51.

The radius of nucleus of silver (atomic number = 47) is 3.4 x 10^-14 m. The electric potential on the surface of nucleus is (e = 1.6 x 10^-19 C)

• 1.99 x 10⁶ V

• 2.9 x 10⁶ V

• 4.99 × 10⁶ V

• 0.99 x 10⁶ V

In Young's experiment, the wavelength of red light is 7800 $\stackrel{\circ }{\mathrm{A}}$ and that of blue light is 5200 $\stackrel{\circ }{\mathrm{A}}$ . The value of n for which (n + 1)th blue band coincides with nth red band is

• 1

• 2

• 3

• 4

The energy band gap is maximum in

• metals

• superconductors

• insulators

• semiconductors

The phenomenon of polarization of light indicates that

• light is a longitudinal waves

• light is transverse wave

• light if not a wave

• light travels with the velocity of 3x 10⁸ m/s

Two lenses have powers equal to +2 D and -4 D respectively, the power of combination will be

• -2D

• +2D

• -4D

• +4D

In Young's double slit experiment one slit is covered with red filter and another slit is covered by green filter, then interference pattern will be

• red

• green

• yellow

• invisible

Which one of the following is used as a moderator in nuclear reaction?

• Uranium

• Heavy water

• Cadmium

• Plutonium

The rest mass of the photon is

• zero

• infinite

• between zero and infinite

• equal to that of electron

The K_{$\mathrm{\alpha }$} line from molybdenum (atomic number = 42) has a wavelength of 0.7078 $\stackrel{\circ }{\mathrm{A}}$. The wavelength of K_{$\mathrm{\alpha }$} line of zinc (atomic number = 30) will be

• 1 $\stackrel{\circ }{\mathrm{A}}$

• 1.3872 $\stackrel{\circ }{\mathrm{A}}$

• 0.3541 $\stackrel{\circ }{\mathrm{A}}$

• 0.5 $\stackrel{\circ }{\mathrm{A}}$

Decay constant of radioactive element is 1.5 × 10^-9/s. Average age of element is

• 1.5 × 10⁹

• 4.62 × 10⁸

• 6.67 × 10⁸

• 10.35 × 10⁸