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: Electromagnet

c) It disappears.
[Solution Description]
An electromagnet works on the principle of the magnetic effect of electric current. When current flows through the wire wound around a magnetic material (like iron), it creates a magnetic field, making the material behave like a magnet. However, once the current is turned off, the magnetic field ceases to exist, and the material loses its magnetic property.

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: 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: 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: Applications of Electromagnets

b) Wristwatch.
[Solution Description]
Electromagnets are used in electric bells, motors, fans, loudspeakers, and lifting heavy iron objects like in scrap yard cranes. A wristwatch typically uses permanent magnets or quartz mechanisms, not electromagnets.

Key Concept: Electromagnet Properties

b) Color of the wire used.
[Solution Description]
The strength of an electromagnet depends on: (1) Number of turns in the coil, (2) Amount of current flowing, and (3) Presence of an iron core. The color of the wire is irrelevant to its magnetic strength.

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

c) The compass needle deflects when current flows and returns to its original position when current stops
[Solution Description]
The compass needle deflects due to the magnetic field generated by the current-carrying wire, as discovered by Hans Christian Oersted. When the current flows, the magnetic field is produced, 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

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 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 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: 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: Magnetic Effect of Electric Current

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
A compass needle deflects when it is placed near a current-carrying wire because electric current produces a magnetic field around the wire. The compass needle is a tiny magnet, so it interacts with this magnetic field and changes its direction. Therefore, Assertion (A) is true, Reason (R) is also true, and Reason (R) correctly explains Assertion (A).

Key Concept: Deflection observation

b) Needle deflection doubles
[Solution Description]
Magnetic field strength is directly proportional to current ($B \propto I$). Doubling the current doubles the magnetic field strength. Since compass deflection depends on field strength, the deflection angle increases (but not exactly double as it's a vector addition with Earth's 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: 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: 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: 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: Electromagnet Functionality

c) The magnetic field disappears when the current stops
[Solution Description]
An electromagnet only exhibits magnetic properties when electric current flows through the coil. When the circuit is opened, the current stops flowing, and the magnetic field disappears. Consequently, the iron paper clips are no longer attracted to the electromagnet and fall off.

Key Concept: Factors Affecting Electromagnet Strength

c) Increasing the number of turns in the coil.
[Solution Description]
The strength of an electromagnet depends on the amount of current flowing through the coil and the number of turns in the coil. Increasing either the current or the number of turns strengthens the magnetic field. Using an iron core also enhances the magnetic effect.

Key Concept: Lifting Electromagnets, Applications

c) To increase the magnetic field strength
[Solution Description]
Iron cores enhance the magnetic field produced by the current-carrying coil, making the electromagnet stronger. This allows it to lift heavier metal objects efficiently. Without the iron core, the magnetic field would be weaker, reducing its lifting capacity.

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: 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: 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: Lifting Electromagnets

c) The coil behaves like a strong electromagnet
[Solution Description]
When an electric current flows through a coil, it creates a magnetic field around the coil. If an iron core is inserted into the coil, the magnetic field becomes much stronger because the iron enhances the magnetic effect. As a result, the electromagnet can lift heavier objects. When the current is turned OFF, the magnetic field disappears.

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: 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: 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 passes through a conductor like nichrome wire, the resistance offered by the wire causes some electrical energy to be converted into heat energy. This is why the wire feels warm when current flows through it. The assertion (A) correctly states that the nichrome wire gets heated during this process. The reason (R) explains that nichrome has high resistance, which is the correct explanation for why the wire heats up. Therefore, both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Key Concept: Concept: Factors Affecting Heat Generation

d) Increasing the resistance of the wire by making it thinner
[Solution Description]
The heat generated ($H$) in a wire depends on current ($I$), resistance ($R$), and time ($t$) according to Joule’s law: $H = I^2 R t$. Increasing the resistance (thinner or longer wire), increasing current, or passing current for a longer duration increases heat. Therefore, using a thinner wire increases resistance and thus heat production.

