RBSE Solutions Class 7 Science Chapter 3 The Electricity Circuits and Their Components

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Question 1. Choose the incorrect statement.
(i) A switch is the source of electric current in a circuit.
Answer: The statement "(i) A switch is the source of electric current in a circuit" is incorrect. A switch does not produce electric current; its job is to either complete (turn on) or break (turn off) the flow of current in a circuit. Batteries or power outlets are the actual sources of electric current. Without a power source, the switch would have nothing to control.
In simple words: A switch only starts or stops electricity, it doesn't make the electricity itself.

🎯 Exam Tip: Understand the basic function of each circuit component. A switch controls flow, a battery provides power, and a lamp shows the effect of current.

Question 2. Observe Fig. 3.16. With which material connected between the end A and B, the lamp will not glow?
Answer: If any material that is an insulator of electricity is connected between points A and B, the lamp will not glow. Insulators do not allow electric current to pass through them. Common examples of such materials include wood, rubber, plastic, and glass.
In simple words: If you put something that stops electricity, like wood or plastic, between A and B, the light won't turn on.

🎯 Exam Tip: Remember the difference between conductors (allow current) and insulators (block current). This concept is key to understanding how circuits work.

Question 3. In Fig. 3.17, the filament of one of the broken, will the other glow? Justify your answer.
Answer: If the lamps are connected in a series circuit, and the filament of one lamp breaks, then the other lamp will not glow. This is because a series circuit is like a single path for electricity; if one part breaks, the entire path is interrupted, stopping the current flow to all components. However, if the lamps were connected in a parallel circuit, the other lamp would continue to glow even if one filament was broken, as parallel circuits provide multiple paths for the current.
In simple words: If lights are in a single line (series) and one breaks, all go out. If they are side-by-side (parallel), the other lights stay on.

🎯 Exam Tip: Differentiate between series and parallel circuits. In series, all components share one path; in parallel, they have independent paths.

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?
Answer: No, the lamp will not glow. The insulating cover on the wires stops the electric current from flowing through the circuit. For the lamp to glow, the circuit needs to be complete and made of conducting materials, allowing electricity to pass from the cell through the lamp and back to the cell. Removing the insulator exposes the conductor inside, which is needed to connect the circuit properly.
In simple words: The lamp won't light up. The plastic on the wire stops electricity, so the circuit can't be completed.

🎯 Exam Tip: Always ensure that connecting wires have their insulation removed at the contact points to create a proper electrical connection.

Question 6. In Fig. 3.18:
(i) If S2 is in 'ON' position, S( 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?
Answer:
(i) If S2 is 'ON' and S₁ is 'OFF', then both lamps L₁ and L2 will not glow because the circuit is still open at S₁. To complete the circuit, both switches need to be in the 'ON' position.
(ii) If S2 is 'OFF' and S₁ is 'ON', then both lamps L₁ and L2 will not glow. The circuit remains open at S2, preventing current flow.
(iii) If S₁ and S2 both are 'ON', then both L₁ and L2 lamps will glow. When both switches are closed, the circuit becomes complete, allowing current to flow through both lamps.
(iv) If both S₁ and S2 are 'OFF', then none of the lamps will glow, as the circuit is broken at two points, blocking any current.
In simple words: Both switches need to be turned on for the lights to work. If even one switch is off, the lights stay off because the power path is broken.

🎯 Exam Tip: In a series circuit with multiple switches, all switches must be closed (ON) for current to flow and for the components to operate.

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?
Answer: There can be several reasons why the lamp might not glow even after closing the circuit:
(i) The battery or cells might be faulty or discharged, meaning they have no power left to supply.
(ii) The filament of the lamp could be broken, which prevents electricity from heating it up to produce light. Always check if the bulb is intact.
(iii) The switch itself might not be working correctly, failing to complete the circuit when turned 'ON'.
(iv) The insulated covers on the connecting wires might not have been fully removed, blocking the electrical connection.
(v) There could be a loose or broken joint in the connections, stopping the current from flowing smoothly.
(vi) A wire might be broken somewhere within the circuit, creating an open path.

Methods to find out the fault:
(i) Systematically change each component of the circuit one by one. Replace the cell, then the switch, then the wires, and finally the lamp, testing the circuit after each change to see which part was faulty.
(ii) Check the cell or lamp with alternative, known-good components to see if they work.
(iii) Carefully check all connections and wires to make sure they are tight and unbroken.
(iv) Test the switch by repeatedly turning it 'ON' and 'OFF' to ensure it is making and breaking the connection correctly.
In simple words: The light isn't working because the battery is dead, the bulb is broken, the switch isn't working, wires are not connected well, or a wire is broken. To fix it, check each part of the circuit one by one until you find the problem.

🎯 Exam Tip: When troubleshooting a circuit, always test components systematically, starting with the power source, then the switch, and finally the load (lamp).

