negative terminal because it is more reactive than copper. In the electrochemical series, zinc has a higher tendency to lose electrons and undergo oxidation compared to copper. When zinc reacts with the acidic lemon juice (electrolyte), it releases electrons that flow through the external circuit to the copper electrode (positive terminal). This electron flow constitutes the electric current.

Key Concept: Multi-Cell Configuration, LED Connection

c) Incorrect polarity of LED connection[Solution Description]The LED might not glow because it is connected in reverse polarity. LEDs are diodes that allow current to pass only in one direction. The longer lead of the LED must be connected to the positive terminal (copper electrode in this case) and the shorter lead to the negative terminal (iron electrode). If connected oppositely, no current flows, and the LED remains off. Reversing the connections should make it glow if all other components are functioning correctly.

Key Concept: Voltaic cell components and function

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
In a lemon cell, the copper and iron electrodes are inserted into the lemon, which contains acidic juice acting as the electrolyte. When these electrodes come into contact with the lemon juice, a chemical reaction occurs where zinc (from the iron nail) loses electrons and copper gains them. This electron flow generates an electric current, producing electricity. Thus, both Assertion (A) and Reason (R) are true, and Reason correctly explains why the lemon cell generates electricity.

Key Concept: Discovery of Voltaic cell

c) Alessandro Volta
[Solution Description]
Alessandro Volta demonstrated that electricity could be generated through chemical reactions, leading to the creation of the first practical battery, known as the Voltaic pile.
Luigi Galvani also contributed to early discoveries in bioelectricity, but it was Volta who invented the first battery based on this principle.

Key Concept: Dry Cells - Structure and Function

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
In a dry cell, the zinc container serves as the negative terminal because it undergoes oxidation (loses electrons) during the chemical reaction that generates electricity. The carbon rod acts as the positive terminal. The reason correctly explains why zinc is used as the negative terminal, as it readily loses electrons due to its position in the electrochemical series.

Key Concept: Electrolyte in Dry Cell

b) Thick moist paste of ammonium chloride and zinc chloride
[Solution Description]
The electrolyte in a dry cell is not a liquid but a thick, moist paste. This is why it is called a 'dry' cell. The paste consists of ammonium chloride and zinc chloride, which facilitate the chemical reaction necessary for electricity generation.

Key Concept: Dry Cells

d) Assertion is false, but Reason is true.
[Solution Description]
The Assertion states that the dry cell is called 'dry' because its electrolyte is a liquid. However, this is false as the dry cell is called 'dry' because its electrolyte is a thick moist paste, not a liquid. The Reason correctly explains why it is called a dry cell by stating that the electrolyte is a thick moist paste and not a liquid. Therefore, the Assertion is false, but the Reason is true.

Key Concept: Rechargeability of Dry Cells

b) Their chemical reactions are irreversible and exhaustible
[Solution Description]
Dry cells are single-use because the chemical reactions that produce electricity are irreversible. Once the reactants are exhausted, the cell cannot be recharged and must be disposed of. Rechargeable batteries use reversible reactions, allowing them to be reused multiple times.

Key Concept: Rechargeable battery economics

b) Rechargeable Li-ion batteries (\$40)
[Solution Description]
Calculate total energy needed: 2000mAh/day × 365 days × 5 years = 3,650,000mAh required.
Single-use batteries:
3,650,000mAh ÷ 1200mAh/battery = 3041.67 → 3042 batteries needed.
Total cost = 3042 × \$0.50 = \$1521.
Rechargeable batteries:
Each battery provides 2000mAh × 500 cycles = 1,000,000mAh over lifetime.
3,650,000mAh ÷ 1,000,000mAh/battery = 3.65 → 4 batteries needed.
Total cost = 4 × \$10 = \$40.
The rechargeable option is far cheaper.

Key Concept: Common Application

c) Lithium-ion batteries
[Solution Description]
Lithium-ion (Li-ion) batteries are widely used in modern devices due to their efficiency, lightweight nature, and ability to hold a charge for extended periods.

Key Concept: Rechargeable batteries, Lithium-ion batteries

d) Assertion is false, but Reason is true.
[Solution Description]
The assertion claims that lithium-ion batteries are common due to easily accessible materials, but this is false because lithium and cobalt are actually scarce and concentrated in few regions, as mentioned in the syllabus. The reason correctly states that these materials are mined in limited parts of the world, which is true according to the syllabus. Thus, the assertion is false, but the reason is true.

