If two soap bubbles of different radii are connected by a tube, then

• air flows from bigger bubble to the smaller bubble till sizes become equal

• air flows from bigger bubble to the smaller bubble till sizes are interchanged

• air flows from smaller bubble to bigger

• there is no flow of air

The thermo emf of a hypothetical thermocouple varies with the temperature θ of hot junction as  E = $\mathrm{a} \mathrm{\theta } + \mathrm{b} {\mathrm{\theta }}^2$ in volts, where the ratio $\frac{\mathrm{a}}{\mathrm{b}}$ is 700^o C. If the cold junction is kept at 0^o C, then the neutral temperature is

• 700^o C 

• 1400^o C

• 390^o C

• no neutral temperature is possible for this thermocouple

If the ratio of lengths, radii and Young's modulus of steel and brass wires shown in the figure are a, b Brass and c respectively, the ratio between the increase in lengths of brass and steel wires would

A soap bubble of radius r is blown up to form a bubble of radius 2r under isothermal conditions. If  T  is the surface tension of soap solution, the energy spent in the blowing

• $3 {\mathrm{\pi Tr}}^2$

• $6{\mathrm{\pi Tr}}^2$

• $12{\mathrm{\pi Tr}}^2$

• $24 {\mathrm{\pi Tr}}^2$

A current of 1.6 A is passed through a solution of CuSO_4. How many Cu⁺⁺ ions are liberated in one minute? (Electronic charge= 1.6 x 19^-19 C)

• 3 × 10²⁰

• 3 × 10¹⁰ 

• 6 × 10²⁰

• 6 × 10¹⁰

The sound waves after being converted into electrical waves are not transmitted as such because

• they travel with the speed of sound

• the frequency is not constant

• they are heavily absorbed by the atmosphere

• the height of antenna has to be increased several times

An engine moving towards a wall with a velocity 50 m/s  emits a note of 1.2 kHz. Speed of sound in air is 350 m/s. The frequency of the note after reflection from the wall as heard by the driver of the engine is

• 2.4 kHz

• 0.24 kHz

• 1.6 KHz

• 1.2 kHz

The surface temperature of the sun which has maximum energy emission at 500 nm is 6000 K. The temperature of a star which has maximum energy emission at 400 nm will be

• 8500 K

• 4500 K

• 7500 k

• 6500 K

29.

0.1 m² of water at 80°C is mixed with 0.3 m³ of water at 60°C. The final temperature of the mixture is

• 65^o C

• 70^o C

• 60^o C

• 75^o C

y = 3 sin $\mathrm{\pi } \left(\frac{\mathrm{t}}{2} - \frac{\mathrm{x}}{4}\right)$ represents an equation of a progressive wave, where t is in second and x is in metre. The distance travelled by the wave in 5 s is

• 8 m

• 10 m

• 5 m

• 32 m