Education

 CBSE notes-Light What is the nature, size and position of the image formed of an object at infinity? Explain how it is used as a doctor’s mirror. When an object is placed at infinity from a concave mirror, the image formed is (i) real and inverted (ii) highly diminished and (iii) at the focus When the object is at infinity, the image is formed at the focus of the concave mirror, hence the mirror can concentrate all the parallel rays of the light to its focus. This explains the use of concave mirror as a doctor’s head-mirror. A concave mirror is used as a head-mirror by the doctors to concentrate light on the body parts to be examined.

CBSE notes-Light Explain why the planets do not twinkle? Planets do not twinkle because they appear larger in size than the stars as they are relatively closer to earth. Planets can be considered as a collection of a large number of point-size sources of light. The different parts of these planets produce either brighter or dimmer effect in such a way that the average of brighter and dimmer effect is zero. Hence, the twinkling effects of the planets are nullified and they do not twinkle.