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) Color of the wire
[Solution Description]
The heat generated in a wire depends on the material, thickness, length, duration of current flow, and magnitude of the current. The color of the wire does not affect the heating effect.

Key Concept: Household applications of heating effect

d) Electric fan
[Solution Description]
Household appliances like electric irons, water heaters, and hair dryers use the heating effect of electric current to function. However, an electric fan works on the principle of converting electrical energy into mechanical energy to rotate the blades, not primarily for heating.

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

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The heating effect of electric current occurs due to the resistance offered by the conductor. According to the syllabus, nichrome wire offers higher resistance than copper wire of the same size and length. When the same current is passed, the heat produced ($H$) is given by $H = I^2 R t$, where $I$ is current, $R$ is resistance, and $t$ is time. Since nichrome has higher resistance, it produces more heat compared to copper for the same current and duration. Therefore, both Assertion (A) and Reason (R) are true, and Reason correctly explains Assertion.

Key Concept: Magnetic + Heating effects

c) Both heating and magnetic effects
[Solution Description]
Current produces both magnetic field (deflecting compass) and heating effect (due to resistance). Both phenomena occur simultaneously when current flows.

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: Effect of Resistance on Heating

b) Nichrome wire because it has higher resistance
[Solution Description]
The heat generated in a conductor depends on its resistance for a given current. Since nichrome has higher resistivity than copper, it offers more resistance to the current flow, leading to greater heat generation as per Joule's law of heating $H = I^2Rt$. Therefore, the nichrome wire will get hotter.

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 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: Factors affecting heat generation

c) Color of the wire insulation.
[Solution Description
The amount of heat generated in a current-carrying wire depends on the material (resistivity), thickness (cross-sectional area), length of the wire, and the duration of current flow. However, the color of the wire insulation does not affect the heat generated.

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: Comparison of heating with more cells

c) Heating increases due to higher current
[Solution Description]
Increasing the number of cells increases the voltage, which results in higher current flow for the same resistance. Since heat generated ($H = I^2 R t$) depends on the square of current, the heating effect becomes more pronounced.

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: Factors Affecting Heat Generation

d) The color of the wire
[Solution Description]
The heat generated in a wire due to electric current depends on the material's resistivity, length, cross-sectional area, current magnitude, and time. However, the color of the wire does not influence the heat generation process.

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: 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: 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: 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: Voltaic Cell, Electrolyte, Rechargeable Batteries

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
In a Voltaic cell, electricity is generated through a chemical reaction between the electrodes and the electrolyte. When the chemicals (reactants) are fully consumed, the reaction stops, and no more electrons are transferred, halting the current flow. Thus, Assertion (A) is true. The Reason (R) correctly explains that the current flow depends on this chemical reaction, making it the correct explanation for Assertion (A). Therefore, both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Key Concept: Voltaic cell, Electrolyte

c) Zinc oxidizes to form zinc ions in the electrolyte
[Solution Description]
In a voltaic cell, the metal at the negative electrode (anode) undergoes oxidation, losing electrons and dissolving into the electrolyte. Here, zinc acts as the anode since it is more reactive than copper. The chemical reaction at the anode is: $Zn \rightarrow Zn^{2+} + 2e^-$. The loss of mass occurs because zinc ions ($Zn^{2+}$) dissolve into the lemon juice electrolyte.

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: Function of Electrolyte

c) To allow ion movement for chemical reactions
[Solution Description]
The electrolyte in a Voltaic cell is a conducting liquid (such as a salt solution or weak acid) that allows ions to move between the electrodes, facilitating the chemical reaction that produces electricity.

Key Concept: Chemical Reaction in Voltaic Cell

c) $\text{Zn (s) + Cu}^{2+}\text{(aq)} \rightarrow \text{Zn}^{2+}\text{(aq) + Cu (s)}$
[Solution Description]
In a Voltaic cell with zinc (\text{Zn}) and copper (\text{Cu}) electrodes, the reaction is: $\text{Zn (s) + Cu}^{2+}\text{(aq)} \rightarrow \text{Zn}^{2+}\text{(aq) + Cu (s)}$. Here, zinc oxidizes to $\text{Zn}^{2+}$ while $\text{Cu}^{2+}$ reduces to copper metal.