Question 8. In Fig. 3.20, in which case(s) the lamp will not glow when the switch is closed?

🎯 Exam Tip: For circuit diagrams involving LEDs, always check the polarity of the connection. LEDs are diodes and only allow current to flow in one direction, from the positive to the negative terminal.

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 ill follow.
(iii) With the items, carry out the activity to identify the cells that are working.
Answer:
(i) Required items: A small bulb (lamp), two pieces of connecting wire, and a bulb holder (if available). A testing board can also be helpful.
(ii) Method: Connect both ends of one wire to the two terminals of the cell. Then, connect the ends of the bulb holder's wires to the free ends of the cell wires, completing a simple circuit. This setup allows the current to flow through the bulb.
(iii) Check with all cells one by one: If the bulb glows when connected to a particular cell, that cell is working. If the bulb does not glow, that cell is not working. The activity should be carried out carefully, making sure all connections are firm.
In simple words: To find which cells work, use a small light bulb and two wires. Connect the wires from the bulb to a cell. If the bulb lights up, the cell works. If not, the cell is dead. Do this for each cell.

🎯 Exam Tip: Always use a simple, reliable test circuit when checking components. A small bulb is a good indicator for current flow from a cell.

Question 11. 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.
Answer: No, the LED lamp will not glow in the circuit shown. This is because both ends of the LED are connected to the positive ends of the two cells, which are incorrectly configured for an LED. An LED (Light Emitting Diode) is a type of component that only allows electric current to pass through it in one specific direction. For an LED to glow, its positive terminal (anode) must be connected to the positive end of the battery, and its negative terminal (cathode) must be connected to the negative end of the battery. The two cells need to be connected in series correctly (positive to negative) to provide sufficient voltage, and then the LED must be connected with the correct polarity.
In simple words: The LED won't light up because it's connected the wrong way around. LEDs only let electricity go one way, so you must connect the positive side of the LED to the positive side of the battery, and the negative side of the LED to the negative side of the battery.

🎯 Exam Tip: LEDs are sensitive to polarity. Always connect the longer lead (anode, positive) to the positive supply and the shorter lead (cathode, negative) to the negative supply.

Electricity Circuits and Their Components Class 7 Questions and Answers (Intext)

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Question 1. Why does the torch lamp glow in one position of its switch?
Answer: The torch lamp glows in one position of its switch because that position (the 'ON' position) completes the electric circuit. When the circuit is complete, electric current can flow through the lamp's filament. This current heats the filament, making it glow and produce light. When the switch is in the 'OFF' position, it breaks the circuit, stopping the current flow and preventing the lamp from glowing.
In simple words: The torch light turns on when the switch completes the circle for electricity to flow, making the tiny wire inside hot and bright.

🎯 Exam Tip: For a lamp to glow, the electric circuit must be closed, allowing a continuous path for the electric current.

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Question 2. How does a switch turn on or off the torchlight?
Answer: A switch is a simple device that controls the flow of electricity in a circuit. In its 'ON' position, the switch closes the circuit, creating a continuous path for electric current to flow through the torchlight, which then helps it glow. In its 'OFF' position, the switch opens or breaks the electric circuit. This stops the flow of electric current, so the lamp in the torchlight does not glow. It acts like a gate for electricity.
In simple words: A switch turns the light on by closing the electric path, letting electricity flow. It turns the light off by opening the path, stopping the electricity.

🎯 Exam Tip: Think of a switch as a simple gate. When the gate is closed (ON), current flows; when open (OFF), current stops.

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Question 3. Can we represent the circuits in a simpler manner?
Answer: Yes, electric circuits can definitely be represented in a much simpler manner using standard symbols. These symbols make it easier to draw and understand complex circuits without having to sketch realistic pictures of each component. For example, in the symbol for an electric cell, a long line represents the positive terminal, while a shorter, thicker line represents the negative terminal. Other components like lamps, switches, and wires also have their own specific symbols.
In simple words: Yes, we can draw circuits using simple symbols instead of real pictures. Like a long line means positive, and a short line means negative for a battery.

🎯 Exam Tip: Learning standard circuit symbols is essential for reading and designing electrical diagrams efficiently.

Question 5. Why are electric wires covered with plastic or rubber?
Answer: Electric wires are covered with plastic or rubber because these materials are insulators. Insulators do not allow electric current to flow through them. This covering prevents the electricity from escaping the wire and stops us from getting electric shocks if we accidentally touch the wire. It also stops wires from touching each other and causing short circuits. The insulation is crucial for safety and proper functioning of electrical systems.
In simple words: Wires have plastic or rubber covers to keep us safe from electric shocks and to stop electricity from leaking out or causing problems.

🎯 Exam Tip: Always handle electrical wires carefully and ensure the insulation is intact to prevent accidents and ensure circuit integrity.