Key Concept: Rechargeable Battery Chemistry

a) Graphite
[Solution Description]
Lithium-ion batteries use graphite (carbon) as the anode. During charging, lithium ions move from the cathode to the anode and embed themselves between the layers of graphite. This reversible process allows Li-ion batteries to be rechargeable.

Key Concept: Voltaic Cell Experiment

b) To act as an electrolyte
[Solution Description]
Lemon juice acts as an electrolyte in the lemon battery experiment, facilitating the flow of electric current between the copper and iron electrodes.

Key Concept: Voltaic Cell Components

a) Copper and zinc plates with saltwater as the electrolyte
[Solution Description]
A Voltaic cell requires two electrodes made of different metals and an electrolyte (like lemon juice or salt solution). The correct combination should consist of dissimilar metals and a conductive liquid.

Key Concept: Chemical reactions in voltaic cells, electrode materials

d) The chemicals involved in the reaction get used up
[Solution Description]
A voltaic cell stops working when the chemical reactants (electrodes or electrolyte) are depleted due to the redox reactions occurring at the electrodes. Over time, these reactions consume the active materials, reducing their ability to produce electrons or ions, leading to a depletion of electrical energy. This state is referred to as a "dead" cell.

Key Concept: Voltaic Cell and Electrolyte

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
A Voltaic cell requires an electrolyte, which is a conducting liquid, to facilitate the chemical reaction that generates electricity. The electrolyte allows the movement of ions between the two electrodes (positive and negative), completing the internal circuit. This ion movement is essential for the flow of electric current in the external circuit. Thus, both Assertion (A) and Reason (R) are true, and Reason correctly explains why the electrolyte is necessary in a Voltaic cell.

Key Concept: Dry cells and rechargeable batteries

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that the zinc container acts as the negative terminal in a dry cell because zinc is more reactive than carbon. This is correct since zinc loses electrons more easily (higher reactivity) and serves as the anode (negative terminal). The reason explains the process by which zinc provides electrons through oxidation, which is the correct explanation for why zinc is used as the negative terminal. Thus, both Assertion and Reason are true, and Reason correctly explains the Assertion.

Key Concept: Dry cell structure

c) It acts as the negative terminal
[Solution Description]
The zinc container in a dry cell acts as the negative terminal (anode). During the electrochemical reaction, the zinc undergoes oxidation, releasing electrons that flow through the external circuit to generate electricity.

Key Concept: Chemical reactions, Dry cells

c) It loses electrons and slowly corrodes away.
[Solution Description]
In a dry cell, the zinc container undergoes oxidation (loses electrons) to produce zinc ions ($\text{Zn}^{2+}$). This reaction provides electrons that flow through the external circuit, generating electricity. Over time, the zinc container corrodes as it dissolves into the electrolyte.
Step 1: Zinc reacts with the moist paste electrolyte. Step 2: The oxidation half-reaction occurs at the anode (zinc): $\text{Zn} \rightarrow \text{Zn}^{2+} + 2\text{e}^-$. Step 3: Electrons flow out via the negative terminal, powering devices. Step 4: Zinc gradually degrades as it forms $\text{Zn}^{2+}$ ions. Therefore, the zinc container corrodes while supplying electrons for current.

Key Concept: Dry cells and rechargeable batteries

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
Dry cells are called “dry” because they do not contain a free-flowing liquid electrolyte like wet cells. Instead, the electrolyte is present in the form of a thick moist paste. This paste allows the chemical reaction needed to produce electric current, but it does not spill easily. Therefore, Assertion (A) is true, and Reason (R) correctly explains why dry cells are called dry.

Key Concept: Applications, Rechargeable Batteries

c) Rechargeable batteries reduce long-term costs and environmental impact.
[Solution Description]
Rechargeable batteries can be reused multiple times by recharging, which reduces long-term costs and environmental waste. Dry cells are single-use and would require frequent replacement, making them impractical for high-energy applications like electric vehicles.

Key Concept: Dry cell structure and function

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that the zinc container in a dry cell acts as the negative terminal due to electron donation during the chemical reaction, which is true. The reason explains that zinc's higher reactivity compared to carbon causes it to lose electrons and act as the negative terminal, which is also correct and provides the scientific basis for the assertion. Therefore, both statements are true, and the reason correctly explains the assertion.

