Tag: electro-magnetism

Quizzes (12) Questions (113)

Questions Related to electro-magnetism

Multiple choice physics electro-magnetism applications of electromagnets transformer transformers

The transformer is used in ................. current circuits.

  1. alternating

  2. directing

  3. no

  4. less
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A transformer consists of two coils - the primary coil and the secondary coil both wound on a soft iron core. If an ac voltage is applied to the primary coil then this will produce a changing magnetic field in the iron core. This induces an alternating voltage in the secondary coil according to electromagnetic induction.
A voltage in the secondary coil occurs only if the magnetic field is changing. Therefore, transformers will only work with ac current only. The transformer is used in alternating current circuits.

Multiple choice physics electro-magnetism applications of electromagnets transformer transformers

Name the material of core in electric bell, electromagnet, d.c. motor, a.c. generator and transformer.

  1. soft iron

  2. hard iron

  3. soft steel

  4. hard steel
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A magnetic core is a piece of magnetic material with a high permeability used to confine and guide magnetic fields in electrical, electro-mechanical and magnetic devices such as electromagnets, transformers, electric motors, generators, inductors, magnetic recording heads, and magnetic assemblies. It is made of ferromagnetic metal such as iron, or ferrimagnetic compounds such as ferrites.
The magnetic field is often created by a coil of wire around the core that carries a current. The presence of the core can increase the magnetic field of a coil by a factor of several thousand over what it would be without the core. The use of a magnetic core can enormously concentrate the strength and increase the effect of magnetic fields produced by electric currents and permanent magnets. 
The properties of a device will depend on the following factors:

  • The geometry of the magnetic core.
  • The amount of air gap in the magnetic circuit.
  • The properties of the core material like permeability and hysteresis.
  • The operating temperature of the core.
  • Whether the core is laminated to reduce eddy currents.

Multiple choice physics electro-magnetism applications of electromagnets transformer transformers

Transformers are used

  1. in DC circuit only

  2. in AC circuits only

  3. in both DC and AC circuits

  4. neither in DC nor in AC circuits
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Transformers work on the principle of voltage induction by the linkage of changing magnetic flux between between the two cores. Changing magnetic flux requires changing/alternating current. 
Transformers are used only in AC circuits. In DC circuits, no alternating/changing magnetic flux is produced to induce voltage in secondary from the primary terminals of the transformers.

Multiple choice physics electro-magnetism applications of electromagnets transformer transformers

How will you  relate the number of turns in the primary coil of a step-down transformer  to that in secondary coil ?

  1. has large number of turns

  2. is very heavily insulated

  3. is very thin

  4. all the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A step down transformer has more turns of wire on the primary coil and less turns of wire on the secondary coil. This makes a smaller induced voltage in the secondary coil. 

Multiple choice physics electro-magnetism applications of electromagnets transformer transformers

In a step down transformer, the number of turns in the primary is always :

  1. greater than the number of turns in the secondary

  2. less than the number of turns in the secondary

  3. equal to the number of turns in the secondary

  4. either greater than or less than the number of turns in the secondary
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In step down transformers, voltage in secondary coil decreases. and we know that 


$\dfrac { { E } _{ s } }{ { E } _{ p } } =\dfrac { { n } _{ s } }{ { n } _{ p } } $

So, number of turns decreases in secondary coil with respect to primary coil.

Multiple choice physics electro-magnetism applications of electromagnets transformer transformers

A transformer changes the voltage

  1. without changing the current and frequency

  2. without changing the current but changes the

    frequency

  3. without changing the frequency but changes the

    current

  4. without changing the frequency as well as the

    current
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A transformers changes an alternating potential difference from one value to another of greater or smaller value using the principle of mutual induction. so, in transformer current and voltage changes but frequency remains same.

Multiple choice physics electro-magnetism applications of electromagnets transformer transformers

Statement A: In a transformer, a large alternating current at low voltage can be transformed into a small alternating current at high voltage
Statement B: Energy in current carrying coil is stored in the form of magnetic field.

  1. A is true but B is false

  2. Both A and B are true

  3. A is false but B is true

  4. Both A and B are false
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Transformer is used to increase voltage and decrease current in the secondary coil with respect to primary coil or vice versa.
Energy in the coil is always stored in the form of magnetic field.