Carnot engine having an efficiency of 1/10 as heat engine, is used as a refrigerator. If the work done on the system is 10 J, the amount of energy absorbed from the reservoir at lower temperature is

• 1 J

• 90 J

• 99 J

• 99 J

The bulk modulus of a spherical object is ‘B’. If it is subjected to uniform pressure ‘p’, the fractional decrease in radius is

• p/B

• B/2p

• 3p/B

• 3p/B

A spherical black body with a radius of 12 cm radiates 450-watt power at 500 K. If the radius were halved and the temperature doubled, the power
radiated in watt would be

• 225

• 450

• 1800

• 1800

24.

Two blocks A and B of masses 3m and m respectively are connected by a massless and inextensible string. The whole system is suspended by a massless spring as shown in the figure. The magnitudes of acceleration of A and B immediately after the string is cut, are respectively

• g,g/3

• g/3, g

• g,g

• g,g

A rope is wound around a hollow cylinder of mass 3 kg and radius 40 cm. What is the angular acceleration of the cylinder if the rope is pulled with a force of 30 N?

• 25 m/s²

• 0.25 rad/s²

• 25 rad/s²

• 25 rad/s²

The two nearest harmonics of a tube closed at one end and open at other end are 220 Hz and 260 Hz. What is the fundamental frequency of the system?

• 10 Hz

• 20 Hz

• 30 Hz

• 30 Hz

A potentiometer is an accurate and versatile device to make electrical measurements of E.M.F, because the method involves :

• Cells

• Potential gradients

• A condition of no current flow through the galvanometer

• A condition of no current flow through the galvanometer

A 250-Turn rectangular coil of length 2.1 cm and width 1.25 cm carries a current of 85 μA and subjected to a magnetic field of strength 0.85 T. Work done for rotating the coil by 180° against the torque is

• 9.1 μJ

• 4.55 μJ

• 2.3 μJ

• 2.3 μJ

Figure shows a circuit contains three identical resistors with resistance R = 9.0 Ω each, two identical inductors with inductance L = 2.0 mH each, and an ideal battery with emf  ε= 18 V. The current'i' through the battery just after the switch closed is

• 2 mA

• 0 mA

• 2 A

• 2 A

A capacitor is charged by a battery. The battery is removed and another identical uncharged capacitor is connected in parallel. The total electrostatic energy of resulting system

• Increases by a factor of 4

• Decreases by a factor of 2

• Increases by a factor of 2

• Increases by a factor of 2