Here are the questions and their corresponding answers based entirely on the textbook chapter you provided.
Let Us Enhance Our Learning (End of Chapter Exercises)
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.
- Answer: Statement (i) is incorrect. An electric cell or battery is the source of electrical energy in a circuit. A switch is a device that completes or breaks the circuit.
2. Observe Fig. 3.16. With which material connected between the ends A and B, the lamp will not glow?
- Answer: The lamp will not glow if an insulator (a poor conductor of electricity) is connected between ends A and B. Examples of insulators mentioned in the text include wood, plastic, glass, paper, wax, rubber, and ceramics. The lamp will only glow if a conductor, such as a metal wire, key, or coin, completes the circuit.
3. In Fig. 3.17, if the filament of one of the lamps is broken, will the other glow? Justify your answer.
- Answer: No, the other lamp will not glow. A broken filament stops the flow of electric current, creating a broken or open path in the circuit. Because the current cannot pass through the first broken lamp to reach the second one, neither lamp will glow.
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?
- Answer: No, the lamp will not glow. The covering on electric wires is made of insulators like plastic or rubber, which do not allow electric current to pass through. To complete the circuit, the plastic covering must be removed to expose the metal conductor inside.
5. Draw a circuit diagram for a simple torch using symbols for electric components.
- Answer: A proper circuit diagram for a torch would include the symbol for a battery (two or more cells connected), a switch, and a lamp. These components must be connected in a continuous loop using straight lines to represent wires. (Note: You can reference Table 3.2 in your book for the exact symbols to draw )
6. In Fig. 3.18:
- (i) If S2 is in ‘ON’ position, S1 is in ‘OFF’ position, which lamp(s) will glow? None of the lamps will glow. S1 is located on the main path connected to the battery; if it is ‘OFF’, the entire circuit is broken.
- (ii) If S2 is in ‘OFF’ position, S1 is in ‘ON’ position, which lamp(s) will glow? Only L1 will glow. S1 completes the circuit for L1, but the open S2 switch breaks the path for L2.
- (iii) If S1 and S2 both are in ‘ON’ position, which lamp(s) will glow? Both L1 and L2 will glow because the path is completely closed for both.
- (iv) If both S1 and S2 are in ‘OFF’ position, which lamp(s) will glow? Neither lamp will glow because the circuit is completely open.
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?
- Answer: Possible reasons include:
- The electric cell is used up (dead).
- The lamp is “fused” because its filament is broken.
- The connections between the wires, cell, and lamp are loose or not touching properly.
- If an LED was used instead of an incandescent lamp, its positive and negative terminals might be connected in the wrong direction.
8. In Fig. 3.20, in which case(s) the lamp/LED will not glow when the switch is closed?
- Answer: The lamp will not glow in case (c). Case (c) shows an LED, which only allows current to pass in one direction. An LED only lights up when its positive terminal is connected to the positive terminal of the battery, and its negative terminal is connected to the negative terminal of the battery. In diagram (c), it is connected backward.
9. Suppose the ‘+’ and ‘-‘ symbols cannot be read on a battery. Suggest a method to identify the two terminals of this battery.
- Answer: You can use an LED to identify the terminals. Connect the LED to the battery using wires. Because an LED only glows when its positive terminal (longer wire) is connected to the positive terminal of the battery and its negative terminal (shorter wire) is connected to the battery’s negative terminal , you will know you have found the positive battery terminal when the LED successfully glows.
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.
- Answer:
- (i) Items required: A lamp (or LED), a cell holder, and connecting wires with exposed metal ends.
- (ii) Procedure: Create a simple tester circuit by attaching wires to the lamp holder. Insert cell A into the cell holder and connect the wires to the lamp to complete the circuit. Observe if the lamp glows. Disconnect, remove cell A, and repeat this exact process for cells B, C, D, E, and F.
- (iii) Conclusion: If the lamp glows, the cell is working and providing electric current. If the lamp does not glow, the cell is not working.
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.
- Answer: Assuming the image shows an incorrect battery configuration, the cells must be arranged so that the positive terminal of one cell connects to the negative terminal of the next cell. If they are arranged side-by-side, a wire or metal strip must cross over to connect the positive terminal to the negative terminal correctly.
Activity Tables Found in the Chapter
Table 3.1: Trying to make the lamp glow
- Arrangement 1: Wires properly connect both cell terminals to both lamp terminals. Observation: The lamp glows.
- Arrangements 2, 3, 4, & 5: The circuit is incomplete (either wires are broken, or both wires are touching only one terminal). Observation: The lamp does not glow.
- Arrangement 6: Wires properly connect both terminals (reversed from 1). Observation: The lamp glows because for an incandescent lamp, terminal direction does not matter.
Table 3.3: Identifying Conductors and Insulators
- 1. Stick (Wood): Lamp does not glow $\rightarrow$ Insulator
- 2. Scale (Plastic): Lamp does not glow $\rightarrow$ Insulator
- 3. Bangle (Glass): Lamp does not glow $\rightarrow$ Insulator
- 4. Paper strip (Paper): Lamp does not glow $\rightarrow$ Insulator
- 5. Candle (Wax): Lamp does not glow $\rightarrow$ Insulator
- 6. Key (Metal): Lamp glows $\rightarrow$ Conductor
- 7. Eraser (Rubber): Lamp does not glow $\rightarrow$ Insulator