NCERT Solutions Curiosity Chapter 3 –40Interdisciplinary — Exploratory Projects

Book page 39 Updated on2026-09-05

Q1.
Suppose that due to some problem, the power supply is disrupted in your area for two days. List out which actions from your daily life you would not be able to do.
Answer

Go through one ordinary day, hour by hour, and mark everything that needs electricity. That is the honest way to make this list.

Sample answer — a list for two days without power:

Time of dayWhat I would not be able to do
MorningPump water to the overhead tank, use the geyser for a hot bath, grind masala in the mixer, toast bread, iron the school uniform, get news from TV
School / work hoursUse fans and lights in the classroom, use a computer or projector, charge a phone, use the lift, run the school water cooler
EveningSwitch on lights to study, run the fan or cooler, watch TV, use the washing machine, use the electric sewing machine
NightKeep milk and vegetables cold in the refrigerator, use street lights while walking, charge the emergency lamp
Any timeDraw money from an ATM, get a photocopy, use a shop's card machine, use a water purifier

What still works — anything that runs on cells or batteries: a torch, a wall clock, a wrist watch, a mobile phone until its battery runs out, a radio with cells. This is exactly why the chapter calls a cell a portable source of electrical energy.

Try This: Also note down what you would do instead — study by daylight, cook on a gas stove, store water in buckets. A good project compares 'what stops' with 'how people manage'.
Q2.
Using a solar panel (Fig. 3.22a) as a source of electrical energy, make a circuit to run a toy fan (Fig. 3.22b) as shown in Fig. 3.22c.
Answer

The solar panel simply takes the place of the cell or battery — everything else you have learnt about circuits stays the same.

What you need: a small solar panel, a toy fan (a small motor with a plastic blade), two connecting wires with the ends stripped, and bright sunlight.

How to do it:

  1. Find the two terminals of the solar panel; they are usually marked + (red wire) and (black wire).
  2. Join one terminal of the panel to one terminal of the toy fan's motor with a connecting wire.
  3. Join the other terminal of the panel to the other terminal of the motor. The loop is now complete.
  4. Hold the panel flat in bright sunlight. The fan starts turning.
  5. Now cover the panel with your hand or a piece of cardboard. The fan slows down and stops — proof that the panel, not the wire, is the source.

Things worth observing and writing in your report:

  • The fan runs fastest when the panel faces the Sun squarely, and slows down when the panel is tilted or shaded.
  • If you interchange the two wires, the fan turns the other way — the motor reverses because the direction of current has reversed.
  • The fan does not run indoors under an ordinary bulb, or runs very slowly — sunlight is far stronger than room light.
Why it happens: A solar panel changes the energy of sunlight directly into electrical energy, just as a cell changes chemical energy into electrical energy. Both give a direct current (DC), which is why the same simple circuit works with either.
Q3.
Visit an electrical items shop. With the help of the shopkeeper, identify the various types of cells available. For each cell, also find out which device(s) it is used for. Prepare a report.
Answer

Carry a notebook, ask the shopkeeper to show you each type, and note its shape, size, marking and use. Do not touch or open any cell.

Sample report — cells commonly found in a shop:

Type of cellWhat it looks likeDevices it is used in
AA (pencil cell)Cylindrical, about 5 cm longTorch, wall clock, TV remote, toys
AAACylindrical, thinner and shorter than AASmall remotes, computer mouse, digital thermometer
C and D cellsThick cylindersBig torches, emergency lamps, transistor radios
9 V batterySmall rectangular block with two studs on topMultimeters, smoke alarms, small experiment kits
Button cellFlat and round like a coinWrist watches, hearing aids, calculators, car keys
Rechargeable battery (Li-ion)Flat pack or cylinder, marked 'rechargeable'Mobile phones, laptops, power banks, electric vehicles
Lead-acid batteryLarge, heavy box with two thick terminalsCars, inverters at home

Also find out and write about: the voltage printed on each cell (1.5 V on most pencil cells, 9 V on the block, 3 V on many button cells), the price, how long it lasts, and which of them can be recharged.

Did you know? Used cells should never be thrown into ordinary dustbins. The chemicals inside can harm soil and water, so they must go to a battery-collection or e-waste bin. Add a line about this in your report.
Q4.
Prepare a list of objects in your home under three categories: (i) Objects which are electrical insulators only (ii) Objects which are electrical conductors only (iii) Objects which are made of both, whose some parts are insulators and some electrical conductors
Answer

Walk through the house and ask one question for each object: what material is it made of? Then place it in the right column.

Sample answer:

(i) Insulators only(ii) Conductors only(iii) Both parts together
Plastic bucketSteel spoonScrewdriver — metal rod with a plastic handle
Wooden chair, wooden rulerIron nail, safety pinElectric wire — copper inside, plastic outside
Glass tumbler, glass bangleAluminium foil, copper coinPlug top — brass pins in a plastic body
Rubber eraser, rubber slipperBrass lock, steel scaleTorch — metal contacts inside a plastic body
Candle, cotton cloth, paper, ceramic cupIron key, steel plateSwitch board, iron (press) with plastic handle, pressure cooker with bakelite handles
Why it happens: Category (iii) is the most interesting one. Wherever we must use electricity but also touch the device, the designer puts a conductor where the current has to go and an insulator where our hand has to go. A screwdriver used by an electrician, a plug top and an electric wire are all built on that one idea.
Try This: Pick up any object from column (iii) and mark with your finger exactly where the conductor ends and the insulator begins. That boundary is what keeps the user safe.
Was this helpful? Report an error