NCERT 7th Class (CBSE) Science: Electric Current and its effects

Question: Rita used a fuse wire with a 100 amperes specification in a circuit at home which draws a maximum current of 20 amperes when all devices in the circuit are switched on. Do you think she used the correct fuse wire? What will you advise her to do?

Answer: She did not use correct wire because it is not necessary far a 20 amperes wire to used 100 amperes fuse wire. She is wasting a lot of energy. I will advise her to use 21 or more than that amperes wire.

Question: A coil with no current passing through it is suspended freely. It points in the east-west direction. Explain what will happen if a current is passed through the coil.

Answer: It a current is passed through the coil it will become a magnet and the coil will face north-south direction.

Question: You have seen that the heating effect of current can be put to good use. Can you think of situations where this effect result in wastage of energy.

Answer: Situations such as an electric bulb, tube light, refrigerator, television etc. encourage the wastage of energy as no heat is required in this.

Question: Name any two effects of electric current.

Answer: Two effects of electric current:
(i) Heating effect
(ii) Magnetic effect

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

Answer: The current flowing through the wire produces magnetic effect around it which deflect the needle of the compass kept nearby as it is also a piece of magnet.

Question: Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.

Answer: No, an electromagnet can be used for separating plastic bags from a garbage heap. Since plastic bags are non-magnetic material and electromagnet is used to seperate only the magnetic materials.

Question: An 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.

Answer: No, I will not agree with the electrician. The wire use for making fuse have low melting point and therefore any wire cannot be used to replace the fuse. In most cases, the ordinary wires have high melting point.

Question: Zubeda made an electric circuit using a cell holder, a switch and a bulb. When she put the switch in the ON position, the bulb did not glow. Help Zubeda in identifying the possible defects in the circuit.

Answer: Possible defect:
(i) Bulb may have fused.
(ii) Rubber band of cell holder may not be tight and connections are loose.
(ii) Terminals of the cells may not be in the correct positions.