31.

The specific charge of a proton is 9.6 x 10⁷ C/kg. The specific charge of an alpha particle will be

• 9.6 x10⁷ C/kg

• 19.2 x 10⁷ C/kg

• 4.8 x10⁷ C/kg

• 2.4 x 10⁷ C/kg

If λ₁ and λ₂ are the wavelengths of the first members of the Lyman and Paschen series respectively, then λ₁ : λ₂ is

• 1:3

• 1: 30

• 7: 50

• 7: 108

Activity of a radioactive sample decreases to (1/3)rd of its original value in 3 days. Then, in 9 days its activity will become

• (1/27) of the original value

• (1/9) of the original value

• (1/18) of the original value

• (1/3) of the original value

If r₁ and r₂ are the radii of the atomic nuclei of mass numbers 64 and 125 respectively, then the ratio ( r₁/ r₂ ) is

• $\frac{64}{125}$

• $\sqrt{\frac{64}{125}}$

• $\frac{5}{4}$

• $\frac{4}{5}$

the ionization energy of Li²⁺ is equal to 

• 9hcR

• 6hcR

• 2hcR

• hcR

The principle of LASER action involves

• amplification of particular frequency emitted by the system

• population inversion

• stimulated emission

• All of the above

Which of the following is unipolar transistor?

• p-n-p transistor

• n-p-n transistor

• Field effect transistor

• Point contact transistor

Light of frequency v falls on material of threshold frequency v_o, Maximum kinetic energy of emitted electron is proportional to 

• ν - ν_o

• ν

• $\sqrt{\mathrm{v} - {\mathrm{v}}_{\mathrm{o}}}$

• v_o

A light movs from denser to rarer medium, which of the following is correct?

• Energy increases

• Frequency increases

• Phase changes by 90°

• Velocity increases

For a given lens, the magnification was found to be
twice as large as when the object was 0.15 m
distant from it as when the distance was 0.2 m. The
focal length of the lens is

• 1.5 m

• 0.20 m

• 0.10 m

• 0.05 m