Tag: physics

Questions Related to physics

In an a.c. generator the speed at which the coil rotates is doubled. How would this affect the frequency of output voltage ?

physics effects of electric current electric generator ac generator magnetic effects of electric current

  1. Frequency of maximum output voltage is halved.

  2. Frequency of maximum output voltage is doubled.

  3. Frequency of maximum output voltage remains same.

  4. Insufficient data.

Show answer
Correct Option: B
Explanation:
In an a.c. generator, emf produced is,

    $e=NAB(2\pi v)sin(2\pi v)t$

          where $N=$ no. of turns

                      $A=$ cross- sectional area

                      $B=$ magnetic field.

A frequency of ac, $v=\dfrac{w}{2\pi}$

                    where $w=$ is the speed of rotation

From the above, Frequency of maximum output voltage is directly proportional to speed of rotation of coil.

B. Frequency of maximum output voltage is double.

In an AC generator, maximum number of lines of force pass though the coil when the angle between the plane of coil and lines of force is :

physics effects of electric current electric generator ac generator magnetic effects of electric current

  1. $0^{\circ}$

  2. $60^{\circ}$

  3. $30^{\circ}$

  4. $90^{\circ}$

Show answer
Correct Option: D
Explanation:

Answer is D.

The emf is actually induced by a change in the quantity called the magnetic flux rather than simply by a change in the magnetic field. Magnetic flux is proportional to both the strength of the magnetic field passing through the plane of a loop of wire and the area of the loop. The value of the magnetic flux is proportional to the total number of lines passing through the loop. When the area is perpendicular, that is, at right angles (90 degrees) to the lines, the maximum number of lines passes through the area and the flux is a maximum. When the area is parallel to the lines, no lines pass through the area and the flux is 0.
Hence, maximum number of lines of force passes though the coil when the angle between the plane of coil and lines of force is 90 degrees.

What energy conversion takes place in a generator ?

physics effects of electric current electric generator ac generator magnetic effects of electric current

  1. mechanical energy into magnetic energy.

  2. mechanical energy into chemical energy.

  3. mechanical energy into electric energy.

  4. electrical energy into mechanical energy.

Show answer
Correct Option: C
Explanation:
Answer is C.

The generation of electrical power requires relative motion between a magnetic field and a conductor. In a generator, mechanical energy is converted into electrical energy. The electricity produced by most generators is in the form of alternating current. In general, AC generators, motors and other electrical equipment are simpler, cheaper and more reliable than their DC counterparts.  AC electricity can be easily transformed into higher or lower voltages making it more versatile than DC electricity. 

The essential difference between a d.c. dynamo and an a.c. dynamo is that

physics magnetism and electromagnetism electric generator ac generator magnetic effects of electric current

  1. a.c. has an electromagnet but d.c. has a

    permanent magnet

  2. a.c. will generate a higher voltage

  3. a.c.has slip rings but the d.c. has a commutator

  4. a.c. dynamo hyas a coil wound on soft iron,

    but the d.c. dynamo has a coil wound on copper

Show answer
Correct Option: C
Explanation:

The a.c dynamo has step rings because it changes polarity in every half cycle.

An electrical generator works on the principle of electromagnetic induction.

physics effects of electric current electric generator ac generator magnetic effects of electric current

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

The electric generator works on the principle of Faraday's Law of electromagnetic induction.


Hence, given statement is $True$.

Complete the sentence by using the correct words given in the brackets:

A ________ (generator / transformer/motor/transducer) is a source of electricity that generates large amount of electricity in a power house.

physics effects of electric current electric generator ac generator magnetic effects of electric current

  1. Motor

  2. Generator

  3. Transducer

  4. Transformer

Show answer
Correct Option: B
Explanation:

A generator is a device that converts mechanical energy into electrical energy. It is the source of electricity used to generate large amounts of electricity in power house.

A dynamo 

physics magnetism and electromagnetism electric generator ac generator magnetic effects of electric current

  1. Creates mechanical energy

  2. Creates electrical energy

  3. Converts electrical energy into mechanical energy

  4. Converts mechanical energy into electrical energy

Show answer
Correct Option: D
Explanation:

Generally a small dynamo require a permanent magnet. Using the Faraday's law of induction, rotating a coil of wire and magnetic fields to convert mechanical rotation into a direct electric current. Thus, a dynamo converts mechanical energy to electrical energy.  

A dynamo is used to supply electric current to a small electric bulb, If the number of turns in the coil of this dynamo is doubled, then the voltage in the bulb.

physics magnetism and electromagnetism electric generator ac generator magnetic effects of electric current

  1. Will decrease

  2. Remains unchanged

  3. Will be doubled

  4. Will increase by a factor between 1 and 2

Show answer
Correct Option: C
Explanation:

When the number of turns in the coil increases, the strength of the voltage induced in the coil will also increase as the number of turns and induced voltage are directly proportional to each other.
Therefore, if the number of turns in the coil of this dynamo is doubled, then the voltage in the bulb will also be doubled.

In a DC generator, the ends of the coil are connected to __________.

physics effects of electric current electric generator ac generator magnetic effects of electric current

  1. two slip rings

  2. the split ring commutator

  3. either $(1)$ or $(2)$

  4. None of these

Show answer
Correct Option: B
Explanation:

In a DC generator, the ends of the coil are connected to the split ring commutator.

An electricity generating machine consists of a turbine and a______

physics magnetism and electromagnetism electric generator ac generator magnetic effects of electric current

  1. Dynamo

  2. Core

  3. Heat

  4. Sun

Show answer
Correct Option: A
Explanation:
To generate electricity, we need a turbine & dynamo. Turbine rotates to give mechanical energy to dynamo & dynamo converts it to electrical energy.