A pan filled with hot food cools from 94°C to 86°C in 2 min. When the room temperature is 20°C. Howl ong will it cool from 74°C to 66°C ?

• 2 min

• 2.8 min

• 2.5 min

• 1.8 min

Four rods of same material with different radii r and length l are used to connect two heat reservoirs at different temperature. Which one will conduct most heat ?

• r = 1 cm, l = 1 m

• r = 1 cm, l = $\frac{1}{2} \mathrm{m}$

• r = 2 cm, l = 2 m

• r = 2 cm, l = $\frac{1}{2} \mathrm{m}$

A Carnot engine working between 300 K and 400 K has 800 J of useful work. The amount of heat energy supplied to the engine from the source is

• 2400 J

• 3200 J

• 1200 J

• 3600 J

A particle executing SHM has a maximum speed of 0.5 ms^-1 and maximum acceleration of 1.0 ms^-2. The angular frequency of oscillation is

• 2 rad s^-1

• 0.5 rad s^-1

• $2\mathrm{\pi } \mathrm{rad} {\mathrm{s}}^{-1}$

• $0.5 \mathrm{\pi } \mathrm{rad} {\mathrm{s}}^{-1}$

A source of sound is moving with a velocity of 50 ms^-1 towards a stationary observer. The observer measures the frequency of sound as 500 Hz. The apparent frequency of sound as heard by the observer when source is moving away from him with the same speed is (Speed of sound at room temperature is 350 ms^-1)

• 400 Hz

• 666 Hz

• 375 Hz

• 177.5 Hz

If there are only one type of charge in the universe, then (E → Electric field , dS → Area vector)

• $\oint \mathrm{E} \mathrm{dS} \ne 0$ on any surface

• $\oint \mathrm{E} \mathrm{dS} \mathrm{could} \mathrm{not} \mathrm{be} \mathrm{defined}$

• $\oint \mathrm{E} \mathrm{dS} = \infty$if charge is inside

• $\oint \mathrm{E} \mathrm{dS} = 0$ if charge is outside, = $\frac{\mathrm{q}}{{\mathrm{\epsilon }}_0}$ if charge is inside

17.

An electron of mass m, charge e falls through a distance h metre in a uniform electric field E. Then, time of fall

• $\mathrm{t} = \sqrt{\frac{2\mathrm{hm}}{\mathrm{eE}}}$

• $\mathrm{t} = \frac{2\mathrm{hm}}{\mathrm{eE}}$

• $\mathrm{t} = \sqrt{\frac{2\mathrm{eE}}{\mathrm{hm}}}$

• $\mathrm{t} = \frac{2\mathrm{eE}}{\mathrm{hm}}$

If E_ax and E_eq represents electric field at a point on the axial and equatorial line of a dipole. If points are at a distance r from the centre of the dipole, for r >> a

• E_ax = E_eq

• E_ax = − E_eq

• E_ax = − 2 E_eq

• E_eq = 2 E_ax

Nature of equipotential surface for a point charge is

• Ellipsoid with charge at foci

• Sphere with charge at the centre of the sphere

• Sphere with charge on the surface of the sphere

• Plane with charge on the surface

A particle of mass 1 g and charge 1 µC is held at rest on a frictionless horizontal surface at distance 1 m from the fixed charge 2 mC. If the particle is released, it will be repelled. The speed of the particle when it is at a distance of 10 m from the fixed charge.

• 60 ms^-1

• 100 ms^-1

• 90 ms^-1

• 180 ms^-1