Electricity: Circuits and their Components - Class 7 NCERT Solutions

In this article, answers and detailed solutions of the NCERT questions of chapter 3 "Electricity: Circuits and their Components" are provided. 

Electricity: Circuits and their Components - Class 7 New NCERT Solutions

Q1. 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.

Ans. a) A switch a source of light? Justify.

Ans: No. A switch is not a source of light; its function is to control the flow of current by completing or breaking the circuit.

Q2. Observe Fig. 3.16. With which material connected between the ends A and B, the lamp will not glow?

Ans. 
The lamp will not glow if insulator is used to connect the wires. Insulators do not allow electric current to flow through them, creating a break in the electrical path. Examples of insulators include Wood, Plastic, Rubber, Glass etc. 

Q3. In Fig. 3.17, if the fi lament of one of the lamps is broken, will the other glow? Justify your answer. 

Ans. If the filament is broken, it will create a gap in the circuit. This results in an open circuit, which stops the flow of current to all components. So, none of the lamp will glow even if filament of one lamp is broken. 

Q4. 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?

Ans. The covering of an electric wire is made with rubber which is an insulator. If it is not removed, it will block the flow electricity. Only the metal part of the wire can conduct electricity to complete the circuit. So, if the covering from the connecting wires is not removed then the lamp will not glow. 

Q5. Draw a circuit diagram for a simple torch using symbols for electric components.

Ans. The labelled diagram for a simple LED torch is drawn below: 

Q6. 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?

Ans. 

The lamps will glow only when both S1 and S2 are on. Even if one of the switches is off, it will stop the complete flow of current and none of the lamp will glow.

(i) None of the lamp glow

(ii) None of the lamp glow

(iii) Both lamps will glow. 

(iv) None of the lamp glow

Q7. 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?

Ans. If the lamp doesn't glow even after closing the circuit, then below reasons might be true: 

1. Lamp might be fused or the filament might be broken. For fixing this, we can try changing the Lamp.
2. Cell might be discharged. To fix this issue with the cell, we can replace or recharge it. 
3. Cell must be inserted inside the holder inverted. We can revert the sides of cell to make contact of the terminals correctly. 
4. There might be an internal breakage in wires. To fix this, we can try reconnecting or replacing the wires. 

Q8. In Fig. 3.20, in which case(s) the lamp will not glow when theswitch is closed?

Ans. The lamp does not glow in Case (c) because the LED is connected in the wrong direction. An LED allows current to flow only in one direction. Here, the battery terminals and LED terminals do not match, so current cannot pass through the circuit. For making the LED glow, positive wire of LED must be connected to the positive terminal of the battery. And negative wire must be connected with the negative terminal of the battery. 

In Cases (a) and (b), normal bulbs glow because they work in both directions. Bulbs do not have any positive or negative terminals. In Case (d), the LED is connected correctly, so the lamp glows.

Q9. Suppose the ‘+’ and ‘–’ symbols cannot be read on a battery. Suggest a method to identify the two terminals of this battery.

Ans. The positive and negative ends of the battery can be identified by using an LED. The long wire of LED shows positive terminal and short wire shows negative terminal. If LED connected to the battery glows, then long wire must be connected to the positive terminal of the battery and short wire must be connected to the negative terminal of the battery. 

Q10. 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.

Ans. 

(i) Items Required

• A small bulb or LED
• Two connecting wires
• Cell holder (optional)
• Six cells marked A, B, C, D, E, and F

(ii) Procedure

1. Connect the bulb and wires to make a simple circuit.
2. Place one cell in the circuit.
3. Observe whether the bulb glows or not.
4. Repeat the same process for all six cells one by one.
5. Note down the cells that make the bulb glow.

Observation and Conclusion

• If the bulb glows, the cell is working.
• If the bulb does not glow, the cell is not working.
• In this way, we can identify the working and non-working cells.

Q11. An LED 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. 

Ans. 

Also see : Class 7 Science All Chapter's NCERT Solutions