For photoelectric emission from certain metal, the cut-off frequency is v. If radiation of frequency is v. If radiation of frequency 2v impinges on the metal plate, the maximum possible velocity of the emitted electrons will be (m is the electron mass)

A certain mass of hydrogen is changed to helium the process of fusion. The mass defect in fusion reaction is 0.02866 u. The energy liberated per u is (given 1 u =931 MeV)

• 2.67 MeV

• 26.7 MeV

• 6.675 MeV

• 6.675 MeV

Ratio of longest wavelength corresponding to Lyman and Balmer series in hydrogen spectrum is 

• 5/27

• 3/23

• 7/29

• 7/29

44.

The half-life of radioactive isotope X is 20 yr. It decays to another element Y which is stable.The two elements X and Y were found to be in the ratio 1:& in a sample of given rock is estimated to be

• 40 yr

• 60 yr

• 80 yr

• 80 yr