Question 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.

Accepted Answer

The incorrect statement is (i) A switch is the source of electric current in a circuit.
Explanation: The source of electric current is an electric cell or battery, not the switch. The switch only helps to complete or break the circuit to control the flow of current. — Step-by-step:
- Identify the role of a switch: It completes or breaks the circuit.
- Identify the source of current: It is the electric cell or battery.
- Therefore, statement (i) is incorrect.

Question 2

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

Accepted Answer

The lamp will not glow if an insulator is connected between ends A and B.
Explanation: An insulator does not allow electric current to pass through it, so the circuit will remain incomplete and the lamp will not glow. — Step-by-step:
- Identify materials as conductors or insulators.
- Connect a conductor: current flows, lamp glows.
- Connect an insulator: current does not flow, lamp does not glow.

Question 3

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

Accepted Answer

No, the other lamp will not glow.
Explanation: In the given figure, the lamps are connected in series. If the filament of one lamp is broken, the circuit becomes open and current cannot flow through the circuit. Hence, the other lamp will not glow. — Step-by-step:
- Identify the type of connection (series).
- Broken filament means open circuit.
- No current flows, so no lamp glows.

Question 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?

Accepted Answer

No, the lamp will not glow.
Explanation: The insulator covering on the wires prevents the flow of electric current. Since the wires are insulated, the circuit will not be complete and current will not flow to the lamp. — Step-by-step:
- Insulator covering prevents current flow.
- Circuit remains incomplete.
- Lamp does not receive current, so it does not glow.

Question 5

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

Accepted Answer

A simple torch circuit diagram includes:
- A battery as the source of electrical energy.
- A switch to control the circuit.
- A lamp (bulb) as the load.
The circuit diagram shows the battery connected in series with the switch and the lamp. When the switch is closed, current flows from the positive terminal of the battery through the lamp and back to the negative terminal, lighting the lamp. — Step-by-step:
- Identify components: battery, switch, lamp.
- Connect them in series.
- Use standard circuit symbols: battery (long and short lines), switch (open/closed), lamp (circle with filament).
- Draw the circuit diagram accordingly.

Question 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?

Accepted Answer

(i) If S2 is ON and S1 is OFF, only lamp L2 will glow.
(ii) If S2 is OFF and S1 is ON, only lamp L1 will glow.
(iii) If both S1 and S2 are ON, both lamps L1 and L2 will glow.
(iv) If both S1 and S2 are OFF, no lamp will glow.

Explanation: Each switch controls the current to its respective lamp. When a switch is ON, it completes the circuit for that lamp allowing current to flow and the lamp to glow. When OFF, the circuit is broken and the lamp does not glow. — Step-by-step:
- Analyze the circuit connections.
- Identify which switch controls which lamp.
- Determine the state of each lamp based on switch positions.
- Summarize the glow status for each case.

Question 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?

Accepted Answer

Possible reasons why the lamp does not glow:
- The cell may be dead or not providing current.
- The lamp may be faulty or its filament may be broken.
- The switch may not be properly closed.
- There may be a loose connection or broken wire in the circuit.
- The wires may have insulation not removed, preventing current flow.

To find out why the lamp did not glow:
- Check if the cell is working by testing it with a voltmeter or another lamp.
- Check the lamp by replacing it with a known working lamp.
- Ensure the switch is properly closed.
- Inspect all connections and wires for continuity.
- Remove insulation from wires if present.

Explanation: By systematically checking each component and connection, the faulty part can be identified and corrected. — Step-by-step:
- List all components and their possible faults.
- Test each component individually.
- Check connections and switch operation.
- Identify and fix the faulty part.

Question 8

In Fig. 3.20, in which case(s) the lamp/LED will not glow when the switch is closed?
(a)
(b)
(c)
(d)

Accepted Answer

The lamp/LED will not glow in cases (b) and (c).
Explanation:
- In (b), the LED is connected in reverse polarity; LEDs allow current in one direction only.
- In (c), the circuit is incomplete or open, so current cannot flow.
- In (a) and (d), the LED/lamp is connected correctly and the circuit is complete, so it glows. — Step-by-step:
- Check the direction of LED in each case.
- Identify if the circuit is complete.
- LEDs glow only when connected in correct polarity and circuit is closed.

