31.

The ratio of the dimensions of Planck's constant and that of the moment of inertia is the dimension of

• frequency

• velocity

• angular momentum

• time

A photosensitive metallic surface has work function, h v_o, If photons of energy 2hv_o, fall on this surface, the electrons come out with a maximum velocity of 4 x 10⁶ m/s. When the photon energy is increased to 5 hv,, then maximum velocity of photoelectrons will be

• 2 × 10⁶ m/s

• 2 × 10⁷ m/s

• 8 × 10⁵ m/s

• 8 × 10⁶ m/s

Fission of nuclei is possible because the binding energy per nucleon in them

• increases with mass number at high mass numbers

• decreases with mass number at high mass numbers

• increases with mass number at low mass numbers 

• decreases with mass number at low mass numbers

In any fission process the ratio $\underset{\mathrm{Mass} \mathrm{of} \mathrm{parent} \mathrm{nucleus}}{\overset{\mathrm{Mass} \mathrm{of} \mathrm{fission} \mathrm{products}}{\to }}$ is

• less than 1

• greater than 1

• greater than 1

• depends on the mass of parent nucleus

Zener diode is used for

• producing oscillations in an oscillator

• amplification

• stabilisation

• rectification

The angular resolution of a 10 cm diameter telescope at a wavelength of 5000 A is of the order of

• 10⁶ rad

• 10^-2 rad

• 10^-4 rad

• 10^-6 rad

Carbon, silicon and germanium atoms have four valence electrons each. Their valence and conduction bands are separated by energy band gaps represented by _{${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}} , {\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Si}} \mathrm{and} {\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Ge}}$} respectively. Which one of the following relationships is true in their case?

• ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}} > {\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{si}}$

• ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}} = {\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Si}}$

• ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}} < {\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Ge}}$

• ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}} > {\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Si}}$

Choose the only false statement from the following

• Substances with energy gap ofthe order of 10 eV are insulators 

• The conductivity of a semiconductor increases with  increases in temperature

• In conductors the valence and conduction bands may overlap

• The resistivity of a semiconductor increases with increase in temperature

Copper has face-centred cubic ( FCC ) lattice with interatomic spacing equal to 2.54 A. The value of lattice constant for this lattice is

• 1.27 A^o

• 5.08 A^o

• 2.54 A^o

• 3.59 A^o

The total energy of an electron in the first excited state of hydrogen is about -3.4 eV. Its kinetic energy in this state is

• -3.4 eV

• -6.8 eV

• 6.8 eV

• 3.4 eV