List of top Science Questions

Light enters from air to glass having refractive index 1.50. What is the speed of light in the glass? The speed of light in vacuum is 3 × 10⁸ m s⁻¹.

A ray of light travelling in air enters obliquely into water. Does the light ray bend towards the normal or away from the normal? Why?

A concave mirror produces three times magnified (enlarged) real image of object placed at 10 cm in front of it. Where is the image located?

Find the focal length of a convex mirror whose radius of curvature is 32 cm.

Why do we prefer a convex mirror as a rear-view mirror in vehicles?

Name the mirror that can give an erect and enlarged image of an object.

The radius of curvature of a spherical mirror is 20 cm. What is its focal length?

Define the principal focus of a concave mirror.

A copper wire has diameter 0.5 mm and resistivity of \(1.6×10^{–8} \ Ω m\). What will be the length of this wire to make its resistance 10 Ω? How much does the resistance change if the diameter is doubled?

The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below -

I (amperes)	0.5	1.0	2.0	3.0	4.0
V (volts)	1.6	3.4	6.7	10.2	13.2

Plot a graph between V and I and calculate the resistance of that resistor.

Explain the following.

1. Why is the tungsten used almost exclusively for filament of electric lamps?
2. Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal?
3. Why is the series arrangement not used for domestic circuits?
4. How does the resistance of a wire vary with its area of cross-section?
5. Why are copper and aluminium wires usually employed for electricity transmission?

Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?

If all the waste we generate is biodegradable, will this have no impact on the environment?

What are the problems caused by the non biodegradable wastes that we generate?

An electric heater of resistance 8 Ω draws 15 A from the service mains 2 hours. Calculate the rate at which heat is developed in the heater.

Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?

Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V?

Compare the power used in the 2 Ω resistor in each of the following circuits:

1. a 6 V battery in series with 1 Ω and 2 Ω resistors,
2. a 4 V battery in parallel with 12 Ω and 2 Ω resistors.

Why does the sky appear dark instead of blue to an astronaut?

Explain why the planets do not twinkle?

Why do stars twinkle?

What happens to the image distance in the eye when we increase the distance of an object from the eye?

Why is a normal eye not able to see clearly the objects placed closer than 25 cm?

Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is 25 cm.

How is the equal genetic contribution of male and female parents ensured in the progeny?