At which of the following temperature, the value of the surface tension of water is minimum?

• 4°C

• 25°C

• 50°C

• 75°C

In an isochoric process:

• ΔV = 0

• Δw = 0

• Δa = 0

• ΔT = 0

If the temperature difference on the two sides of a wall increases from 100°C to 200°C, its thermal conductivity :

• remains unchanged

• is doubled

• is halved

• becomes four times

14.

Let there be four articles having colours blue, red, black and white. When they are heated together and allowed to cool, which article will cool at the earliest?

• Blue

• Red

• Black

• White

An ideal gas is taken through the cycle A ➔ B ➔ C ➔ A, as shown in the figure. If the net heat supplied to the gas in the cycle is 5J, the work done by the gas in the process. C ➔ A is :

• -5 J

• -10 J

• -15 J

• -20 J

A piece of red glass when heated in dark to the red hot state will appear to be :

• White

• Red

• Green

• Invisible

A particle executing simple harmonic motion has a time period of 4 sec. After how much interval of time from t = 0 will its displacement be half of its amplitude :

• 1/3 sec

• 1/2 sec

• 2/3 sec

• 1/6 sec

A train approaches a stationary observer, the velocity of the train being 1/20 of the velocity of sound. A sharp blast is blown with the whistle of the engine at equal intervals of a second. The interval between the successive blasts as heard by the observer?

• 1/20 sec

• 1/20 min

• 19/20 sec

• 19/20 min

Which of the following equations represents a wave travelling along y-axis?

• y = A sin (x - ωt)

• x = A sin(ky - ωt)

• y = A sin(ky) cosωt

• y = A cos(ky)sinωt

In an adiabatic process, the state of a gas is changed from P₁, V₁, T₁ to P₂, V₂, T₂. Which of the following relation is correct?

• ${\mathrm{T}}_1{\mathrm{V}}_1^{\mathrm{\gamma }-1} ={\mathrm{T}}_2{\mathrm{V}}_2^{\mathrm{\gamma }-1}$

• ${\mathrm{P}}_1{\mathrm{V}}_1^{\mathrm{\gamma }-1} = {\mathrm{P}}_2{\mathrm{V}}_2^{\mathrm{\gamma }-1}$

• ${\mathrm{T}}_1{\mathrm{P}}_1^{\mathrm{\gamma }} = {\mathrm{T}}_2{\mathrm{P}}_2^{\mathrm{\gamma }}$

• ${\mathrm{T}}_1{\mathrm{V}}_1^{\mathrm{\gamma }} = {\mathrm{T}}_2{\mathrm{V}}_2^{\mathrm{\gamma }}$