White light is used to illuminate two slits in Young's double slit experiment. The separation between the slits is b and the screen is at a distance d (>>b) from the slits. At a point on the screen directly in front of one of the slits, which wavelengths are missing?

• $\frac{\mathrm{b}}{\mathrm{d}}, \frac{\mathrm{b}}{3\mathrm{d}}, \frac{\mathrm{b}}{5\mathrm{d}}$

• $\frac{{\mathrm{b}}^2}{2\mathrm{d}}, \frac{{\mathrm{b}}^2}{3\mathrm{d}}, \frac{{\mathrm{b}}^2}{6\mathrm{d}}$

• $\frac{{\mathrm{b}}^2}{\mathrm{d}}, \frac{{\mathrm{b}}^2}{3\mathrm{d}}, \frac{{\mathrm{b}}^2}{5\mathrm{d}}$

• $\frac{\mathrm{b}}{2\mathrm{d}}, \frac{\mathrm{b}}{3\mathrm{d}}, \frac{\mathrm{b}}{6\mathrm{d}}$

The wavelength λ of  a photon and the de-Broglie wavelength of an electron have the same value. Find the ratio of the energy of a photon to the kinetic energy of an electron in terms of mass m, the speed of light c and Planck constant.

• $\frac{\mathrm{\lambda mc}}{\mathrm{h}}$

• $\frac{\mathrm{hmc}}{\mathrm{\lambda }}$

• $\frac{2\mathrm{hmc}}{\mathrm{\lambda }}$

• $\frac{2\mathrm{\lambda mc}}{\mathrm{h}}$

A beam of light composed of red and green rays is incident obliquely at a point on the face of a rectangular glass slab. When coming out on the opposite parallel face, the red and green rays emerge from.

• Two points propagating in two different non- parallel directions.

• Two points propagating in two different parallel directions

• one point propagating in two different directions.

• one point propagating in the same direction.

An isotropic point source of light is suspended h metre vertically above the centre of the circular table of radius r metre. Then, the ratio of illumenances at the centre to that at the edge of the table is

• $1 + \left(\frac{{\mathrm{r}}^2}{{\mathrm{h}}^2}\right)$

• $1 + \left(\frac{{\mathrm{h}}^2}{{\mathrm{r}}^2}\right)$

• ${\left\{1 + \frac{{\mathrm{r}}^2}{{\mathrm{h}}^2}\right\}}^{3/2}$

• ${\left\{1 + \frac{{\mathrm{h}}^2}{{\mathrm{r}}^2}\right\}}^{3/2}$

A photocell is illuminated by a small bright source placed 1m away. When the same source of light is placed 2m away, the electrons emitted by photo cathode

• Carry one quarter of their previous energy

• carry one quarter of their previous momenta

• are half as numerous

• are one quarter as numerous

A light of wavelength 2000 A^o falls on a metallic surface of work function 5.01 eV then required potential difference to slope fastest photoelectron is (h = 6.62 x 10^-34J-s)

• 4.8V

• 3.6V

• 2.4V

• 1.2V

The enregy of a photon corresponding to the visible light maximum wavelength is nearly

• 7ev

• 3.2eV

• 1eV

• 1.6eV

The energy in MeV is released due to transformation of 1kg mass completely into energy is (c=3×10⁸ m/s)

• 7.625×10MeV

• 10.5×10²⁹MeV

• 2.8×10^-28MeV

• 5.625×10²⁹MeV

20 kV potential is applied across X-ray tube, the minimum wavelength of X-ray emitted will be

• 0.62 A^o

• 0.37 A^o

• 1.62 A^o

• 1.31 A^o

If work function of a metal is 4.2 eV, the cut off wavelength is

• 8000 A^o

• 7000 A^o

• 1472 A^o

• 2950 A^o