31.

A engine pumps up 100 kg of water through a height of 10 m in 5s. Given that, the efficiency of engine is 60%. If g = 10 ms^-2, the power of this engine is

• 3.3 kW

• 0.33 kW

• 0.033 kW

• 33 kW

If the electric flux entering and leaving an enclosed surface respectively are ${\mathrm{\varphi }}_1 \mathrm{and} {\mathrm{\varphi }}_2$ , the electric charge inside the surface will be

• $\frac{{\mathrm{\varphi }}_2 - {\mathrm{\varphi }}_1}{{\mathrm{\epsilon }}_{\mathrm{o}}}$

• $\frac{{\mathrm{\varphi }}_2 + {\mathrm{\varphi }}_1}{{\mathrm{\epsilon }}_{\mathrm{o}}}$

• $\frac{{\mathrm{\varphi }}_1 - {\mathrm{\varphi }}_2}{{\mathrm{\epsilon }}_0}$

• ${\mathrm{\epsilon }}_0 \left({\mathrm{\varphi }}_1 + {\mathrm{\varphi }}_2 \right)$

If the sun rays are incidenting at 60° angle and intensity is I. If the sun rays are made incident at 30° angle, then what will be the intensity?

• $\frac{\mathrm{I}}{\sqrt{3}}$

• $\sqrt{3} \mathrm{l}$

• 3 l

• $\frac{\mathrm{l}}{3}$

The reason of current flow in p-n junction in forward bias is

• drifting of charge carriers

• drifting of minority charge carriers

• diffussion of charge carriers

• All of the above

Relation between wavelength of photon and electron of same energy is

• λ_ph > λ_e

• λ_ph < λ_e

• λ_ph = λ_e

• $\frac{{\mathrm{\lambda }}_{\mathrm{e}}}{{\mathrm{\lambda }}_{\mathrm{ph}}}$= constant

If prism angle α = 1^o , μ= 1.54, distance between screen and prism (D) = 0. 7 m, distance between prism and source $\mathrm{\alpha } = 0.3 \mathrm{m} , \mathrm{\lambda } = 180 \mathrm{\pi }$ nm, then in Fresnal biprism find the value of β (fringe width).

• 10^-4 m

• 10^-3 mm

• 10^-4 × $\mathrm{\pi }$m

• $\mathrm{\pi } \times {10}^{-3 }\mathrm{m}$

According to Bohr's model of hydrogen atom, relation between principal quantum number n and radius of stable orbit is

• r ∝ $\frac{1}{\mathrm{n}}$

• r ∝ n

• r ∝ $\frac{1}{{\mathrm{n}}^2}$

• r ∝ n²

Work function of a metal is 5.2 x 10^-18, then its threshold wavelength will be

• 736.7 A^o

• 760.7 A^o

• 301 A^o

• 344.4 A^o

Remaining quantity (in%) of radioactive element after 5 half lives is

• 4.125%

• 3.125%

• 31.1%

• 42.125%

To get three images of a single object, we should have two plane mirrors at an angle of

• 60^o

• 90^o

• 120^o

• 30^o