Key Concept: Working principle and structure of dry cells

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that the zinc container acts as the negative terminal, which is true as per the given syllabus. The reason explains that this is because the zinc reacts with the electrolyte to release electrons, which is also correct. Moreover, the reason directly explains why the zinc container functions as the negative terminal. Thus, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Function of electrolyte in dry cells

d) To facilitate ion movement for current flow
[Solution Description]
The paste-like substance inside the dry cell acts as the electrolyte, facilitating the flow of electric current by allowing ions to move between the electrodes.

Key Concept: Electrodes in Voltaic cell

c) Electrodes[Solution Description]The two metal plates in a Voltaic cell are called electrodes. One acts as the positive electrode and the other as the negative electrode.

Key Concept: Voltaic Cell Components

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
A Voltaic cell consists of two electrodes and an electrolyte. The electrolyte allows ions to move between the electrodes, enabling a chemical reaction that produces electrical energy. Therefore, the assertion is true. The reason correctly explains the role of the electrolyte in facilitating this reaction, making it the correct explanation of the assertion.

Key Concept: Voltaic Cell Electrodes

b) Acts as the negative terminal and releases electrons.
[Solution Description]
In a Voltaic cell, the zinc electrode undergoes oxidation, losing electrons to form zinc ions ($Zn^{2+}$). The reaction at the zinc electrode is:
$Zn \rightarrow Zn^{2+} + 2e^-$
Therefore, the zinc electrode acts as the negative terminal (anode), supplying electrons to the external circuit.

Key Concept: Function of Voltaic cell

d) To generate electric current through chemical reactions[Solution Description]A Voltaic cell generates electric current due to chemical reactions between the electrodes and the electrolyte.

Key Concept: Portable Power Sources

c) They provide continuous power through spontaneous chemical reactions.
[Solution Description]
Portable devices like flashlights require small, self-contained power sources that can convert chemical energy directly into electrical energy without external input. Voltaic cells fulfill this need by providing a steady current due to spontaneous redox reactions.

Key Concept: Rechargeable Batteries

c) Lithium-ion batteries
[Solution Description]
Rechargeable batteries, such as lithium-ion batteries, are a type of voltaic cell that can be recharged and reused multiple times, making them ideal for devices like mobile phones and laptops.

Key Concept: Applications of Voltaic cells

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that Voltaic cells are used in medical devices like pacemakers, which is true as they provide portable and long-term power. The reason explains that Voltaic cells offer a steady and reliable source of electricity, which is also true and directly supports the assertion since medical implants require consistent power. Hence, the reason correctly explains the assertion.

Key Concept: Redox reactions, Applications of voltaic cells

b) 3,839 C
[Solution Description]
First, calculate the moles of zinc oxidized:
$\text{Moles of Zn} = \frac{\text{Mass}}{\text{Molar Mass}} = \frac{1.30\,\text{g}}{65.38\,\text{g/mol}} \approx 0.0199\,\text{mol}$
The oxidation reaction is:
$\text{Zn (s)} \rightarrow \text{Zn}^{2+} + 2e^-$
From stoichiometry, 1 mole of Zn produces 2 moles of electrons. So, total charge $Q$ is:
$Q = n \times F \times \text{moles of electrons per mole} = 0.0199\,\text{mol} \times 96,485\,\text{C/mol} \times 2 \approx 3,839\,\text{C}$

Key Concept: Working Principle

b) Positive terminal to negative terminal
[Solution Description]
According to the working principle of a dry cell, the current flows from the positive terminal (carbon rod) through the circuit to the negative terminal (zinc container). This is explicitly stated in the syllabus.

Key Concept: Electrolyte in dry cells

d) To prevent leakage and improve portability
[Solution Description]
The electrolyte in a dry cell is a moist paste instead of a liquid to prevent leakage, make the cell portable, and ensure stability during movement or tilting. A liquid electrolyte could spill, causing damage or short circuits. The thick paste maintains conductivity while being safer and more convenient for everyday use.

Key Concept: Chemical reactions in dry cells

b) $2MnO_2 + 2NH_4^+ + 2e^- \rightarrow Mn_2O_3 + 2NH_3 + H_2O$
[Solution Description]
In a zinc-carbon dry cell, the cathode reaction occurs at the carbon rod (positive terminal), where manganese dioxide ($MnO_2$) reacts with ammonium ions ($NH_4^+$) and electrons to form manganese(III) oxide ($Mn_2O_3$), ammonia ($NH_3$), and water ($H_2O$). The correct reaction is: $2MnO_2 + 2NH_4^+ + 2e^- \rightarrow Mn_2O_3 + 2NH_3 + H_2O$

Key Concept: Construction and working of dry cells

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The zinc container serves as the negative terminal (anode) in a dry cell because it undergoes oxidation, losing electrons: $\text{Zn} \rightarrow \text{Zn}^{2+} + 2\text{e}^-$. The reason correctly explains that the zinc container is the negative terminal due to this electrochemical reaction, making both statements true with a valid causal link.

