Questions are taken verbatim from the NCERT textbook; answers were grounded against the chapter's content during generation. Items needing review are marked.
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1Exercises7 questions
Q.5Name any two effects of electric current.v
Answer:Two effects of electric current are the heating effect and the magnetic effect.
Q.6When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position. Explain.v
Answer:A current-carrying wire behaves like a magnet and produces a magnetic field around it. This magnetic field affects the compass needle, so the needle is deflected from its north-south position.
Q.8Fill in the blanks:
(a) Longer line in the symbol for a cell represents its __________ terminal.
(b) The combination of two or more cells is called a __________.
(c) When current is switched 'on' in a room heater, it __________.
(d) The safety device based on the heating effect of electric current is called a __________.v
Answer:(a) positive
(b) battery
(c) becomes hot
(d) fuse
Q.9Mark 'T' if the statement is true and 'F' if it is false:
(a) To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell. (T/F)
(b) When the electric current through the fuse exceeds a certain limit, the fuse wire melts and breaks. (T/F)
(c) An electromagnet does not attract a piece of iron. (T/F)
(d) An electric bell has an electromagnet. (T/F)v
SolutionCells in a battery are connected positive to negative. Excess current heats and melts the fuse wire. An electromagnet attracts iron, and an electric bell uses an electromagnet.
Answer:(a) F
(b) T
(c) F
(d) T
Q.10Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.v
Answer:No. An electromagnet attracts magnetic materials such as iron, but plastic is non-magnetic. Therefore it cannot be used to separate plastic bags from garbage.
Q.11An electrician is carrying out some repairs in your house. He wants to replace a fuse by a piece of wire. Would you agree? Give reasons for your response.v
Answer:No. A fuse is a safety device made of wire that melts when current exceeds a safe limit, breaking the circuit. An ordinary wire may not melt at the right current and can cause overheating, damage or fire.
Q.14An electric iron of 1 kW is operated at 220 V. Which of the following fuses should be used in the circuit?
(i) 1 A (ii) 3 A (iii) 5 A (iv) 13 Av
- a. 1 A
- b. 3 A
- c. 5 A
- d. all of these
SolutionCurrent = power / voltage = 1000 W / 220 V ≈ 4.55 A. The fuse should be just above the working current, so 5 A is suitable.