Class 7 General Science – Unit 3: Electric Circuits and their Components (Pages 76–118) – Textbook Solutions & Answers. This post covers complete AP SCERT Class 7 Science Unit 3 "Electric Circuits and their Components" textbook answers, including electric cell, battery, electric lamp (incandescent & LED), electric switch, circuit diagrams, series and parallel circuits, electrical conductors and insulators. These CBSE/AP State Syllabus Class 7 Science solutions are useful for students preparing for FA/SA exams, APTET, and DSC General Science candidates looking for concept-based Q&A. Keywords: Class 7 Science Unit 3 answers, Electric Circuits notes, AP SCERT Science solutions, series and parallel circuit, conductors and insulators class 7.
📘 Unit 3: Electric Circuits and their Components
Let us Enhance our Learning (Page 110–118)
Question 1 (Page 110)
Which of these symbols is used for a battery in a circuit?
A: P B: Q C: R D: S
Answer: D) S
The symbol S shows two pairs of long-short lines (⊣⊢), which represents a battery (a combination of two or more cells). A single cell is shown with only one pair of long-short lines.
Question 2 (Page 112)
Observe the circuit shown in Fig. 3.19. The switch is open. What will happen to the bulb?
Answer: C) The bulb does not glow because the circuit is incomplete.
When the switch is open, there is a gap in the path, so current cannot flow, and the bulb does not glow.
Question 3 (Page 112)
Choose the incorrect statement.
Answer: (i) A switch is the source of electric current in a circuit — This statement is INCORRECT.
A switch does not produce or supply current; it only completes or breaks the path of the circuit. The electric cell/battery is the actual source of electric current.
Question 4 (Page 112)
Ravi wants to check whether a key made of a new material conducts electricity...What can Ravi correctly conclude?
Answer: B) The key is an insulator, and the iron nail is a conductor.
Since the bulb did not glow with the key, current could not pass through it, so the key is an insulator. When the iron nail was used, the bulb glowed, showing that current passed through it — hence the iron nail is a conductor.
Question 5 (Page 112)
Define the following:
| Term | Definition |
|---|---|
| a) Electric conductors | Materials through which electric current can flow easily are called electric conductors (e.g., copper, iron, aluminium). |
| b) Insulators | Materials through which electric current cannot pass are called insulators (e.g., rubber, plastic, wood). |
| c) Electric cell | A portable source of electrical energy having two terminals — a positive (+ve) terminal and a negative (–ve) terminal. |
| d) Switch | A simple device that either completes (ON) or breaks (OFF) an electric circuit. |
| e) Circuit diagram | A representation of an electrical circuit drawn using standard symbols for its components. |
Question 6 (Page 112)
Observe Fig. 3.20. With which material connected between the ends A and B, the lamp will not glow?
Answer: The lamp will not glow if an insulating material such as a plastic strip, rubber band, wooden piece, or a piece of glass is connected between points A and B, because insulators do not allow electric current to pass through them.
Question 7 (Page 112)
Suppose the '+' and '–' symbols cannot be read on a battery. Suggest a method to identify the two terminals of this battery.
Answer: We can connect an LED to the battery using two wires. Since an LED glows only when its longer wire (positive terminal) is connected to the positive terminal of the battery, we can try connecting the LED in both directions. The terminal connected to the longer wire of the LED when it glows is the positive terminal, and the other one is the negative terminal.
Question 8 (Page 112)
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 plastic/rubber covering on the wires is an insulator and does not allow electric current to pass through it. Since the metal part of the wire is not in contact with the circuit components, the circuit remains incomplete, so the lamp will not glow.
Question 9 (Page 114)
In Fig. 3.21, lamps L₁ and L₂ are connected with switches S₁ and S₂ in a single loop along with the battery.
| Condition | Which lamp(s) glow? |
|---|---|
| (i) S₂ ON, S₁ OFF | No lamp glows (circuit is broken at S₁) |
| (ii) S₂ OFF, S₁ ON | No lamp glows (circuit is broken at S₂) |
| (iii) S₁ and S₂ both ON | Both L₁ and L₂ glow (circuit is complete) |
| (iv) Both S₁ and S₂ OFF | No lamp glows (circuit is broken at two points) |
Reason: L₁, S₂ and L₂ are connected in a single series path with S₁ and the battery. Since it is a series circuit, both switches must be ON for current to flow and for the lamps to glow.
Question 10 (Page 114)
Ramu has made the circuit as shown in Fig. 3.22. Even after closing the circuit, the lamp does not glow. What can be the possible reasons? What will you do to find out why the lamp did not glow?
