Class 7 Science
NCERT Solution Part 2
Question 8: Fill in the blanks:
- Longer line in the symbol for a cell represents its …………..terminal.
- The combination of two or more cells is called a ……………
- When current is switched ‘on’ in a room heater, it ……………….
- The safety device based on the heating effect of electric current is called a ……………
Answer: (a) Positive, (b) Battery, (c) heats up, (d) electric fuse
Question 9: Mark ‘T’ if the statement is true and ‘F’ if it is false:
- To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell.
- When the electric current through the fuse exceeds a certain limit, the fuse wire melts and breaks.
- An electromagnet does not attract a piece of iron.
- An electric bell has an electromagnet.
Answer: (a) F, (b) T, (c) F, (d) T
Question 10: Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.
Answer: Since plastic is a non-magnetic material, so electromagnet cannot be used to separate plastic bags from a garbage heap.
Question 11: 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: A special wire with low melting point should be used for the fuse wire and any other wire would not serve the purpose. Hence, I would not agree with the electrician.
Question 12: Zubeda made an electric circuit using a cell holder shown in the given figure (textbook), 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: There can be following possibilities:
- The terminals of cells are not in correct position.
- The connections are loose.
- The bulb may have fused.
Question 13: In the circuit shown in the figure
(a) Would any of the bulb glow when the switch is in the ‘OFF’ position?
Answer: None of the bulbs would glow.
(b) What will be the order in which the bulbs A, B and C will glow when the switch is moved to the ‘ON’ position?
Answer: All the bulbs would glow at once.