Key Concept: Battery Usage

c) Flashlights[Solution Description]Dry cells are commonly used in small portable devices such as flashlights, toys, remote controls, and wall clocks due to their compact design and convenience for everyday use.

Key Concept: Dry Cell Components

b) Zinc container
[Solution Description]
A dry cell consists of a zinc container that acts as the negative terminal and a carbon rod (covered with a metal cap) as the positive terminal. The electrolyte is a moist paste surrounding the carbon rod.

Key Concept: Battery Usage in Daily Life

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
Dry cells are indeed widely used in flashlights due to their ability to provide portable electrical energy, and they are designed for single-use as the chemical reaction inside them ($\text{Zn} + 2\text{MnO}_2 + 2\text{NH}_4\text{Cl} \rightarrow \text{Zn(NH}_3\text{)}_2\text{Cl}_2 + \text{Mn}_2\text{O}_3 + \text{H}_2\text{O}$) is irreversible. This irreversibility prevents recharging, validating both the Assertion and Reason. Furthermore, the Reason correctly explains why dry cells are single-use, linking the assertion about their usage to the underlying chemical property.

Key Concept: Chemical Reactions, Energy Conversion

c) The chemical reactions in the dry cell have stopped
[Solution Description]
A dry cell generates electricity through chemical reactions. When these reactions are complete, the cell is depleted and can no longer produce electric current, causing the toy car to stop. Unlike rechargeable batteries, dry cells cannot be recharged and must be replaced once used up.

Key Concept: Rechargeable Batteries

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description] The assertion states that rechargeable batteries can be reused multiple times, which is true as they are designed for repeated charging and discharging cycles. The reason explains that this reusability occurs due to the presence of materials enabling reversible chemical reactions, which is also true and directly explains why rechargeable batteries can be reused.

Key Concept: Rechargeable Batteries

d) Lithium-ion (Li-ion)
[Solution Description]
The most common type of rechargeable battery used in devices today is the lithium-ion (Li-ion) battery, as mentioned in the syllabus under "A step further."

Key Concept: Battery Recycling

a) It prevents hazardous materials from contaminating the environment
[Solution Description]
Rechargeable batteries contain hazardous materials like heavy metals that can contaminate soil and water if not disposed properly. Recycling recovers valuable materials while preventing pollution.

Key Concept: Rechargeable batteries, Environmental impact

c) Their materials can cause environmental harm if not recycled properly.
[Solution Description]
The syllabus highlights that lithium-ion batteries contain materials like lithium and cobalt, which are mined in limited parts of the world. These materials can cause environmental harm if not disposed of properly, as they may lead to fires or contaminate the environment. Recycling these batteries is crucial to prevent harm and reuse valuable materials.

Key Concept: Rechargeable batteries, Lithium-ion batteries

d) Solid-electrolyte interface layer formation and electrode degradation
[Solution Description]
Lithium-ion batteries degrade primarily due to the formation of a solid-electrolyte interface (SEI) layer on the anode, which consumes lithium ions and reduces capacity. Additionally, repeated expansion and contraction of electrode materials during charging and discharging cause structural damage, leading to capacity loss over time.

Key Concept: Concept: Future Battery Technologies

c) They replace liquid electrolytes with solid materials
[Solution Description]
Solid-state batteries replace liquid or paste-like electrolytes with solid materials. This makes them safer, capable of faster charging, and longer-lasting compared to traditional lithium-ion batteries.

Key Concept: Concept: Lithium-ion Battery Characteristics

c) Lightweight and ability to recharge multiple times
[Solution Description]
Lithium-ion batteries are popular because they are lightweight, have a high energy density, and can be recharged many times before wearing out. They are commonly used in devices like phones and laptops due to these advantages.

Key Concept: Solid-state batteries, Future battery technology

d) They replace liquid electrolytes with non-flammable solid materials
[Solution Description]
Solid-state batteries replace liquid/paste electrolytes with solid materials, eliminating flammable components that can leak or ignite. This structural change prevents thermal runaway reactions, a major hazard in traditional Li-ion batteries, while enabling higher energy densities and faster charging without compromising safety.