Question 9

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

Accepted Answer

Method to identify terminals:
- Use a multimeter to check the polarity; the red probe connects to positive and black to negative.
- Alternatively, connect the battery to a known LED or lamp circuit; if the LED does not glow, reverse the connections.
- The terminal connected to the longer wire of an LED is positive.

Explanation: The positive terminal is usually at higher potential and can be identified by polarity testing or by observing the LED glow direction. — Step-by-step:
- Use a multimeter to measure voltage and polarity.
- Connect battery to LED and check if it glows.
- Reverse connections if LED does not glow.
- Identify positive and negative terminals accordingly.

Question 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.

Accepted Answer

(i) Items required:
- Lamp or LED
- Connecting wires
- Switch
- Battery holder or clips

(ii) Procedure:
- Connect each cell individually in a simple circuit with the lamp or LED and switch.
- Close the switch and observe if the lamp/LED glows.
- If it glows, the cell is working; if not, the cell is faulty.

(iii) Carry out the activity by testing each cell one by one using the above procedure and note down which cells are working and which are not. — Step-by-step:
- Prepare a simple circuit.
- Test each cell individually.
- Observe lamp/LED glow.
- Record results.

Question 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.

Accepted Answer

No, the lamp will not glow because the cells are not connected in series correctly.
Correct connection:
- Connect the positive terminal of the first cell to the negative terminal of the second cell.
- Connect the LED terminals such that the longer wire (positive) connects to the positive terminal of the first cell and the shorter wire (negative) connects to the negative terminal of the second cell.

Explanation: For the LED to glow, the two cells must be connected in series to provide sufficient voltage and correct polarity must be maintained. — Step-by-step:
- Identify incorrect wiring in the figure.
- Connect cells in series: positive to negative.
- Connect LED with correct polarity.
- Complete the circuit to allow current flow.

Question 12

Which of the following is NOT a common use of electricity listed under the 'Cooking' category?

Accepted Answer

Refrigerator — Refrigerator is categorized under 'Heating and Cooling' uses of electricity, not under 'Cooking'. Electric kettle, toaster, and mixer grinder are common cooking appliances that use electricity.

Question 13

Why is it advised to use only batteries or cells for electrical experiments at home or school instead of the power supply from mains or portable generators?

Accepted Answer

Batteries or cells provide a safe and low voltage source of electricity, reducing the risk of electric shock or injury. Power supply from mains or generators carries high voltage and can be dangerous if not handled properly. — Electricity from mains or portable generators is high voltage and can cause serious injuries or even death if mishandled. Batteries and cells supply low voltage electricity, making them safer for experiments. Hence, using batteries or cells helps prevent accidents during electrical experiments.

Question 14

What are the two terminals of an electric cell called and how can you identify them physically?

Accepted Answer

The two terminals of an electric cell are called the positive (+) terminal and the negative (–) terminal. The positive terminal is usually a small protruding metal cap, while the negative terminal is a flat metal disc. — Every electric cell has two terminals. The positive terminal is marked with a plus (+) sign and is the protruding metal cap. The negative terminal is marked with a minus (–) sign and is the flat metal disc. This physical difference helps identify the terminals for correct connections.

Question 15

How are two or more electric cells connected to form a battery, and why is this done?

Accepted Answer

Two or more electric cells are connected in series by joining the positive terminal of one cell to the negative terminal of the next. This is done to provide more electrical energy or longer usage time for devices. — Connecting cells in series increases the total voltage supplied to the circuit, allowing devices to operate for longer or with more power. This combination of cells is called a battery. The positive terminal of one cell connects to the negative terminal of the next to maintain correct polarity.

Electricity

Electricity — Study Notes

Electricity: Circuits and their Components

3.1 A Torchlight

3.2 A Simple Electrical Circuit

Practice Questions — Electricity

All 12 Chapters in Curiosity