(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.
(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 ?
For Balmer Series :
ni = 3
nf = 2