Key Concept: Chemical reaction in Voltaic cell

c) The cell stops generating electricity
[Solution Description]
In a Voltaic cell, the electric current is generated due to the chemical reaction between the electrodes and the electrolyte. Over time, the chemicals (electrodes or electrolyte) get used up, leading to the termination of the electrochemical reaction.
As a result, the cell stops producing electricity and becomes a 'dead' cell. Thus, no further current flows through the circuit.

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, Rechargeable batteries

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
Assertion (A) is true because in a dry cell, the zinc container oxidizes (loses electrons) to form zinc ions, making it the negative terminal. Reason (R) is also true because the carbon rod gains electrons from the electrolyte, acting as the positive terminal. However, Reason (R) does not explain why the zinc container is the negative terminal—it merely describes the role of the carbon rod. Thus, both are true but Reason is not the correct explanation for Assertion.

Key Concept: Function of Electrolyte in Dry Cell

b) Its electrolyte is a thick moist paste
[Solution Description]
A dry cell is called 'dry' because it does not contain a liquid electrolyte. Instead, it uses a thick moist paste as the electrolyte, making it less prone to leakage compared to a Voltaic cell.

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: Environmental Impact

b) It reduces the need for mining new materials and prevents environmental harm.
[Solution Description]
Rechargeable batteries contain harmful materials like acids and metals (e.g., lead, cadmium, lithium) that can pollute the environment if improperly disposed of. Recycling helps recover valuable materials and prevents environmental damage.

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: 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: Battery recycling, environmental impact

c) Recovers valuable metals and reduces mining demand
[Solution Description]
Lithium-ion batteries contain valuable materials like lithium and cobalt that can be recovered through recycling. This reduces the need for new mining operations, which are environmentally destructive. While preventing fires and reducing landfill waste are benefits, the primary environmental advantage is resource recovery because mining these materials has severe ecological impacts including habitat destruction, water pollution, and high carbon emissions from extraction processes.

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: 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: 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

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
A Voltaic cell produces electricity due to redox reactions occurring between the electrodes and the electrolyte. The electrolyte facilitates the movement of ions, which is essential for maintaining charge balance and allowing current to flow in the external circuit. Thus, both Assertion and Reason are true, and the Reason correctly explains the Assertion.

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 a dry cell cannot be recharged due to irreversible reactions, which is correct. The Reason explains this irreversibility by stating the zinc container gets consumed, which is also true and directly explains why recharging is impossible. Both are correct, and Reason justifies Assertion.

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: 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: 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: Features of Dry Cells

c) They are portable and do not leak due to the paste-like electrolyte.
[Solution Description]
Dry cells are portable, lightweight, and leak-proof due to their paste-like electrolyte. They do not require maintenance and are widely used in small electronic devices like flashlights and remote controls.

Key Concept: Chemical Reaction in Dry Cell

c) Zinc loses electrons to form zinc ions.
[Solution Description]
At the zinc electrode, oxidation occurs where zinc loses electrons to form zinc ions. The reaction is: $Zn \rightarrow Zn^{2+} + 2e^-$. This confirms that zinc acts as the negative terminal by releasing electrons.

Key Concept: Working principle of dry cells

b) Zinc container
[Solution Description]
The negative terminal of a dry cell is made of a zinc container. This is a fundamental characteristic of dry cells as per the syllabus.

Key Concept: Working Principle, Structure of Dry Cells

c) The potential difference drops to zero as the chemical reaction halts.
[Solution Description]
The zinc container acts as the negative terminal in a dry cell. When it corrodes completely, the chemical reaction stops because there is no more zinc to act as the anode. This means no more electrons are released, and the potential difference drops to zero.

