Chapter 3 Solutions — Electricity: Circuits and Their Components

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1. 1.
   Choose the incorrect statement.

   • (i) A switch is the source of electric current in a circuit.
   • (ii) A switch helps to complete or break the circuit.
   • (iii) A switch helps us to use electricity as per our requirement.
   • (iv) When the switch is in 'OFF' position, there is an air gap between its terminals.
2. 2.
   Observe Fig. 3.16. With which material connected between the ends A and B, the lamp will not glow? [Fig. 3.16 shows a conduction-tester circuit with a cell and lamp, and two free wire ends A and B where different materials can be inserted.]
3. 3.
   In Fig. 3.17, if the filament of one of the lamps is broken, will the other glow? Justify your answer. [Fig. 3.17 shows two lamps connected in series with an electric cell.]
4. 4.
   A student forgot to remove the insulator covering from the connecting wires while making a circuit. If the lamp and the cell are working properly, will the lamp glow?
5. 5.
   Draw a circuit diagram for a simple torch using symbols for electric components.
6. 6.
   In Fig. 3.18:

   • (i) If S2 is in 'ON' position, S1 is in 'OFF' position, which lamp(s) will glow?
   • (ii) If S2 is in 'OFF' position, S1 is in 'ON' position, which lamp(s) will glow?
   • (iii) If S1 and S2 both are in 'ON' position, which lamp(s) will glow?
   • (iv) If both S1 and S2 are in 'OFF' position, which lamp(s) will glow? [Fig. 3.18 shows a circuit with lamps L1 and L2, and switches S1 and S2. S1 is…
7. 7.
   Vidyut has made the circuit as shown in Fig. 3.19. Even after closing the circuit, the lamp does not glow. What can be the possible reasons? List as many possible reasons as you can for this faulty operation. What will you do to find out why the lamp did not glow? [Fig. 3.19 shows a simple closed circuit with a cell, switch (closed), lamp, and wires.]
8. 8.
   In Fig. 3.20, in which case(s) the lamp/LED will not glow when the switch is closed? [Fig. 3.20 shows four series circuits, each with a switch:

   • (a) an incandescent lamp with a single cell;
   • (b) an incandescent lamp with a single cell;
   • (c) an LED with a battery;
   • (d) an LED with a battery. The LED points the same way in
   • (c) and (d), but the battery is connected the opposite way round in the two…
9. 9.
   Suppose the '+' and '–' symbols cannot be read on a battery. Suggest a method to identify the two terminals of this battery.
10. 10.
    You are given six cells marked A, B, C, D, E, and F. Some of these are working and some are not. Design an activity to identify which of them are working.

    • (i) List the items that you require.
    • (ii) Write the procedure that you will follow.
    • (iii) With the items, carry out the activity to identify the cells that are working.
11. 11.
    Using an LED that requires two cells in series to glow, Tanya made the circuit as shown in Fig. 3.21. Will the lamp glow? If not, draw the wires for correct connections. [Fig. 3.21 shows two cells stacked one above the other, each with '−' on the left and '+' on the right. A black wire joins the two LEFT (negative) ends of the cells together, while the two RIGHT (positive) ends are led out by…