Chapter 4 Solutions — Electricity: Magnetic and Heating Effects

Keep the Curiosity Alive

1. 1.
   Fill in the blanks:

   • (i) The solution used in a Voltaic cell is called ________.
   • (ii) A current carrying coil behaves like a _______ .
2. 2.
   Choose the correct option:

   • (i) Dry cells are less portable compared to Voltaic cells. (True/False)
   • (ii) A coil becomes an electromagnet only when electric current flows through it. (True/False)
   • (iii) An electromagnet, using a single cell, attracts more iron paper clips than the same electromagnet with a battery of 2 cells. (True/False)
3. 3.
   An electric current flows through a nichrome wire for a short time.

   • (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
4. 4.
   Match the items in Column A with those in Column B. Column A:

   • (i) Voltaic cell
   • (ii) Electric iron
   • (iii) Nichrome wire
   • (iv) Electromagnet Column B:
   • (a) Best suited for electric heater
   • (b) Works on magnetic effect of electric current
   • (c) Works on heating effect of electric current
   • (d) Generates electricity by chemical reactions
5. 5.
   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.
6. 6.
   Electric heating devices (like an electric heater or a stove) are often considered more convenient than traditional heating methods (like burning firewood or charcoal). Give reason(s) to support this statement considering societal impact.
7. 7.
   Look at the Fig. 4.4a. If the compass placed near the coil deflects:

   • (i) Draw an arrow on the diagram to show the path of the electric current.
   • (ii) Explain why the compass needle moves when current flows.
   • (iii) Predict what would happen to the deflection if you reverse the battery terminals.
8. 8.
   Suppose Sumana forgets to move the switch of her lifting electromagnet model to OFF position (in introduction story). After some time, the iron nail no longer picks up the iron paper clips, but the wire wrapped around the iron nail is still warm. Why did the lifting electromagnet stop lifting the clips? Give possible reasons.
9. 9.
   In Fig. 4.12, in which case the LED will glow when the switch is closed?

   • (a) Iron nail + Copper strip + Lemon juice
   • (b) Iron nail + Copper strip + Pure water
10. 10.
    Neha keeps the coil exactly the same as in Activity 4.4 but slides the iron nail out, leaving only the coiled wire. Will the coil still deflect the compass? If yes, will the deflection be more or less than before?
11. 11.
    We have four coils, of similar shape and size, made up from iron, copper, aluminium, and nichrome as shown in Fig. 4.13. When current is passed through the coils, compass needles placed near the coils will show deflection.

    • (i) Only in circuit
    • (a) (ii) Only in circuits
    • (a) and
    • (b) (iii) Only in circuits (a), (b), and
    • (c) (iv) In all four circuits