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

c) The needle will deflect in the opposite direction with the same magnitude
[Solution Description]
When the current direction is reversed, the direction of the magnetic field around the wire also reverses (right-hand rule). The compass needle, which aligns with the net magnetic field (Earth's field + wire's field), will now deflect in the opposite direction but with the same magnitude, assuming all other conditions remain unchanged.

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 an electric current flowing through a wire deflects a nearby compass needle, which is true as observed in Activity 4.1 where the compass needle deflected when the circuit was closed. The reason given is that a current-carrying conductor produces a magnetic field around it, which is also true and correctly explains why the compass needle gets deflected. The magnetic field generated by the current interacts with the compass needle's magnetic field, causing deflection. Thus, both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Key Concept: Applications of Electromagnetism

c) Electromagnet
[Solution Description]
Devices such as electromagnets, electric motors, and loudspeakers use the principle of the magnetic effect of electric current. These devices rely on the interaction between the magnetic field produced by the current and permanent magnets or other magnetic materials to function.

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: Disappearance of Magnetic Field

b) When the current stops flowing.
[Solution Description]
The magnetic field around a current-carrying wire exists only as long as the current flows through the wire. When the current stops, the magnetic field disappears.

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: Oersted's Experiment

d) Hans Christian Oersted
[Solution Description]
Hans Christian Oersted discovered in 1820 that an electric current produces a magnetic field. He observed that a compass needle deflected when an electric circuit was closed or opened, proving the connection between electricity and magnetism.

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: Magnetic field around a current-carrying wire

c) Due to the magnetic field created by the electric current in the wire
[Solution Description]
The current-carrying wire produces a magnetic field around it, which exerts a force on the magnetic compass needle, causing it to deflect. This is because the compass needle aligns itself along the direction of the resultant magnetic field, which includes both Earth's magnetic field and the wire's magnetic field.

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

c) Electric current produces a magnetic field around the conductor.
[Solution Description]
Oersted discovered that an electric current produces a magnetic field around the conductor carrying it. This was observed when a compass needle deflected near a current-carrying wire. His discovery established the link between electricity and magnetism, leading to further studies in electromagnetism.

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 placed near a current-carrying wire. This is true because, as observed in experiments, the current flowing through the wire creates a magnetic field around it. The reason explains that an electric current produces a magnetic field around the conductor. This is also true and directly explains why the compass needle deflects—the magnetic field of the current-carrying wire interacts with the magnetic needle. Hence, both are true, and the reason correctly explains 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 of current, Compass needle deflection

b) Towards west
[Solution Description]
The magnetic field due to the current-carrying wire can be determined using the right-hand thumb rule. If the current flows from north to south, the magnetic field lines around the wire are clockwise when viewed from the south. Since the compass needle was initially pointing towards geographic north, the north pole of the compass needle will be deflected towards the west.

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: 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 when an electric current flows through a conductor, the compass needle deflects. This is true because a current-carrying conductor produces a magnetic field (as observed in Activity 4.1). The reason explains that this deflection happens due to the magnetic field created by the current-carrying conductor, which aligns with Oersted’s discovery. Hence, both the assertion and reason are correct, and the reason correctly explains the assertion.

Key Concept: Magnetic Effect of Current

c) The iron nail enhances the magnetic field strength
[Solution Description]
Inserting an iron nail increases the magnetic permeability of the core, making the magnetic field stronger. The iron core acts as a magnet itself, amplifying the overall magnetic effect of the coil, leading to greater deflection of the compass needle.

Key Concept: Magnetic poles of electromagnets

c) By observing which compass pole is attracted to the electromagnet's end
[Solution Description]
To determine the polarity of an electromagnet using a compass, place the compass near one end of the electromagnet while the current is flowing. If the north pole of the compass needle is attracted to that end, then that end is the south pole of the electromagnet (since unlike poles attract). Similarly, the other end will be the north pole.

Key Concept: Polarity of Electromagnets, Current Direction

d) The North and South poles switch places
[Solution Description]
The polarity of an electromagnet is determined by the direction of current flow through the coil. Reversing the current direction reverses the magnetic poles of the electromagnet (North becomes South and vice versa), as per the right-hand rule.

