1. Ball bearings are used in bicycles, cars, etc., because
the actual area of contact between the wheel and axle is increased
the effective area of contact between the wheel and axle is increased
the effective area of contact between the wheel and axle is reduced
None of the above statements is correct
2. Consider the following phenomena: 1. Size of the sun at dusk. 2. Colour of the sun at dawn 3. Moon being visible at dawn 4. Twinkle of stars in the sky 5. Polestar being visible in the sky
Which of the above are optical illusions?
1, 2 and 3
3, 4 and 5
1, 2 and 4
2, 3 and 5
3. Rainbow is produced when sunlight falls on drops of rain. Which of the following physical phenomena are responsible for this? 1. Dispersion
2. Refraction 3. Internal reflection
Select the correct answer using the codes below.
1 and 2 only
2 and 3 only
1 and 3 only
4. During a thunderstorm, the thunder in the skies is produced by the 1. meeting of cumulonimbus clouds in the sky 2. lightning that separates the nimbus clouds 3. violent upward movement of air and water particles
Select the correct answer using the codes given below.
1 only
2 and 3
1 and 3
None of the above produces the thunder
5. The known forces of nature can be divided into four classes, viz., gravity, electromagnetism, weak nuclear force and strong nuclear force. With reference to them, which one of the following statements is not correct?
Gravity is the strongest of the four
Electromagnetism acts only on particles with an electric charge
Weak nuclear force causes radioactivity
Strong nuclear force holds protons and neutrons inside the nucleus of an atom