Key Concept: Voltaic Cell Operation, Dead Cell

d) The chemical reactants are exhausted, stopping the redox reactions.
[Solution Description]
A Voltaic cell becomes "dead" when:
1. The reactant chemicals (electrodes or electrolyte) are fully consumed in the redox reactions.
2. For example, if zinc is entirely oxidized to $Zn^{2+}$ or the electrolyte’s $H^+$ ions are depleted, the reaction stops.
3. No further electron flow occurs, and the cell cannot supply electricity.
4. This is irreversible unless the reactants are replenished (e.g., replacing electrodes or electrolyte).

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: 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: Electrode Materials, Lemon Cell Experiment

c) Lemon juice acts as an electrolyte; LED glows due to electron flow from iron to copper.
[Solution Description]
In the lemon cell experiment:
1. The lemon juice acts as the electrolyte, enabling the flow of ions between the electrodes.
2. Copper (less reactive) acts as the cathode, and iron (more reactive) acts as the anode. Iron loses electrons: $Fe \rightarrow Fe^{2+} + 2e^-$.
3. The electrons flow through the external circuit (LED) to the copper electrode, generating current.
4. The LED glows only when its positive terminal is connected to the copper electrode and the negative terminal to the iron electrode, ensuring correct current direction.

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: 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: Medical applications, Battery limitations

c) They provide higher energy density and longer lifespan.
[Solution Description]
Lithium batteries offer higher energy density (more energy per unit mass), longer lifespan, and stable voltage output, which is critical for medical devices. Traditional voltaic cells (e.g., zinc-carbon) deplete faster and may leak harmful chemicals, making them unsuitable for implants.

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: 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: Dry cell construction, Electrochemical reactions

c) The cell would produce much lower voltage
[Solution Description]
The zinc container in a dry cell serves as both the negative terminal and participates in the oxidation reaction ($\text{Zn} \rightarrow \text{Zn}^{2+} + 2\text{e}^-$). If replaced with less reactive copper (which has higher reduction potential than zinc), the electrochemical potential difference between electrodes would decrease significantly. This would result in much lower voltage output because the redox reaction becomes less favorable. The carbon rod (positive electrode) requires a more reactive metal (like zinc) to maintain proper cell function.

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: 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: 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: 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: 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: Battery Safety

c) To prevent environmental harm
[Solution Description]
Used batteries may contain harmful materials like acids and metals (lead, cadmium, nickel, or lithium). Proper disposal through e-waste recycling facilities prevents environmental harm and reduces pollution.

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: Rechargeable Battery Lifespan

b) Chemical reactions cause permanent changes in electrode materials
[Solution Description]
Rechargeable batteries degrade over time due to chemical reactions that cause irreversible changes in the electrode materials and electrolyte. Each cycle causes minor structural damage, reducing capacity gradually.

Key Concept: Lithium-ion Batteries

b) They have higher energy density than most alternatives
[Solution Description]
Lithium-ion batteries have higher energy density, meaning they can store more energy per unit weight than many other rechargeable batteries. This makes them ideal for portable devices.

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: 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.

Key Concept: Lithium-ion batteries, recycling

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion states that lithium-ion batteries contain valuable materials like lithium and cobalt, which aligns with the syllabus mentioning these metals are mined and processed in limited parts of the world. Hence, recycling them for reuse is economically sound. The Reason highlights the environmental benefit of recycling these batteries by preventing leakage of harmful substances, which is also emphasized in the syllabus. Moreover, the syllabus explicitly mentions that improper disposal of batteries can lead to environmental hazards due to their toxic components. The Reason correctly explains why the Assertion is important, making it a valid explanation.

Key Concept: Lithium-ion Batteries

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that lithium-ion batteries are widely used in modern electronic devices due to their high energy density, which is true as mentioned in the syllabus. The reason provided is that high energy density allows these batteries to store more energy per unit mass, which is also true and correctly explains why lithium-ion batteries are preferred in electronic devices.