Key Concept: Electromagnets

c) The nail behaves like a magnet and attracts iron clips
[Solution Description]
When an electric current is passed through a coil wound around an iron nail, the nail behaves like a magnet and attracts magnetic materials such as iron clips. This is because the current-carrying coil generates a magnetic field, which magnetizes the iron nail. When the current is turned off, the nail loses its magnetism.

Key Concept: Electromagnet Polarity

b) End A is the south pole
[Solution Description]
According to the principle of magnetism, unlike poles attract each other. If the north pole of the compass is attracted towards end A of the electromagnet, then end A must be the south pole. This is because opposite poles (North and South) attract each other.

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: Electromagnets, Polarity

c) The compass needle's south pole points towards the nail
[Solution Description]
The polarity of an electromagnet reverses when the direction of the current is reversed. Initially, the north pole of the compass points towards the nail, meaning the nail's end was a south pole. Reversing the current will switch the poles; hence, the compass's south pole will now point towards the nail.

Key Concept: Electromagnets and Magnetic Poles

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
When electric current flows through the coil of an electromagnet, it generates a magnetic field, making it behave like a magnet. This is why the electromagnet can attract iron clips. However, when the current is switched off, the magnetic field ceases to exist, and the electromagnet no longer exhibits magnetic properties. Therefore, both Assertion and Reason are true, and the Reason correctly explains the Assertion.

Key Concept: Factors affecting electromagnet strength, Current effect

c) Student Y's electromagnet will be stronger
[Solution Description]
The strength of an electromagnet increases with the number of turns in the coil because more turns create a stronger magnetic field for the same current. Since both students use the same cell (same current), Student Y’s coil with twice the number of turns will produce a stronger magnetic field than Student X’s, resulting in greater deflection of a compass needle or attracting more iron clips.

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: Electromagnet polarity, Magnetic effect of current

c) End A is a north pole
[Solution Description]
The compass needle aligns itself according to the magnetic field produced by the coil. Like poles repel each other, so if the north pole of the compass is repelled by end A, it means end A must also be a north pole. This follows the rule that "like poles repel, unlike poles attract."

Key Concept: Lifting electromagnets, Magnetic effect of current

c) Increase the number of cells in the battery
[Solution Description]
To solve this question, recall that the strength of an electromagnet depends on:
1) The amount of electric current in the coil.
2) The number of turns in the coil.
3) The presence of an iron core.
Increasing the number of cells (which increases current), increasing the number of turns in the coil, or using a stronger iron core would make the electromagnet stronger. However, reversing the current direction only changes the polarity, not the strength.

Key Concept: Heating effect of current, Resistance

c) Nichrome wire because it has higher resistance
[Solution Description]
The heating effect of electric current depends on the resistance of the conductor. Nichrome has higher resistance than copper for the same dimensions. According to Joule's law of heating, $H = I^2 R t$, where $H$ is heat produced, $I$ is current, $R$ is resistance, and $t$ is time. Since the voltage source is the same and nichrome has higher resistance, it will dissipate more heat compared to the copper wire.

Key Concept: Practical applications, Safety

c) Nichrome wire has high resistance and a high melting point
[Solution Description]
Nichrome is an alloy with high resistivity, which means it offers high resistance to the flow of current. Due to its high resistance, it heats up quickly and can sustain high temperatures without melting, making it ideal for heating elements. It also has a high melting point and does not oxidize easily at high temperatures.

Key Concept: Heating Effect of Electric Current

b) The wire becomes warm.
[Solution Description]
When an electric current passes through a conductor like a nichrome wire, it gets heated due to the resistance offered by the wire. This is known as the heating effect of electric current. Thus, the wire becomes warm.

Key Concept: Heat Generation with Multiple Cells

c) The wire heats up more.
[Solution Description]
Using a battery of 2 cells increases the voltage, which results in a higher current flowing through the wire. Since the heat generated depends on the magnitude of the current, the wire will heat up more with 2 cells compared to 1 cell for the same duration.

