NCERT Solutions Curiosity Chapter 10 Extension tasks — Discover, design, and debate

Book page 169 Updated on2026-09-05

Q1.

Visit a nearby hospital or the clinic of an ENT specialist, or a dentist, with your teacher or parents. Request the doctor to show you the mirrors used for examining ear, nose, throat, and teeth. Identify the kind of mirror used in these instruments.

Answer

How to do it. Fix the visit through your teacher. Carry a notebook and, for each instrument you are shown, record three things: the shape of the reflecting surface seen edge-on, whether the image of a small object held close to it looks bigger or smaller, and what the doctor uses that instrument for.

What you will find.

Instrument	Kind of mirror	Why that kind
Dental mirror (mouth mirror)	Concave	Held close to a tooth it gives an erect, enlarged view, so a small cavity can be seen clearly. Its long handle also lets the dentist see the back of a tooth.
ENT head mirror worn on the forehead	Concave, with a small hole at its centre	It converges light from a lamp behind the patient onto the ear, nose or throat, lighting up a deep, narrow space. The doctor looks through the central hole along the same line as the light.
Small laryngeal / examination mirror on a stem	Plane or slightly concave	It is used mainly to turn the line of sight round a corner, into the throat; a plane surface keeps the view undistorted.

The common idea: in medical instruments a concave mirror is chosen when light has to be gathered into a dark cavity or a small structure has to be magnified. Where the mirror is only needed to look round a corner, a plane surface is better, because it does not change the size of what the doctor sees.

Tip: ask the doctor why the head mirror has a hole in the middle. It is the neatest example in the whole chapter of light being sent one way and viewed along the same line.

Q2.

Harnessing sunlight is key to solving future energy challenges. In devices like solar cookers (Fig. 10.29), mirrors are used to converge sunlight and generate heat. In India, such designs are used in villages, thus saving electricity and reducing fossil fuel use. Think of a design for a solar cooker for your school or home and prepare a detailed proposal for it including the budget required.

Answer

What a good proposal must contain: (1) the need it meets, (2) the physics it uses, (3) a labelled design with dimensions, (4) a materials-and-cost table, (5) how you will test it, and (6) its limitations.

Sample proposal — a box-type solar cooker with a plane reflector for the school kitchen

1. Need. The school heats water and cooks pulses for the midday meal on an LPG stove. A solar cooker used on the roughly 250 clear days in a year can take over part of that work and cut both the gas bill and the fuel used.

2. Physics used. A hinged plane mirror lid reflects an extra beam of sunlight into the box, so the food gets sunlight from two directions instead of one. A blackened inner surface absorbs that light and turns it into heat, and a double glass cover lets sunlight in but traps the warm air, so the temperature inside climbs to about 100–120 °C.

3. Design. Outer wooden box 60 cm × 60 cm × 20 cm; inner aluminium tray 50 cm × 50 cm painted matt black; 5 cm of thermocol or glass wool between the two as insulation; two glass sheets 4 mm thick, 2 cm apart, as the lid; a plane mirror 60 cm × 60 cm hinged to the lid, propped so that the reflected sunlight falls into the box; four black-painted aluminium cooking pots with lids.

Item	Specification	Estimated cost (₹)
Wooden outer box	60 × 60 × 20 cm, plywood	1200
Aluminium inner tray	50 × 50 cm	700
Insulation	Thermocol / glass wool, 5 cm	300
Double glass lid	2 sheets, 4 mm	600
Plane mirror + hinges	60 × 60 cm	800
Black paint, sealant, screws	—	400
Four cooking pots	Aluminium, blackened, with lids	600
Thermometer (0–150 °C)	For testing	200
Total		4800

4. Testing. Record the inside temperature every 15 minutes from 10 a.m. to 3 p.m. on a clear day, with and without the mirror lid open, and plot the two curves. Then time how long the cooker takes to cook 500 g of rice, and compare the LPG saved with the cost of the cooker to find how many months it takes to pay for itself.

5. Limitations, stated honestly. It does not work on cloudy days or after about 3 p.m.; it cannot fry; and the cooker must be turned every hour or so to keep facing the Sun.

Why a plane mirror is enough here, and why a big cooker would need a concave one: a box cooker only has to add one more beam of sunlight to a wide box, and a plane mirror does that without needing to be aimed precisely. To reach the far higher temperatures needed for frying — or, on a large scale, for a solar furnace — the sunlight must be brought to a point, and only a concave (converging) reflector can do that.

Q3.

Use online tools or animation to do virtual experiments with spherical mirrors and lenses. Move objects in the simulation and observe how the image changes.

Answer

How to use a simulation well. A simulation is only useful if you go into it with a question. Set one before you start, change one thing at a time, and write down the numbers — not just the picture.

A set of runs worth doing

Run	What to change	What to record
1	Concave mirror; move the object slowly in from far away	The object distance at which the image flips from inverted to erect
2	Concave mirror; object very far away	Where the image forms — it should be at the focus
3	Convex mirror; move the object from near to very far	Whether the image ever becomes inverted or larger (it should not)
4	Convex lens; repeat run 1	Compare the flip distance with the concave mirror's
5	Concave lens; repeat run 3	Whether the image stays erect and diminished throughout
6	Any mirror; change the curvature, keep the object fixed	How the image size changes when the mirror is made deeper

What you should be able to conclude. The concave mirror and the convex lens behave alike, and the convex mirror and the concave lens behave alike. In each pair the difference lies only in whether the light is reflected or transmitted; what decides the image is whether the rays are made to converge or to diverge.

Tip: keep the ray display switched on in the simulation. Watching where the rays cross — or fail to cross — explains the image far better than watching the image alone.

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