The rms speed of the molecules of a gas in a vessel is 400 ms. If half of the gas leaks out, at constant temperature, the rms speed of the remaining molecules will be

• 800 ms^-1

• $400\sqrt{2} {\mathrm{ms}}^{-1}$

• 400 ms^-1

• 200 ms^-1

An electron tube was sealed off during manufacture at a pressure of 1.2 x 10^-7 mm of mercury at 27°C. Its volume is 100 cm³. The number of molecules that remain in the tube is

• 2 × 10¹⁶

• 3 × 10¹⁵

• 3.86 × 10¹¹

• 5 × 10¹¹

A liquid wets a solid completely. The meniscus of the liquid in a sufficiently long tube is

• flat

• concave

• convex

• cylindrical

A steel scale is to be prepared such that the millimetre intervals are to be accurate within 6 x 10^-5 mm. The maximum temperature variation during the ruling of the millimetre marks is (α = 12 x 10^-6/° C) 

• 4.0° C

• 4.5° C

• 5.0° C

• 3° C

A constant volume gas thermometer works on

• Archimede's principle

• Pascal's law

• Boyle's law

• Charle's law

The equation of a simple harmonic motion is X = 0.34 cos (3000 t + 0.74), where X and t are in mm and sec respectively. The frequency of the motion in Hz is

• 3000

• $\frac{3000}{2\mathrm{\pi }}$

• $\frac{0.74}{2\mathrm{\pi }}$

• $\frac{3000}{\mathrm{\pi }}$

The unit of specific conductivity is

• Ω cm^-1

• Ω cm^-2

• Ω^-1 cm^-1

• Ω cm^-3

38.

If 96500 C of electricity liberates 1 g equivalent of any substance, the time taken for a current of 0.15A to deposit 20 mg of copper from a solution of copper sulphate is (chemical equivalent of copper = 32)

• 5 min 20 s

• 6 min 42 s

• 4 min 40 s

• 5 min 50 s

An electric motor operates on a 50 V supply and a current of 12 A. If the efficiency of the motor, is 30%, what is the resistance of the winding of the motor

• 6 Ω

• 4 Ω

• 2.9 Ω

• 3.1 Ω

Two long straight wires are set parallel to each other. Each carries a current in the same direction and the separation between them is 2 r. The intensity of the magnetic field mid-way between them is

• $\frac{{\mathrm{\mu }}_0\mathrm{i}}{\mathrm{r}}$

• $\frac{4{\mathrm{\mu }}_0\mathrm{i}}{\mathrm{r}}$

• Zero

• $\frac{{\mathrm{\mu }}_0\mathrm{i}}{4\mathrm{r}}$