Key Concept: Heating effect, Material resistance

d) Nichrome wire; higher resistance to current flow
[Solution Description]
The heating effect of current depends on the resistance of the material. Nichrome has higher resistivity compared to copper. For the same length and thickness, resistance $R$ is given by $R = \rho \frac{L}{A}$, where $\rho$ is resistivity, $L$ is length, and $A$ is cross-sectional area. Since nichrome has higher $\rho$, it will resist current flow more, converting more electrical energy into heat energy. Thus, the nichrome wire heats up more.

Key Concept: Safety precautions, Wire selection

d) To prevent overheating; wire may melt or cause hazards
[Solution Description]
Thinner wires have higher resistance per unit length (since $R \propto 1/A$, where $A$ is cross-sectional area). For a given current, higher resistance causes more heat generation ($H = I^2 R t$). If the wire is too thin, excessive heat can melt insulation, damage plugs/sockets, or cause fires. Hence, using appropriately rated wires ensures safe heat dissipation.

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: 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: Resistance and 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 a thicker copper wire produces less heat than a thinner nichrome wire for the same current and length. This is true because the heating effect depends on the resistance of the wire ($H = I^2 R t$). Copper has lower resistivity than nichrome, and a thicker wire has lower resistance due to $R = \rho \frac{L}{A}$. The reason correctly explains the assertion since resistance decreases with increasing cross-sectional area ($A$) for the same material and length.

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: Factors Affecting Heating

c) Color of the conductor
[Solution Description]
The heating effect depends on the current (I), resistance (R), and time (t) as per $H = I^2 R t$. The color of the conductor does not influence the heat produced

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: Resistance, Material property comparison

c) Nichrome has higher resistivity and durability at high temperatures
[Solution Description]
Nichrome has higher resistivity ($\rho$) compared to copper. A high-resistivity material like nichrome generates more heat for the same current flow due to greater opposition ($R = \rho \frac{L}{A}$). Additionally, nichrome has a high melting point and does not oxidize easily at high temperatures, making it durable for heating applications.

Key Concept: Heating effect of current, Nichrome wire properties

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
According to Joule's law of heating, the heat produced ($H$) 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 compared to copper, its resistance ($R$) is higher for the same dimensions. Thus, for the same current ($I$) and duration ($t$), more heat is generated in nichrome due to its higher resistance. Therefore, both Assertion (A) and Reason (R) are true, and Reason correctly explains Assertion.

Key Concept: Heating effect of electric current

d) Nichrome wire has higher resistance than copper wire.
[Solution Description]
Nichrome wire is preferred over copper wire for heating devices because it has a higher resistance compared to copper wire of the same dimensions. The higher resistance causes more heat to be generated when current flows through it, making it suitable for heating applications.

Key Concept: Resistance, Material properties, Industrial applications

b) Increases by 50%
[Solution Description]
Resistance ($R$) is given by $R = \rho \frac{L}{A}$, where $\rho$ is resistivity, $L$ is length, and $A$ is area.
Original resistance: $R_1 = \rho \frac{L}{A}$.
New length: $L_2 = L + 0.5L = 1.5L$.
New resistance: $R_2 = \rho \frac{1.5L}{A} = 1.5R_1$.
Thus, resistance increases by 50%.

Key Concept: Energy conversion, Efficiency, Safety

b) 0.3 kWh
[Solution Description]
Total energy consumed per hour = $1500 \text{ W} \times 3600 \text{ s} = 5,400,000 \text{ J}$.
Energy converted to heat = $80\% \times 5,400,000 = 4,320,000 \text{ J}$.
Energy lost = Total energy - Heat energy = $5,400,000 - 4,320,000 = 1,080,000 \text{ J}$.
Converting to kWh: $\frac{1,080,000}{3,600,000} = 0.3 \text{ kWh}$.

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 Electric Current

b) Electric iron
[Solution Description]
Household appliances like electric irons, room heaters, and kettles work based on the heating effect of electric current, where electrical energy is converted to heat energy due to resistance in the conductor.

