61.

Light of wavelength 5000 $\stackrel{\circ }{\mathrm{A}}$ is incident normally on a slit of width 2.5 x 10^-4 cm. The angular position of second minimum from the central maximum is

• ${\sin }^{-1} \left(\frac{1}{5}\right)$

• ${\sin }^{-1} \left(\frac{2}{5}\right)$

• $\left(\frac{\mathrm{\pi }}{3}\right)$

• $\left(\frac{\mathrm{\pi }}{6}\right)$

An electron of mass m_e and a proton of mass m_p are accelerated through the same potential. Then, the ratio of their de-Broglie wavelengths is

• 1

• $\sqrt{\frac{{\mathrm{m}}_{\mathrm{e}}}{{\mathrm{m}}_{\mathrm{p}}}}$

• $\sqrt{\frac{{\mathrm{m}}_{\mathrm{p}}}{{\mathrm{m}}_{\mathrm{e}}}}$

• $\frac{{\mathrm{m}}_{\mathrm{p}}}{{\mathrm{m}}_{\mathrm{e}}}$

The half-life of a radioactive substance is 20 min. The time  taken between 50 % decay and 87.5 % decay of the substance will be

• 20 min

• 30 min

• 40 min

• 25 min

The ratio of the surface area of the nuclei ₅₂Te¹²⁵ to that of ₁₃Al¹²⁷ is 

• $\frac{5}{3}$

• $\frac{125}{17}$

• $\frac{1}{4}$

• $\frac{25}{9}$

If the frequency of incident light falling on a photosensitive metal is doubled, the kinetic energy of the emitted photoelectron is

• unchanged

• halved

• doubled

• more than twice its initial value

The significant result deduced from the Rutherford's scattering experiment is that

• whole of the positive charge is concentrated at the centre of atom

• there are neutrons inside the nucleus

• α-particles are helium nuclei

• electrons are embedded in the atom

On an average, the number of neutrons and the energy of a neutron released per fission of a uranium atom are respectively

• 2.5 and 2 keV

• 3 and 1 keV

• 2.5 and 2 MeV

• 2 and 2 keV

The inputs A, B and C to be given in order to get an output Y = 1 from the following circuit are

• 0, 1, 0

• 1, 0, 0

• 1, 0, 1

• 1, 1, 0

The collector resistance and the input resistance of a CE amplifier are respectively 10 kΩ and 2 kΩ. If β of the transistor is 49, the voltage gain of the amplifier is

• 125

• 150

• 245

• 200

The light emitting diode (LED) is

• a heavily doped p-n junction with no external bias

• a heavily doped p-n junction with reverse bias

• a heavily doped p-n junction with forward bias

• a lightly doped p-n junction with no external bias