1. Helping Nihal – uses of electricity
Q 1 (a). Fill the blank lines in Nihal’s lists.
| Heading | Some more items you can write |
|---|---|
| Entertainment | Video game console, music player |
| Communication | Land-line phone, e-mail device |
| Lighting | LED bulb, emergency lamp |
| Cooking | Electric rice-cooker, sandwich-maker |
| Transportation | Electric bicycle, airport escalator |
| Heating & Cooling | Water cooler |
| Others | Washing-machine |
Q 1 (b). Suggest other ways to group the uses of electricity.
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Home use, School use, Hospital use, Factory use, Farming use.
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Or by Tiny devices (watch), Medium devices (TV), Big machines (train).
2. Activity 3.1 – Torchlight switch
Q 2. Why does the torch lamp glow in only one switch position?
Because in that position the switch closes the metal path inside the torch.
A closed path lets electric current travel from the battery through the lamp and back, so it glows. In the other position the path is broken, so no current flows.
3. Activity 3.3 – Order of cells in a torch
Q 3. Are the cells placed in any special order?
Yes. The positive end of one cell always touches the negative end of the next cell.
This head-to-tail order makes a battery, giving the lamp the right amount of energy.
4. Activity 3.4 – Incandescent lamp
Q 4 (a). Which part of the lamp glows?
The very thin wire inside the glass bulb, called the filament, glows.
Q 4 (b). How is the filament fixed?
The filament is held up by two thicker support wires.
One support joins the metal tip at the base, the other joins the metal side case. They keep the two terminals apart.
5. Activity 3.5 – LED observation
Q 5 (a). Do you see any filament inside an LED?
No, LEDs have no filament.
Q 5 (b). Do you find one wire longer than the other?
Yes. The long wire is the positive terminal and the short wire is the negative terminal.
6. Activity 3.6 – Making the lamp glow (Table 3.1)
Q 6. In which arrangements does the lamp glow?
| S. No. | Lamp glows? | Why |
|---|---|---|
| 1 | Yes | Complete path, opposite battery terminals joined to lamp terminals |
| 2 | No | Only one battery terminal reached lamp, path broken |
| 3 | No | Both lamp wires touch the same battery side, no full loop |
| 4 | No | Gap in circuit |
| 5 | No | Same reason as S. 3 |
| 6 | Yes | Same as S. 1 – full closed circuit |
The lamp only glows when the circuit is closed and each lamp terminal meets a different battery terminal.
7. Activity 3.7 – Positive end of a two-cell battery
Q 7. How do you know which holder terminal is positive?
Follow the strip inside the holder: the terminal that touches a cell’s protruding cap ( + ) is positive; the terminal that touches the flat end ( – ) is negative.
8. Activity 3.7 – LED polarity test
Q 8. Does the LED glow in both wire arrangements?
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First arrangement (battery + to long LED wire): LED glows.
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Second arrangement (wires swapped): LED does not glow.
Current can pass through an LED in one direction only.
9. Activity 3.8 / 3.9 – How a switch works
Q 9. How does a switch turn the torch on or off?
A switch is just a tiny metal bridge.
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ON position: bridge touches both side plates – circuit closes – current flows – lamp shines.
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OFF position: bridge lifts off – gap opens – no current – lamp is dark.
10. Activity 3.10 – Circuit‐diagram drawing
Q 10. Are your circuit diagrams like Fig 3.14 (a) and (b)?
Yes. Using symbols makes the same neat diagrams for both the bulb circuit and the LED circuit.
11. Activity 3.11 – Conductors and insulators (Table 3.3)
Q 11. Which objects conduct electricity and which do not?
| Object tested | Lamp glows? | Conclusion |
|---|---|---|
| Metal key | Yes | Conductor |
| Aluminium foil | Yes | Conductor |
| Sewing needle | Yes | Conductor |
| Plastic scale | No | Insulator |
| Rubber eraser | No | Insulator |
| Candle wax | No | Insulator |
| Wooden stick | No | Insulator |
| Paper strip | No | Insulator |
| Glass bangle | No | Insulator |
Metals conduct; plastic, rubber, wood, glass, wax and paper do not.
12. In-text questions on wires
Q 12 (a). Why do we use metal for wires?
Because metals let electric current pass easily.
Q 12 (b). Why are the wires covered with plastic or rubber?
Plastic and rubber are insulators. The covering stops current escaping and protects people from electric shock.
13. Difference between battery electricity and wall-socket electricity
Q 13. How is electricity from a battery different from wall-socket electricity?
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Battery gives Direct Current (DC) – steady one-way flow – good for small gadgets.
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Wall socket gives Alternating Current (AC) – current changes direction many times a second – powerful enough for big home appliances.
LET US ENHANCE OUR LEARNING – Exercise Answers
1. Choose the incorrect statement.
(i) “A switch is the source of electric current …” is incorrect.
A switch only opens or closes a path; the cell/battery is the source.
2. In Fig 3.16, with which material between A and B will the lamp not glow?
With any insulator such as plastic, rubber or wood the lamp will not glow, because current cannot pass.
3. In Fig 3.17, if one filament breaks, will the other lamp glow? Why?
No. The two lamps are in the same series path. A broken filament opens the circuit; no current flows through the other lamp.
4. Student left the plastic on the connecting wires. Will the lamp glow?
No. The plastic keeps the metals apart, so current cannot pass.
5. Draw a circuit diagram for a simple torch.
(Verbal description) Draw: Battery symbol → switch symbol → lamp symbol → back to battery. Battery long line is +, short is –.
6. Refer Fig 3.18
| Switch positions | Lamp(s) that glow | Reason |
|---|---|---|
| (i) S2 ON, S1 OFF | L2 glows | Circuit closed only for L2 |
| (ii) S2 OFF, S1 ON | L1 glows | Circuit closed only for L1 |
| (iii) Both ON | Both L1 and L2 glow | Both paths closed |
| (iv) Both OFF | None glow | Whole circuit open |
7. Vidyut’s lamp does not glow (Fig 3.19). List possible reasons and checks.
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Cells the wrong way round → turn them.
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Cells exhausted → test with known good bulb.
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Wires loose or broken → press connections.
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Plastic not scraped from wire ends → remove plastic.
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Lamp filament fused → replace lamp.
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Switch open or faulty → close or change switch.
8. Fig 3.20 – cases where lamp will not glow when switch is closed:
The lamp will not glow in (b) and (d) because the wires in those cases do not give a full path (either both wires touch the same battery side or a gap still exists).
9. Battery markings are rubbed off. How to find + and – ?
Use a small LED and a resistor:
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Connect LED one way; if it lights, the leg on the glowing side is at the positive terminal.
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If it stays dark, swap leads; when it lights you have found the + side.
10. Six cells (A-F) – design a test to find which work.
(i) Items needed) small bulb, two short wires, some tape.
(ii) Procedure) Touch one wire to bulb base, the other to bulb side. Press a cell between free wire ends. If bulb lights, cell works. Test all six.
(iii) Activity) After testing you can list working cells: e.g., “A, C and E worked; B, D, F did not.”
11. Fig 3.21 – Will Tanya’s LED glow? If not, draw correct wires.
It will not glow because the two cells are not in series.
Correct drawing: connect the positive of cell 1 to negative of cell 2; take the free positive end to long LED leg, take the free negative end to short LED leg.
14. Exploratory-project starter (power cut)
(Open task – no single right answer, so only a hint given)
If power fails for two days, fans, lights, fridge, internet modem, phone charger, TV, mixer, lift, water pump and many other daily actions stop.