The figure shows a P-V diagram. How does the work done in the process change with time?

• First decreases and then increases

• First increases and then decreases

• Continuously decreases

• Continuously increases

A siren emitting sound of frequency 800 Hz is going away from a static listener with a speed of 30 m/s. Frequency of sound to be heard by the listener is (velocity of sound = 330 m/s).

• 286.5 Hz

• 481.2 Hz

• 733.3 Hz

• 644.8 Hz

A wire fixed at the upper end stretches by length $\mathrm{\Delta l}$ by applying a force F. The work done in stretching is

• $\frac{\mathrm{F}}{2\mathrm{\Delta l}}$

• FΔl

• 2 FΔl

• $\frac{\mathrm{F\Delta l}}{2}$

The Young's modulus of a wire is numerically equal to the stress which will

• not change the length of the wire

• double the length of the wire

• increase the length

• change the radius of the wire to half

The musical interval between two tones of frequency 400 Hz and 200 Hz is

• 2

• 200

• 1

• 0.5

According to Newton's law of cooling, the rate of cooling of a body is proportional to ($\mathrm{\Delta \theta }$)ⁿ 1, where Δθ is the difference of the temperature of the body and the surroundings and n is equal to

• 2

• 3

• 4

• 1

Which of the following parameters does not characterize the thermodynamic state of matter?

• Volume

• Temperature

• Pressure

• Work

28.

Point charges + 4q, - q and+ 4q are kept on the x-axis at points x = 0, x = a and x = 2a respectively, then

• only- q is in stable equilibrium

• all the charges are in stable equilibrium

• all the charges are in unstable equilibrium

• none of the above

If E_a be the electric field strength of a short dipole at a point on its axial line and E_e that on equilateral line at the same distance, then

• E_e = 2E_a

• E_a = 2E_e

• E_a = E_e

• none of these

If emf E = 4 cos 1000t volt is applied to an L-R circuit of inductance 3 mH and resistance 4 Ω, the amplitude of the current in the circuit is

• $\frac{4}{\sqrt{7}}\mathrm{A}$

• 1.0 A

• $\frac{4}{7}\mathrm{A}$

• 0.8 A