31.

When temperature of an ideal gas is increased from 27°C to 227°C, its rms speed is changed from 400 m/s to v_s Then, v_s is

• 516 m/s

• 450 m/s

• 310 m/s

• 746 m/s

A prism of refractive index $\sqrt{2}$ has a refracting angle of 60°. At what angle a ray must be incident on it so that it suffers a minimum deviation.

• 45⁰

• 60⁰

• 90⁰

• 180⁰

The radius of the convex surface of planoconvex lens is 20 cm and the refractive index of the material of the lens is 1.5. The focal length is

• 30cm

• 50 cm

• 30 cm

• 40 cm

If work function of a metal is 4.2 eV, the cut off wavelength is

• 8000 A^o

• 7000 A^o

• 1472 A^o

• 2950 A^o

The work function of sodium is 2.3 eV. The threshold wavelength of sodium will be

• 2900 A^o

• 2500 A^o

• 5380 A^o

• 1200 A^o

A short linear object of length b lies along the axis of a concave mirror of focal length ' f ' at a distance 'u' from the pole of the mirror, what is the size of image?

• $\left(\frac{\mathrm{f}}{\mathrm{u}-\mathrm{f}}\right) \mathrm{b}$

• ${\left(\frac{\mathrm{f}}{\mathrm{u}-\mathrm{f}}\right)}^2 \mathrm{b}$

• $\left(\frac{\mathrm{f}}{\mathrm{u}-\mathrm{f}}\right) {\mathrm{b}}^2$

• $\left(\frac{\mathrm{f}}{\mathrm{u}-\mathrm{f}}\right)$

The minimum wavelength of X-ray emitted by X-ray tube is 0.4125 A^o. The accelerating voltage is

• 30 kV

• 50 kV

• 80 kV

• 60 kV

The refractive index of the material of the prism and liquid are 1.56 and 1.32 respectively. What will be the value of 0 for the following refraction?

• $\sin \mathrm{\theta }\ge \frac{13}{11}$

• $\sin \mathrm{\theta } \ge \frac{11}{13}$

• $\sin \mathrm{\theta } \ge \frac{\sqrt{3}}{2}$

• $\sin \mathrm{\theta }\ge \frac{1}{\sqrt{2}}$

What should be the minimum value of refractive index of the material of the prism for the reflections to take place as shown in the figure? 

• 1.7

• 1.4

• 1.2

• 2.7

A person who can see things most clearly at a distance of 10 cm, requires spectacles to enable to see clearly things at a distance of 30 cm. What should be the focal length of the spectacles?

• 15 cm (Concave)

• 15 cm (convex)

• 10 cm

• 0