IAS 2013 — Physics

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?

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 given below.

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?

Ball bearings are used in bicycles, cars, etc., because