Tag: applications of electromagnets

Questions Related to applications of electromagnets

A transformer

physics electro-magnetism applications of electromagnets transformer transformers

  1. Converts AC to DC

  2. Converts DC to AC

  3. Increases or decreases (step up or step down) AC voltage

  4. Increases or decreases (step up or step down) DC voltage

Show answer
Correct Option: C
Explanation:

C

Transformer is a static device which transforms electrical energy from one circuit to another and with the help of mutual inductor between two windings. The transformer may be step up or step down. A transformer that increases voltage from primary to secondary (more secondary windings turns than primary winding turns) is called step up transformer. Conversely a transformer designed to do just the opposite is called step down transformer. 

The purpose of a transformer is to do which of the following?

physics electro-magnetism applications of electromagnets transformer transformers

  1. Change voltage

  2. Reduce resistance

  3. Decrease heat transfer

  4. Increase magnetic fields

  5. Reverse current flow

Show answer
Correct Option: A
Explanation:

A transformer is based on the principle of mutual inductance , and it is used to change the alternating voltage . The transformer which increases the voltage is called step-up transformer , and which decreases is step-down transformer .

Complete the given statement, in order for a transformer to work:

physics electro-magnetism applications of electromagnets transformer transformers

  1. the magnetic field must be changing.

  2. the magnetic field must not change.

  3. it must be connected to a direct current source.

  4. the primary coil and the secondary coil must have different numbers of turns.

  5. the number of turns in the secondary coil must be greater than the number of turns in the primary coil.

Show answer
Correct Option: A
Explanation:

The transformer works on the principle of mutual induction. The voltage in one coil changes to change the magnetic field that it creates. This changing magnetic field causes a flux change in the secondary coil, which would create an induced emf in the coil. Thus it is necessary to have a changing magnetic field in a transformer to cause induction in secondary coil.

Fill the vacant spaces with appropriate terms. The _______ going into a transformer is equal to the _______ going out of the transformer.

physics electro-magnetism applications of electromagnets transformer transformers

  1. power, voltage

  2. power, power

  3. current, current

  4. voltage, voltage

  5. voltage, power

Show answer
Correct Option: B
Explanation:

Working of transformer is based on the conservation of power i.e no power is lost inside the transformer.

Thus total power going into a transformer is equal to the total power going out of the transformer.

In a transformer, the immediate cause of the induced alternating current in the secondary coil is:

physics electro-magnetism applications of electromagnets transformer transformers

  1. a varying magnetic field

  2. a varying electric field

  3. the iron core of the transformer

  4. a motion of the primary coil

Show answer
Correct Option: A
Explanation:

Transformer works on the basis of electromagnetic induction, which is produced by changing magnetic flux. In a transformer both the coils are fixed and not moving thus, the change in magnetic flux is because of change in magnetic field.

A transformer is used to:

physics electro-magnetism applications of electromagnets transformer transformers

  1. convert alternating current to direct current

  2. convert direct current to alternating current

  3. convert mechanical energy to electrical energy

  4. transform alternating current voltage

Show answer
Correct Option: D
Explanation:

In a transformer the change in the current in primary coil produces the change in the current in secondary coil because of electromagnetic induction. 

Thus, transformer changes the AC voltage.

A transformer uses iron core to .................... power loses.

physics electro-magnetism applications of electromagnets transformer transformers

  1. Minimise

  2. Maximum

  3. Remains same

  4. None of these

Show answer
Correct Option: A
Explanation:

iron core is basically used to minimise flux leakage so that energy losses can be minimise.

The ratio of secondary to the primary tums in a transformer is $3:2.$ If the power out put be $P$, then input power, neglecting all losses, must be equal to:

physics electro-magnetism applications of electromagnets transformer transformers

  1. $5\ P$

  2. $1.5\ P$

  3. $P$

  4. $\dfrac {2}{5}\ P$`

Show answer
Correct Option: B
Explanation:

Power= $VI$

For secondary $P _2=V-2I _2=\cfrac { { T } _{ 2 } }{ { T } _{ 1 } } { V } _{ 1 }\times \cfrac { { T } _{ 1 } }{ { T } _{ 2 } } { I } _{ 1 }={ V } _{ 1 }{ I } _{ 1 }$
Hence, $P _2=V _1I=P$
Power is same in transforming primary and secondary.

An electric motor requires $220\ V$ of alternating current to run but the supplied alternating voltage is $100\ V$. Then the device used to run the motor is 

physics electro-magnetism applications of electromagnets transformer transformers

  1. Diode

  2. Transistor

  3. Tranformer

  4. Capacitor

Show answer
Correct Option: A

The efficiency of a transformer is

physics electro-magnetism applications of electromagnets transformer transformers

  1. $\eta$ < 1

  2. $\eta = $ 1

  3. $\eta$ > 1

  4. $\eta = $ 0

Show answer
Correct Option: A
Explanation:

efficiency of a transformer $=\frac { Power _{ output } }{ { Power } _{ input } } $ for having efficiency >1 is not allowed by law of conservation of energy and e$=$1 is only for cases.
so e<1.