Key Concept: Voltaic Cell

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
In a Voltaic cell, electricity is generated due to chemical reactions between the electrodes (made of different metals) and the electrolyte (a liquid or paste). The electrolyte facilitates the movement of ions, completing the circuit and allowing the chemical reaction to occur. Thus, both Assertion (A) and Reason (R) are true, and R correctly explains A.

Key Concept: Voltaic Cell and Dry Cell

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion is true as per section 4.3.1 and 4.3.2 - Voltaic cells indeed use a liquid electrolyte, whereas dry cells use a moist paste electrolyte. The Reason is also true, since the absence of liquid in dry cells makes them more portable and less prone to leakage or spillage compared to Voltaic cells. Moreover, the Reason correctly explains why dry cells are more portable, which is directly related to the nature of their electrolyte.

Key Concept: Voltaic Cell Components

c) It facilitates the chemical reaction between the electrodes.
[Solution Description]
The electrolyte in a Voltaic cell facilitates the chemical reaction between the electrodes by allowing ions to move freely, thus enabling the generation of electric current.

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: 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: Voltaic cell

c) Assertion is true, but Reason is false.
[Solution Description]
In a Voltaic cell, two electrodes of different metals are immersed in an electrolyte. Chemical reactions occur at the electrodes, leading to the generation of electricity. The assertion is true. The electrolyte facilitates the movement of ions, not electrons, so the reason is false because it incorrectly states that the electrolyte acts as a medium for electron flow.

Key Concept: Voltaic cell components

d) Two different metal plates with a conducting liquid
[Solution Description]
A Voltaic cell consists of two different metal electrodes and an electrolyte, which can be a weak acid or salt solution. The chemical reaction between these components generates electricity.
Copper and zinc are common electrode materials, while lemon juice or saltwater is used as the electrolyte.
Therefore, both electrodes and an electrolyte are necessary for a functional Voltaic cell.

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: Electrolyte composition, Cell performance

c) Electrolyte modification maintains ion mobility
[Solution Description]
Cold temperatures thicken the electrolyte paste, reducing ion mobility which decreases current output. For proper functioning in cold:
Step 1: Standard electrolyte becomes too viscous, slowing $NH_4^+$ and $Cl^-$ ion movement
Step 2: Modified cells use special low-temperature electrolytes with better fluidity
Step 3: Chemical reaction rates decrease at low temperatures
Step 4: Zinc container properties don't affect cold performance significantly
Solution requires understanding multiple interdependent factors affecting cell operation.

Key Concept: Energy conversion, Disposable vs rechargeable

b) Disposable: \$0.17/h; Rechargeable: \$0.005/h
[Solution Description]
Complex calculation requiring multiple steps:
Step 1: Disposable runtime = $\frac{3000mAh}{500mA} = 6$ hours (\$1 total)
Step 2: Rechargeable per-cycle runtime = $\frac{2000mAh}{500mA} = 4$ hours
Step 3: Total rechargeable lifespan = $4h \times 500 = 2000$ hours (\$10)
Step 4: Cost comparison:
- Disposable: $\frac{\$1}{6h} = \$0.167/h$
- Rechargeable: $\frac{\$10}{2000h} = \$0.005/h$
Must account for both capacity and reusability.

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: Rechargeable Batteries

c) Lithium-ion battery
[Solution Description]
Lithium-ion (Li-ion) batteries are the most common type of rechargeable batteries today. They are used in many devices such as smartphones, laptops, and electric vehicles. Unlike dry cells, they can be recharged 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: Future battery technology

c) Higher energy density and improved safety
[Solution Description]
Solid-state batteries offer three key advantages over liquid electrolyte batteries: 1) They are safer because they eliminate flammable liquid electrolytes that can cause fires. 2) They can potentially store more energy in the same space (higher energy density). 3) They typically have longer lifespans and can withstand more charge cycles. These characteristics would directly improve electric vehicle range (energy density), safety (solid electrolyte), and longevity (cycle life).

Key Concept: Environmental Impact

c) They contain harmful chemicals that pollute the environment
[Solution Description]
Rechargeable batteries contain hazardous materials like acids, lithium, lead, or cadmium, which can cause environmental pollution or fires if improperly disposed of. Many components are also valuable and recyclable, making proper disposal essential.

