An astronomical telescope consists of two convex lenses having focal length 80 cm and 4 cm. When it is in normal adjustment, what is its:
(i) Length,
(ii) Magnifying power?
(i) Define ‘unified atomic mass unit’.
(ii) Find the minimum energy which a gamma ray photon should possess so that it is capable of producing an electron — positron pair.
(i)
Unified atomic mass unit - United atomic mass unit is equal to one-twelfth of the mass of carbon - 12 atom. It is denoted by U.
1u =1.0003179 amu (Physical scale).
= 1.0000043 amu (Chemical scale).
(ii)
The minimum energy for a gamma-ray photon to produce electron-positron pair is twice the rest mass of electron. It is 1.022 meV.