Chapter Exercises Solutions

Questions and Answers

1. Fill in the blanks

(i) The solution used in a Voltaic cell is called electrolyte. (ii) A current carrying coil behaves like a magnet (or electromagnet).

2. Choose the correct option

(i) Dry cells are less portable compared to Voltaic cells. Answer: False (Dry cells are more portable because they use a paste, not liquid).

(ii) A coil becomes an electromagnet only when electric current flows through it. Answer: True

(iii) An electromagnet, using a single cell, attracts more iron paper clips than the same electromagnet with a battery of 2 cells. Answer: False (More cells = More current = Stronger magnet = More clips).

3. Multiple Choice Analysis

Scenario: Current flows through Nichrome wire.

• (i) Wire becomes warm $\rightarrow$ True (Heating Effect).
• (ii) Compass deflects $\rightarrow$ True (Magnetic Effect). Answer: (c) Both (i) and (ii) are correct.

4. Match the columns

5. Why is Nichrome used in heating devices?

Answer: (i) It offers high resistance (generating more heat). (ii) It does not melt easily at high temperatures (high melting point). (iii) It does not oxidize (burn) easily when red hot. From the options provided in the book, the best fit is related to its ability to generate heat due to resistance.

6. Convenience of Electric Heating vs Firewood

Answer: Electric heating is more convenient because:

1. Pollution: It does not produce smoke or harmful gases (indoor air quality).
2. Control: Temperature can be easily regulated (switching on/off instantly).
3. Efficiency: Less energy wastage compared to open fires.
4. Societal Impact: Reduces deforestation and respiratory diseases caused by smoke inhalation.

7. Compass Deflection Analysis

(i) Direction of Current: Current flows from Positive (+) to Negative (-). In diagram 4.4a, trace the wire from the cell’s positive terminal. (ii) Why it moves: The current-carrying wire creates a magnetic field that interacts with the magnetic field of the compass needle, causing a force that deflects it. (iii) Reversing Terminals: The direction of the magnetic field will reverse, so the compass needle will deflect in the opposite direction.

8. Sumana’s Electromagnet Problem

Scenario: Switch is OFF, clips fall, but wire is still warm. Wait, the question says she FORGETS to move switch to OFF. Correct Reading: “Sumana forgets to move the switch… to OFF position… After some time, the iron nail no longer picks up clips, but wire is warm.” Answer:

1. Why it stopped lifting: The battery has likely drained out (died) because it was left ON for too long. The current dropped so low that the magnetic field became too weak to hold the clips.
2. Why still warm: Even a weak residual current can generate some heat, or the heat generated earlier has not yet dissipated completely.

9. Lemon Battery Circuit (Fig 4.11)

Answer: Circuit (b) will glow.

• Reason: For a battery to work, you need two different metals as electrodes.
  • (a) uses Iron nail and Iron nail. No potential difference.
  • (b) uses Iron nail and Copper strip. This creates a potential difference.

10. Neha’s Coil (Removing the Nail)

Answer:

• Will it deflect? Yes. A current-carrying coil (solenoid) produces a magnetic field even without a core.
• More or Less? The deflection will be less. The iron nail (ferromagnetic core) significantly strengthens the magnetic field. Removing it weakens the magnet.

11. Coils of different metals (Iron, Copper, Aluminium, Nichrome)

Question: Which circuits cause compass deflection? Answer: (iv) In all four circuits.

• Reason: Oersted’s discovery applies to any conductor carrying current. As long as current flows through Iron, Copper, Aluminium, or Nichrome, a magnetic field is generated around the wire.