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 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: Electrode potential, metal pairs in voltaic cells

d) Magnesium and Copper
[Solution Description]
The voltage produced by a voltaic cell depends on the difference in electrode potentials of the two metals. Among the given options, the pair with the largest potential difference will generate the highest voltage. Standard reduction potentials show that magnesium has a much lower (more negative) potential than copper, leading to a higher cell voltage compared to other pairs like zinc/copper or iron/copper.

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 Functioning

c) Copper
[Solution Description]
In a Voltaic cell, copper often acts as the positive electrode due to its chemical properties, while metals like zinc or iron act as the negative electrode.

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, Rechargeable batteries

c) Rechargeable batteries can be reused, reducing waste and cost.
[Solution Description]
Dry cells are single-use and cannot be recharged. Once their chemical reactions deplete the electrolyte, they must be disposed of. Rechargeable batteries can be recharged multiple times by reversing the chemical reaction through an external power source. This makes them cost-effective and environmentally friendly over time, as they reduce waste.
First, identify that dry cells have a limited lifespan due to irreversible chemical reactions. Second, understand that rechargeable batteries allow reversal of chemical reactions when charged. Third, conclude that using rechargeable batteries reduces waste and long-term costs since they can be reused. Hence, replacing a dry cell with a rechargeable battery is beneficial for sustainability and economy.

Key Concept: Dry cell components

c) Zinc container
[Solution Description]
A dry cell consists of a zinc container which acts as the negative terminal and a carbon rod at the center that acts as the positive terminal. The electrolyte is a paste-like substance inside the zinc container.

Key Concept: Rechargeable batteries

c) Lithium-ion battery
[Solution Description]
The lithium-ion (Li-ion) battery is the most common type of rechargeable battery found in almost all modern devices due to its efficiency, rechargeability, and widespread availability.

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: 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: Structure of Dry Cells, Working Principle

c) The gas bubbles increase internal resistance, reducing voltage output.
[Solution Description]
Hydrogen gas forms due to side reactions at the carbon rod (positive terminal). This gas buildup creates resistance, known as polarization, which reduces the efficiency and voltage output of the cell over time.

Key Concept: Working principle of dry cells, Environmental impact of batteries

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
The assertion states that the zinc container acts as the negative terminal due to oxidation, which is correct. Zinc loses electrons (\textit{oxidation}) and forms Zn$^{2+}$ ions, making it the negative terminal. The reason describes the role of the moist paste electrolyte surrounding the carbon rod, which is also true. However, the reason does not explain why zinc is the negative terminal; it explains the electrolyte's function, which is unrelated to the assertion. Thus, both are true, but the reason does not correctly explain the assertion.

Key Concept: Electrolyte in Voltaic cell

b) Weak acid or salt solution[Solution Description]The electrolyte in a Voltaic cell is usually a weak acid or salt solution, such as sulfuric acid or saltwater.

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: 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: Chemical Reaction Stopping Condition

c) When one or both electrodes are fully oxidized/reduced.
[Solution Description]
A Voltaic cell stops generating electricity when the reactants (chemicals involved in the redox reactions at the electrodes) are completely consumed. For instance, if all the zinc in the electrode is converted to $Zn^{2+}$ or hydrogen ions are depleted, the reactions cease, and the cell becomes "dead."

Key Concept: Applications of Voltaic Cells

d) Providing backup power in small electronic gadgets
[Solution Description]
Voltaic cells are widely used in portable devices like torches, remote controls, and small electronic gadgets due to their ability to convert chemical energy into electrical energy.

Key Concept: Voltaic Cell, Rechargeable Batteries

d) Assertion is false, but Reason is true.
[Solution Description]
The Assertion states that rechargeable batteries can be used indefinitely without degradation, which is false because they wear out after repeated charging and discharging cycles as mentioned in the syllabus. The Reason is true because rechargeable batteries indeed rely on reversible chemical reactions to function, allowing them to be recharged. Since the Assertion is false but the Reason is true, the correct answer is d).