Possible reasons:
- The filament of the lamp may be broken (fused/damaged bulb).
- The cell may be dead or fully discharged.
- The connecting wires may be loose or broken internally.
- The insulating covering may not be properly removed from the wire ends.
- The switch may not be making proper contact.
- The lamp may not be fixed properly in its holder.
To find out the reason: Test each component separately using a working tester circuit (a known good cell and lamp) — check the cell, check the lamp, check the switch, and check each wire connection one by one until the faulty part is found.
Question 11 (Page 114)
In Fig. 3.23, in which case(s) the lamp will not glow when the switch is closed?
(a) and (b) – The incandescent lamp will glow in both cases when the switch is closed, since it does not matter which terminal of the incandescent lamp is connected to which terminal of the cell.
(c) – The LED is connected correctly (positive terminal of LED to positive terminal of cell), so it will glow.
(d) – The LED is connected in the reverse direction, so it will NOT glow, since current can pass through an LED in one direction only.
Question 12 (Page 114)
An LED requires two cells in series to glow. Ramya made the circuit as shown in Fig. 3.24. Will the lamp glow? If not, draw the wires changed for correct connections.
Answer: No, the LED will not glow. In Fig. 3.24, both cells are placed with their positive terminals on the same side, so the positive terminal of one cell is NOT connected to the negative terminal of the other. This does not form a proper battery.
Correction: The cells should be placed so that the positive terminal of one cell touches the negative terminal of the next cell (as in Fig. 3.3). Then the free positive terminal of the battery should be connected to the longer wire (positive) of the LED, and the free negative terminal should be connected to the shorter wire (negative) of the LED.
Question 13 (Page 116)
In Fig. 3.25, if the filament of one of the lamps is broken, will the other glow? Justify your answer.
Answer: No, the other lamp will also not glow.
Justification: The two lamps in Fig. 3.25 are connected in a series connection — they are on a single path for current to flow. If the filament of one lamp breaks, it creates a gap in that single path, making the circuit open (incomplete). Since there is no other path for the current, the second lamp also does not receive any current and will not glow.
Question 14 (Page 116)
Draw a circuit diagram for a simple torch using symbols for electric components.
Circuit: Cell → Switch → Lamp → back to Cell (all connected in a single closed loop).
Question 15 (Page 116)
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) Items required: A working torch lamp, a lamp holder, a cell holder, two connecting wires, and the six cells A, B, C, D, E, F.
(ii) Procedure:
- Fix the lamp in the lamp holder and connect it to the cell holder using two wires, keeping the cell holder empty — this is our tester circuit.
- Place cell A in the cell holder, taking care that the negative terminal touches the spring side.
- Observe whether the lamp glows or not. Note the observation.
- Remove cell A and repeat the same steps one by one for cells B, C, D, E, and F.
- Record the results (glow / no glow) for each cell in a table.
(iii) Observation table:
| Cell | Lamp glows (Yes/No) | Conclusion |
|---|---|---|
| A | To be observed | Working / Not working |
| B | To be observed | Working / Not working |
| C | To be observed | Working / Not working |
| D | To be observed | Working / Not working |
| E | To be observed | Working / Not working |
| F | To be observed | Working / Not working |
Cells for which the lamp glows are working cells; cells for which the lamp does not glow are not working (dead) cells.
Question 16 (Page 116)
Draw a neat diagram using a battery, lamp, LED, toy motor and switch in series and parallel connections.
Exploratory Projects (Page 116–118)
1. Power supply disrupted for two days — daily activities affected: Charging mobile phones, using fans/lights, watching TV, using the fridge, using the water pump/motor, using the washing machine, using computers/internet, and using electric induction stoves would all not be possible.
2. Using a solar panel to run a toy fan: Connect the two wires of the solar panel to the two terminals of the toy fan motor as shown in Fig. 3.26c. When sunlight falls on the solar panel, it generates electricity, which passes through the wires and makes the toy fan run.
3. Visit to electrical shop: Common types of cells found are AA cells, AAA cells, button cells, and 9V batteries — used in remotes, torches, wall clocks, watches, hearing aids, and toys respectively.
4. List of household objects:
| Insulators only | Conductors only | Both (insulator + conductor parts) |
|---|---|---|
| Wooden chair, plastic mug, rubber slipper, glass tumbler | Steel spoon, iron key, copper coin, aluminium vessel | Electric wire, scissors, screwdriver, plug top |
— End of Unit 3: Electric Circuits and their Components (Class 7 General Science, AP SCERT) —
