Topic outline

• Electric Current and its Effects

Q31. An electric bulb results in wastage of electricity. Comment

Ans. An electric bulb is used for light but it also gives heat. This is not desirable. This results in the wastage of electricity. This wastage can be reduced by using fluorescent tube lights in place of the bulbs. Compact fluorescent lamps (CFLs) also reduce wastage and can be fixed in the ordinary bulb holders.

Q32. What is the use of electrical fuse?

Ans. In all buildings fuses are inserted in all electrical circuits. There is a maximum limit on the current which can safely flow through a circuit. If by accident the current exceeds this safe limit, the wires may become overheated and may cause fire. If a proper fuse is there in the circuit, it will blow off and break the circuit. A fuse is thus a safety device which prevents damages to electrical circuits and possible fires.

Q33. What are the uses of electromagnets?

Ans. The electromagnets can be made very strong and can lift very heavy loads. The end of such a crane has a strong electromagnet attached to it. The electromagnets are also used to separate magnetic material from the junk. Doctors use tiny electromagnets to take out small pieces of magnetic material that have accidentally fallen in the eye. Many toys also have electromagnets inside them. Electromagnets are also used in electric bells.

Q34. When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position. Explain.

Ans. We know that the needle of a compass is a tiny magnet, which points in north-south direction. When we bring a magnet close to it, the needle gets deflected. We have also seen that compass needle gets deflected when the current flows in a nearby wire. This is so because when electric current passes through a wire, it behaves like a magnet. This is the magnetic effect of the electric current.

Q35. Write the key points about electric circuit.

Ans. Key Points

i.        Notice that the key or switch can be placed anywhere in the circuit.

ii.        When the switch is in the ‘ON’ position, the circuit from the positive terminal of the battery to the negative terminal is complete. The circuit is then said to be closed and the current flows throughout the circuit instantly.

iii.        When the switch is in the ‘OFF’ position, the circuit is incomplete. It is said to be open. No current flows through any part of the circuit.

Q36. Will the compass needle show deflection when the switch in the circuit shown below is closed?

Image from NCERT

Ans. No, the compass needle will not show deflection when the switch in the circuit shown above is closed because compass needle shows deflection only when current passes through the wire.

Q37. Draw in your notebook the symbols to represent the following components of electrical circuits: connecting wires, switch in the ‘OFF’ position, bulb, cell, switch in the ‘ON’ position, and battery.

Ans.

 Electric Components Symbol Connecting wires Switch in the ‘OFF’ position Bulb Cell Switch in the ‘ON’ position Battery

Q38. In the circuit shown in the below Fig.

Image from NCERT

(i) Would any of the bulbs glow when the switch is in the ‘OFF’ position?(ii) What will be the order in which the bulbs A, B and C will glow when the switch is moved to the ‘ON’ position?

Ans. i. No, bulb will not glow when the switch is in the ‘OFF’ position because current does not flow through the circuit.

ii. All the bulbs will glow simultaneously when the switch is moved to the ‘ON’ position.