The threshold frequency for a metallic surface corresponds to an energy of 6.2 eV, and the stopping potential for a radiation incident on this surface 5 V. The incident radiation lies in

• X-ray region

• ultra-violet region

• infra-red region

• visible region

B.

ultra-violet region

Who discovered X-rays?

• Roentgen

• Madam Curie

• Rutherford

•  All of these

If  ${\mathrm{\lambda }}_{\mathrm{\nu }}, {\mathrm{\lambda }}_{\mathrm{x}} \mathrm{and} {\mathrm{\lambda }}_{\mathrm{m}}$represent the wavelengths of visible light, X-rays and microwaves respectively, then

• ${\mathrm{\lambda }}_{ \mathrm{m}} > {\mathrm{\lambda }}_{ \mathrm{x}} > {\mathrm{\lambda }}_{ \mathrm{\nu }}$

• ${\mathrm{\lambda }}_{\mathrm{v}} >{\mathrm{\lambda }}_{\mathrm{m}} > {\mathrm{\lambda }}_{\mathrm{x}}$

• ${\mathrm{\lambda }}_{\mathrm{m}}> {\mathrm{\lambda }}_{\mathrm{v}} > {\mathrm{\lambda }}_{\mathrm{x}}$

• ${\mathrm{\lambda }}_{\mathrm{v}} > {\mathrm{\lambda }}_{\mathrm{x}} > {\mathrm{\lambda }}_{\mathrm{m}}$

In gamma ray emission from a nucleus

• both the neutron number and the proton number change

• there is no change in the proton number and the neutron number

• only the neutron number changes

• only the proton number changes