21.

During an isothermal expansion, a confined ideal gas does - 150 J of work against its surroundings. This implies that

• 300 J of heat has been added to the gas

• no heat is transferred because the process is isothermal

• 150 J of heat has been added to the gas

• 150 J of heat has been added to the gas

A parallel plate condenser has a uniform electric field E (V/m) in the space between the plates. If the distance between the plates is d(m) and area of each plate is A(m²) the energy (joule) stored in the condenser is

If power dissipated in the 9Ω resistor in the circuit shown is 36 W, the potential difference across the 2Ω resistor is

• 8 V

• 10 V 

• 2 V

• 2 V

A current 2 A flows through a 2 Ω resistor when connected across a battery. The same battery supplies a current of 0.5 A when connected across a 9 Ω resistor. The internal resistance of the battery is 

• 1/3 Ω

• 1/4 Ω

• 1 Ω

• 1 Ω

The electric and the magnetic field, associated with an electromagnetic wave, propagating along the +z - axis, can be represented by

A charge Q is enclosed by a Gaussian spherical surface of radius R. If the radius is doubled, then the outward electric flux will 

• be reduced to half

• remain the same

• be doubled

• be doubled

The rate of increase of thermo - emf with temperature at the neutral temperature of a thermocouple

• is zero

• depends upon the choice of the two materials of the thermocouple

• is negtive

• is negtive

There are four light -weight rod samples A, B, C D separately suspended by threads. A bar magnet is slowly brought near each sample and the following observations are noted

(i)  A is feebly repelled

(ii) B is feebly attracted

(iii) C is strongly attracted

(iv) D remains unaffected

• C is a diamagnetic material

• D is of a ferromagnetic material

• A is of a non- magnetic material

• A is of a non- magnetic material

In an AC circuit, an alternating voltage 100t volt is connected to a capacitor of capacity 1μF. The rms value of the current in the circuit is 

• 100 mA

• 200 mA

• 20 mA

• 20 mA

Four electric charge +q, +q, -q and -q  are placed at the corners of a square of side 2L (see figure). The electric potential at point A, mid-way between the two charges + q and +q, is

• 
• 

• zero

• zero