31.

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 neutron number changes

If in a p-n junction diode, a square input signal of 10V is applied as shown Then the output signal across RL will be 

A photon of frequency v has a momentum associated with it. If c is the velocity of light, the momentum is

• v /c

• h v c

• h v /c²

• h v /c²

For the given uniform square lamina ABCD, whose centre is O,

• 

• I_AD = 3I_EF

• I_AC = I_EF

• I_AC = I_EF

The half-life period of a radio-active element X is same as the mean life-time of another radio-active element Y. Initially, they have the same number of atoms. Then

• X will decay faster than Y

• Y will decay faster than X

• X and Y have same decay rate initially

• X and Y have same decay rate initially

Carbon, silicon and germanium have four valence electrons each. At room temperature which one of the following statements is most appropriate?

• The number of free conduction electrons is significant in C but small in Si and Ge

• The number of free conduction electrons is negligibly small in all the three

• The number of free electrons for conduction is significant in all the three

• The number of free electrons for conduction is significant in all the three

Which of the following transitions in hydrogen atoms emit photons of highest frequency?

• n = 2 to n = 6

• n = 6 to n = 2

• n = 2 to n =1

• n = 2 to n =1

Two lenses of power -15D and +5D are in contact with each other. The focal length of the combination is

• -20 cm

• -10 cm

• +20 cm

• +20 cm

A sound absorber attenuates the sound level by 20 dB. The intensity decreases by a factor of

• 1000

• 10000

• 10

• 10

Young’s double slit experiment the intensity at a point where the path-difference is λ/6(λ being the wavelength of the light used) is I. If I₀ denotes the maximum intensity, I/I₀ is equal to

• 
• 

• 1/2

• 1/2