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: Chemical Reaction in Voltaic Cells

b) Oxidation of zinc
[Solution Description]
In a voltaic cell, oxidation occurs at the anode. For example, zinc (Zn) loses electrons to form zinc ions ($\text{Zn}^{2+}$), as shown in the reaction:
$\text{Zn (s)} \rightarrow \text{Zn}^{2+} \text{(aq)} + 2e^-$

Key Concept: Construction of dry cells

b) Serves as the negative terminal and undergoes oxidation
[Solution Description]
In a dry cell, the zinc container serves as the anode (negative terminal). It undergoes oxidation, releasing electrons into the external circuit. The chemical reaction at the anode is: $Zn \rightarrow Zn^{2+} + 2e^-$. The zinc container also physically holds the electrolyte paste and other components.

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: 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: Characteristics of Dry Cells

c) They cannot be recharged
[Solution Description]
One of the limitations of dry cells, as per the syllabus, is that they cannot be recharged. Once the reactants are exhausted, the cell becomes 'dead' and must be disposed of.

Key Concept: Battery Basics

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that dry cells are commonly used in flashlights and toys due to their lightweight and portable nature, which is true. The reason explains that dry cells convert chemical energy into electrical energy via redox reactions, which is also correct and directly explains why they are suitable for portable devices like flashlights and toys. Therefore, both the Assertion and Reason are true, and the Reason correctly explains the Assertion.

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: Battery Chemistry, Battery Applications

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
Assertion is true because during the discharge of a dry cell, zinc oxidizes and forms $\text{Zn}^{2+}$ ions, which dissolve into the electrolyte, causing the zinc container to lose mass over time.
Reason is also true because the chemical reaction involves the oxidation of zinc ($\text{Zn} \rightarrow \text{Zn}^{2+} + 2e^{-}$), which is consistent with the assertion.
Additionally, the reason correctly explains why the zinc container loses mass (oxidation leads to dissolution). Thus, both statements are true, and the reason provides the correct explanation.

Key Concept: Rechargeable Batteries

b) They can be recharged and reused multiple times
[Solution Description]
Rechargeable batteries can be reused multiple times by recharging them with electricity, saving money and reducing waste. Unlike single-use dry cells, they do not need frequent replacement, making them ideal for long-term use in devices like mobile phones.

Key Concept: Rechargeable Batteries, Lithium-ion Batteries, Environmental Considerations

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description] The Assertion states that solid-state batteries are safer and charge faster than traditional lithium-ion batteries due to the replacement of liquid electrolytes with solid materials. This is true as solid-state batteries indeed offer enhanced safety and faster charging. The Reason explains that solid-state batteries eliminate the risk of leakage and thermal runaway associated with liquid electrolytes, which is also correct. Moreover, the Reason directly supports the Assertion by providing a specific explanation for why solid-state batteries are safer.
Therefore, both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Key Concept: Working principle of 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 recharged and reused multiple times, which is true as mentioned in the syllabus. The Reason explains this by stating that rechargeable batteries rely on reversible chemical reactions, which is also true and correctly explains why they can be recharged. Thus, both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

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

d) They are safer, charge faster, and last longer
[Solution Description]
Scientists are working on solid-state batteries because they replace liquid or paste-like electrolytes with solid materials, making them safer, faster to charge, and longer-lasting, as mentioned in "A step further" in the syllabus.

Key Concept: Environmental impact of batteries

a) They contain valuable materials and can harm the environment
[Solution Description]
The syllabus mentions that even when a battery stops working, it still contains materials like acids and metals (e.g., lead, cadmium, nickel, or lithium), which can be harmful to the environment if disposed of improperly. Additionally, these materials are valuable and can be recycled and reused. Thus, recycling batteries is good for both the planet and people.

Key Concept: Concept: Recycling Rechargeable Batteries

b) Prevents pollution and allows valuable materials to be reused
[Solution Description]
Recycling rechargeable batteries prevents hazardous materials like lead, cadmium, nickel, or lithium from polluting the environment. It also allows valuable materials to be reused, reducing the need for mining new resources.

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.

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.