ELECTROMAGENTIC INDUCTION

When a numbers of turns in a coil is double without any change in the length of the coil, itself inductance becomes.

• Four times

• Double

• Halved

• Squared

Lenz’s law gives

• Direction magnetic field

• Direction of motion of conductor

• Direction of Induced current

• Direction of current in any electrical circuit

The mutual inductance of a pair of coils is 2H. If the current in one of the coil changes from 10A to zero in 0.1 s, the e.m.f induced in the other coil is

• 2V

• 20V

• 0.2V

• 200V

A dynamo

• Generates mechanical energy

• Generated electrical energy into mechanical energy

• Converts electrical energy into mechanical energy

• Converts mechanical energy into electrical energy

A transformer is used to convert

• Mechanical energy into electrical energy

• Alternating current into direct current

• Direct current into alternating current

• A.C of high voltage and low amperage into A.C of low voltage and high amperage and vice versa.

In a step down transformer the input voltage is 22KV and the output voltage is 550V. The ratio of the number of turns in the secondary to that in the primary is

• 1:20

• 20:1

• 1:40

• 40:1

In a noiseless transformer and alternating current of 2A is flowing in the primary coil. The number of turns in the primary and secondary coils are 100 and 20 respectively. The value of the current in the secondary coil is

• 0.08A

• 10A

• 0.4A

• 5A

In a transformer, the number of turns in the primary and secondary coils are 1000 and 3000 respectively. If the primary is connected across 80V AC, the potential difference across each turn of the secondary will be

• 240V

• 0.24V

• 0.8V

• 0.08V

A person moving with a velocity of 10⁴ m/s enters a magnetic field first at 45⁰ and then at 90⁰ to the field. The forces acting on the proton in two cases are in the ratio.

• √2:1

• 1: √2

• 1: √3

• √3:1

An electron moving with a velocity of 2 x 10⁵m/s enters a magnetic field at an angle of 30⁰ to it. Another electron moving at 10⁵m/s enters the same magnetic field at 60⁰ to it. The forces acting an electron are in the ratio.

• 2:√3

• √3:2

• 1:√3

• √3:1