51.

The galvanometer resistance is 30 Ω and it is connected to 2 V battery along with a resistance 2000 Ω in series. A full scale deflection of 25 divisions is obtained. In order to reduce this deflection to 20 divisions, the resistance in series should be

• 2470 Ω

• 2370 Ω

• 2180 Ω

• 2210 Ω

A thin bar magnet of length 2 L is bent at the mid-point so that the angle between them is 60°. The new length of the magnet is

• L/2√3

• √3 L/2

• L

• 2 L/3

The magnetic flux through each turn of a coil having 200 turns is given as (t² $-$ 1) x 10^-3 Wb, where t is in second. The emf induced in the coil at t = 3s is

• 0.7 V

• 1.2 V

• 0.8 V

• 0.9 V

A vessel of depth t is half filled with a liquid having refractive index n₁ and the other half is filled with water of having refractive index n₂. The apparent depth of the vessel as viewed from top is

• $\frac{2\mathrm{t} \left({\mathrm{n}}_1 + {\mathrm{n}}_2\right)}{{\mathrm{n}}_1 {\mathrm{n}}_2}$

• $\frac{\mathrm{t} {\mathrm{n}}_1 {\mathrm{n}}_2}{\left({\mathrm{n}}_1 + {\mathrm{n}}_2\right)}$

• $\frac{\mathrm{t} \left({\mathrm{n}}_1 + {\mathrm{n}}_2\right)}{2 {\mathrm{n}}_1 {\mathrm{n}}_2}$

• $\frac{{\mathrm{n}}_1 {\mathrm{n}}_2}{\left( {\mathrm{n}}_1 + {\mathrm{n}}_2 \right)}$

In photoelectric effect, the number of photo-electrons emitted is proportional to

• velocity of incident beam

• frequency of incident beam

• intensity of incident beam

• work function for cathode material

A change of 8.0 mA in the emitter current brings a change of 7. 9 mA in the collector current. The value of a will be

• 0.96

• 0.93

• 0.90

• 0.99

The half-life of ¹⁹⁸Au is 2.7 days. The average life is

• 4 days

• 3.4 days

• 3.9 days

• None of the above

The de-Broglie wavelength of electron falling on the target in an X-ray tube is),. The cut-off wavelength of the emitted X-ray is

• ${\mathrm{\lambda }}_0 = \frac{{\left( \mathrm{m} \mathrm{c} \mathrm{\lambda } \right)}^2}{\mathrm{h}}$

• ${\mathrm{\lambda }}_0 = \frac{{\mathrm{m}}^2 \mathrm{c\lambda }}{{\mathrm{h}}^2}$

• ${\mathrm{\lambda }}_0 = \frac{2 \mathrm{mc} {\mathrm{\lambda }}^2}{\mathrm{h}}$

• ${\mathrm{\lambda }}_0 = \frac{\mathrm{m} \mathrm{c} {\mathrm{\lambda }}^2}{{\mathrm{h}}^2}$

If M_O is the mass of an oxygen isotope ₈O¹⁷ M_p and M_n are the masses of a proton and a neutron, respectively, the nuclear binding energy of the isotope is

• M_O c²

• ( M_O - 17M_n ) c²

• (M_O - 8M_p ) c²

• ( 8 M_p + 9 M_n - M_O)

A nucleus disintegrates into two nuclear parts which have their velocities in the ratio 2 : 1. The ratio of their nuclear size will be

• 2^1/3 : 1

• 1 : 3^1/2

• 3^1/2 : 1

• 1 : 2^1/2