31.

The equivalent resistance between A and B is

• 10 Ω

• 20 Ω

• 30 Ω

• 49 Ω

An electrical cable of copper has just one wire of radius 9 mm. Its resistance is 5Ω. The single wire of the cable is replaced by 6 different well-insulated copper wires each of radius 3 mm. The total resistance of the cable will now be equal to:

• 270 Ω

• 90 Ω

• 45 Ω

• 7.5 Ω

A current of 2 amperes flowing through a conductor produces 80 joules of heat in ten seconds. The resistance of the conductor is:

• 0.5 Ω

• 2 Ω

• 4 Ω

• 20 Ω

A thermoelectric refrigerator works on

• Joule effect

• Seebeck effect

• Peltier's effect

• Thermionic effect

A small circular flexible loop of wire of radius 'r' carries a current I. It is placed in a uniform magnetic field B. The tension in the loop will be doubled if :

• I is doubled

• B is halved

• r is doubled

• Both B and I are doubled

Two parallel wires carrying current in the same direction attract each other because of :

• the potential difference between them

• mutual inductance between them

• the electric force between them

• the magnetic force between them

A hydrogen atom is paramagnetic. A hydrogen molecule is

• diamagnetic

• paramagnetic

• ferromagnetic

• none of these

A galvanometer has a resistance of 400 Ω and deflects full scale for a current of 0.2 mA through it. The shunt resistance required to covert it into 3A ammeter is :

• 0.027 Ω

• 0.054 Ω

• 0.0135 Ω

• none of these

The power factor of a series LCR circuit when at resonance is :

• zero

• 0.5

• 1.0

• Depends on values of L, C and R

For high frequency, capacitor offers :

• more resistance

• less resistance

• zero resistance

• none of these