Electricity: Magnetic and Heating Effects — Hard

Q1. An electric current flows through a nichrome wire for a short time. Consider the statements: (i) The wire becomes warm. (ii) A magnetic compass placed below the wire is deflected. Choose the correct option

• A. Only (i) is correct
• B. Only (ii) is correct
• C. Both (i) and (ii) are correct
• D. Both (i) and (ii) are not correct

Q2. Neha sets up the same coil as in Activity 4.4 but slides the iron nail out, leaving only the coiled wire. With the same current, what happens to the magnetic compass placed near the coil?

• A. The compass needle still deflects, but the deflection is less than before
• B. The compass needle does not deflect at all
• C. The deflection becomes much more than before
• D. The needle rotates a full circle

Q3. Four coils of identical shape and size are made from iron, copper, aluminium and nichrome (Fig. 4.13). Each is connected to the same cell and switch. When current is passed, magnetic compass needles placed near the coils will show deflection in

• A. Only circuit (a) — the iron coil
• B. All four circuits
• C. Only circuits (a) and (b)
• D. Only circuits (a), (b) and (c)

Q4. Sumana forgets to switch OFF her lifting electromagnet. After some time, the iron nail no longer picks up paper clips, but the wire around the nail is still warm. The MOST LIKELY reason is

• A. The clips have become permanent magnets and repel the nail
• B. The wire has changed into nichrome with time
• C. The nail has melted inside the coil
• D. The cell has weakened — current is too small for the magnetic effect, but enough current still flows to warm the wire

Q5. Two cells are set up: (a) an iron nail and copper strip dipped in lemon juice with a connected LED; (b) the same arrangement but in pure water. When the switch is closed, the LED glows in

• A. Only case (a)
• B. Only case (b)
• C. Both (a) and (b)
• D. Neither (a) nor (b)

Q6. Match Column A with Column B: (i) Voltaic cell (ii) Electric iron (iii) Nichrome wire (iv) Electromagnet — with (a) Best suited for electric heater (b) Works on magnetic effect (c) Works on heating effect (d) Generates electricity by chemical reactions. The correct match is

• A. (i)-(c), (ii)-(a), (iii)-(b), (iv)-(d)
• B. (i)-(d), (ii)-(c), (iii)-(a), (iv)-(b)
• C. (i)-(b), (ii)-(d), (iii)-(c), (iv)-(a)
• D. (i)-(a), (ii)-(b), (iii)-(d), (iv)-(c)

Q7. Consider three statements about the heat generated in a current-carrying wire: (I) It depends on the material of the wire. (II) It depends on the thickness and length of the wire. (III) It depends on the time for which current flows. Which are correct?

• A. I and II only
• B. II and III only
• C. I and III only
• D. All three

Q8. Assertion (A): An incandescent torch lamp sometimes gets warm during a circuit activity. Reason (R): Its filament is heated by the electric current flowing through it. Choose the correct option

• A. Both A and R are true, and R is the correct explanation of A
• B. Both A and R are true, but R is NOT the correct explanation of A
• C. A is true, R is false
• D. A is false, R is true

Q9. Look at Fig. 4.4a where a compass placed near an electromagnet shows a deflection. If you reverse the terminals of the battery, what will happen to the deflection?

• A. The deflection will be in the opposite direction (poles of the electromagnet reverse)
• B. There will be no deflection at all
• C. The deflection will become exactly twice as large
• D. The compass needle will start spinning continuously

Q10. Activity 4.5 is repeated for the same duration, once with one cell and once with a battery of two cells. The heat generated in the nichrome wire is more in the two-cell experiment. The BEST reason is

• A. Two cells together act as a magnet and supply heat directly
• B. Two cells double the resistance of the wire
• C. Two cells cool the wire less than one cell does
• D. The amount of heat generated depends on the magnitude of current, and two cells give a larger current

Q11. Nichrome wire is commonly used in electrical heating devices because it: (I) is a good conductor of electricity (II) generates more heat for a given current (III) is cheaper than copper (IV) is an insulator of electricity. Which combination is correct?

• A. I and II only
• B. I, II and III only
• C. II and IV only
• D. All four

Q12. A factory needs to lift, move and sort heavy iron pieces from a pile of waste, then drop them in a separate bin. Which of these would BEST suit this task?

• A. A bar magnet tied to a rope
• B. A lifting electromagnet whose current can be switched ON and OFF
• C. An incandescent torch lamp
• D. A nichrome heating coil

Q13. Three statements about a dry cell: (I) The electrolyte is a thick moist paste, not a liquid. (II) The zinc container acts as the positive terminal. (III) The central carbon rod is surrounded by the paste-like electrolyte. Which are correct?

• A. I and III only
• B. II and III only
• C. I and II only
• D. All three

Q14. In the lemon-cell activity, students connect an LED across a chain of lemons but the LED does not glow. They then reverse the LED's terminals and it glows. The reason is

• A. Lemon juice flows in only one direction
• B. Current can pass through an LED only when its positive (longer wire) is connected to the positive of the battery
• C. The LED was broken in the first try
• D. Iron nails work as electrodes only when warm

Q15. Assertion (A): A 'dead' battery should not be thrown into regular household garbage. Reason (R): Even when a battery stops working, it may still contain acids and metals like lead, cadmium, nickel or lithium that can harm the environment. Choose the correct option

• A. Both A and R are true, and R is the correct explanation of A
• B. Both A and R are true, but R is NOT the correct explanation of A
• C. A is true, R is false
• D. A is false, R is true