List of top Science Questions

Suggest three measures to protect ourselves from lightning.
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?
Describe the construction of a kaleidoscope.
A sound wave travels at a speed of 339 ms–1. If its wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?
Boojho stands at A just on the side of a plane mirror as shown in Fig. 
Boojho stands at A just on the side of a plane mirror
Can he see himself in the mirror? Also, can he see the image of objects situated at P, Q and R?
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?

Would the bulb glow after completing the circuit shown in Fig. 9.14 if instead of safety pin we use an eraser?

Would the bulb glow after completing the circuit

Give two differences between a zygote and a foetus.
Why do we apply paint on iron articles?
Describe with the help of a diagram an instrument which can be used to detect a charged body.
How do good animal husbandry practices benefit farmers?
In each of the following a force, F is acting on an object of mass, m. The direction of displacement is from west to east shown by the longer arrow. Observe the diagrams carefully and state whether the work done by the force is negative, positive or zero.
Observe work done by the force is negative, positive or zero
The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?
Explain why sliding friction is less than static friction.
Find out the position of the image of an object situated at A in the plane mirror

(a) Find out the position of the image of an object situated at A in the plane mirror.
(b) Can Paheli at B see this image?
(c) Can Boojho at C see this image?
(d) When Paheli moves from B to C, where does the image of A move?
Draw the structure of a neuron and explain its function.
In the following statements, tick ‘T’ against those which are true, and ‘F’ against those which are false.
  1. Sound cannot travel in vacuum. (T/F)
  2. The number of oscillations per second of a vibrating object is called its time period. (T/F)
  3. If the amplitude of vibration is large, sound is feeble. (T/F)
  4. For human ears, the audible range is 20 Hz to 20,000 Hz. (T/F)
  5. The lower the frequency of vibration, the higher is the pitch. (T/F)
  6. Unwanted or unpleasant sound is termed as music. (T/F)
  7. Noise pollution may cause partial hearing impairment. (T/F)
A stone of 1 kg is thrown with a velocity of 20 m s–1 across the frozen surface of a lake and comes to rest after traveling a distance of 50 m. What is the force of friction between the stone and the ice?
A battery of 9 V is connected in series with resistors of 0.2 Ω, 0.3 Ω, 0.4 Ω , 0.5 Ω and 12 Ω, respectively. How much current would flow through the 12 Ω resistor?
Find the energy in joules consumed in 10 hours by four devices of power 500 W each.
Explain why a charged body loses its charge if we touch it with our hand.

The bulb in the circuit shown in Fig. does not glow. Can you identify the problem? Make necessary changes in the circuit to make the bulb glow.

The bulb in the circuit

Balance the following chemical equations.
(a) HNO3 +Ca(OH)2 \(→\) Ca(NO3)2 + H2O 
(b) NaOH + H2SO4 \(→\) Na2SO4 + H2O 
(c) NaCl + AgNO3 \(→\) AgCl + NaNO3 
(d) BaCl + H2 SO4 \(→\) BaSO4 + HCl
Define asexual reproduction. Describe two methods of asexual reproduction in animals.
Sketch larynx and explain its function in your own words.