Electricity: Magnetic and Heating Effects
Keep the curiosity alive
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.
2. Choose the correct option:
(i) Dry cells are less portable compared to Voltaic cells.(True/False)
Answer: False
(ii) A coil becomes an electromagnet only when electric current flows through it. (True/False)
Answer: True
(iii) An electromagnet, using a single cell, attracts more iron paper clips than the same electromagnet with a battery of 2 cells. (True/False)
Answer: False
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
Answer:- (c) Both (i) and (ii) are correct
4. Match the items in Column A with those in Column B.
Answer:-
| Column A | Column B |
|---|---|
| (i) Voltaic cell | (d) Generates electricity by chemical reactions |
| (ii) Electric iron | (c) Works on heating effect of electric current |
| (iii) Nichrome wire | (a) Best suited for electric heater |
| (iv) Electromagnet | (b) Works on magnetic effect of electric current |
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.
Answer:- (ii) generates more heat for a given current
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.
Answer:- Electric heating devices are more convenient and safer for society because:
1. They do not produce smoke, so they help keep the air clean and reduce indoor air pollution.
2.They are easier to use-just switch them on and off; no need to gather or burn wood or charcoal.
3.They save time and effort, especially for women and children in rural areas who often collect firewood.
4.They reduce deforestation, as less wood is needed for burning.
5.They are safer, as there is a lower risk of fire accidents or breathing problems.
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.
Answer:-
(ii) Explain why the compass needle moves when current flows.
Answer:- The compass needle moves when current flows because the electric current through the wire produces a magnetic field around it. This magnetic field interacts with the magnetic field of the compass needle, causing it to deflect from its original north-south direction.
(iii) Predict what would happen to the deflection if you reverse the battery terminals.
Answer:- If you reverse the battery terminals, the direction of the electric current will reverse, flowing from end B to end A. This will cause the magnetic field to reverse, and the compass needle will deflect in the opposite direction compared to its original deflection.
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
Answer:- The lifting electromagnet stopped lifting the iron paper clips because Sumana forgot to move the switch to the OFF position, which likely caused the battery to drain or the cell to become “dead.” When a cell is used for a long time without a break, the chemicals inside it get used up, and it can no longer supply enough electric current to produce a strong magnetic field. This weak magnetic field is not strong enough to attract the iron paper clips. The wire wrapped around the iron nail is still warm because, even with a weak current, the resistance in the wire converts some electrical energy into heat energy, known as the heating effect of electric current.
9. In Fig. 4.11, in which case the LED will glow when the switch is closed?
Answer:- In Fig. 4.11, the LED will glow when the switch is closed in case (a), where the electrodes are placed in lemon juice. This is because lemon juice acts as an electrolyte, enabling a chemical reaction between the copper strip and iron nail to generate electric current, which can power the LED. In case(b), with pure water, the LED will not glow as pure water does not conduct electricity effectively due to the absence of ions.
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?
Answer:- Yes, the coil will still deflect the compass even after Neha removes the iron nail. This is because a current-carrying coil of wire produces a magnetic field, and the compass needle responds to that magnetic field.
However, the deflection will be less than before. This is because when the iron nail is present inside the coil, it acts as a core and makes the electromagnet stronger. Without the iron nail, the magnetic effect is weaker, so the compass needle shows less deflection.
11. We have four coils, of similar shape and size, made up from iron, copper, aluminium, and nichrome as shown in Fig. 4.12.
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
Answer:- (iv) In all four circuits
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