(i) Draw a ray diagram to show how the image of a distant object is formed by a refracting astronomical telescope when in normal use.
(ii) State one advantage of a reflecting astronomical telescope over a refracting astronomical telescope.
Cause of Spherical Aberration:
The cause of spherical aberration is the spherical shape of the reflecting or the refracting surface due to which the focal length is different for different zones-greater the distance of the zone from the centre of the lens, smaller is its focal length.
Method to Reduce Spherical Aberration:
(i) By using stops.
(ii) By using crossed lens.
(iii) By proper orientation of lens.
(iv) By using two lenses.
(i) What is meant by the term activity of a radioactive substance.
(ii) A radioactive sample has a half life of 1.4 x 1016 seconds and a mass number of 238. Calculate the number of disintegration/s of 1g of this sample.
Which of the radiations, α-rays, β-rays, or γ-rays are :
(i) easily absorbed by matter ?
(ii) similar to X-rays ?