Notes, Exercises, Videos, Tests and Things to Remember on Transformer
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A transformer is a device used to convert low a.c. voltage into high a.c. voltage and vice versa. It is of two types: -
A step-up transformer converts low a.c. voltage into high a.c voltage and step-down transformer converts high a.c. voltage into low a.c voltage. The instrument is based on the principle of mutual induction.
Structure: It consists of a rectangular soft iron core made up of laminated sheets. There are two coils which are not connected to one another in any way. These coils are wound on the iron core. One of the coils may be connected to a source of a.c. This coil is called primary coil and the other is called secondary coil.
The e.m.f. of a.c. source applied across the primary coil is called input voltage and e.m.f. induced across the secondary coil is called output voltage.
Principle: When an alternating e.m.f. is applied to the primary coil, a changing current flowing in it produces an alternating magnetic flux in it. This causes to change the magnetic flux linked with the secondary coil. An alternating e.m.f. is then induced in the secondary coil. It is called principle of mutual induction on which transformers are based.
The formula showing the relation between the primary voltage and secondary voltage is as follows: -
No, the transformer can"t change the electromotive force (e.m.f.) of a dry cell.
Transformer is needed during the both cases, either to increase the voltage or to decrease it. Without transformer no change in the voltage of alternating current can be made. That's why the use of alternating current is limited without transformer.
The core of the transformer is laminated just to reduce the loss in input current. When electric current flows in the core of a transformer, the internal current i.e. eddy current (which flows in a circular way) is set up in the body of core. This current has heating effect on the core. The un-laminated core acts as a single block of iron which is heated due to high amount of eddy current. If the core is laminated, the amount of eddy current is highly reduced. Therefore, the core of the transformer is laminated to avoid the heating of a transformer.
Any two differences between step-up transformer and step-down transformer are as follows: -
|Step-up transformer||Step-down transformer|
|It increases the output electricity more than input electricity.||It decreases the output electricity more than input electricity.|
|It increases the magnitude of AC emf.||It decreases the magnitude of AC emf.|
Power of a bulb (P) = 100 W
Potential difference (V) = 220 V
Current electricity (I) = 5 Ampere
According to the formula,
P = V × I
or,100 × X = 220 × 5
Primary voltage (V1) = 220V
Turns in primary coil (N1) = 770
Secondary voltage (V2) = 120V
Turns in secondary coil (N2) = ?
Now, Using formula,
he number of turns in the secondary coil is 420.
The transformer is used in alternating current either to increase the low voltage to high voltage to low voltage according to the required voltage.
When AC supply is given to the transformer, the flux will depend on ______.
Both voltage and current
In transformer, humming sound occurs due to ______.
all of the answers are right
As compared the transformer with AC machines it is more efficient because ______.
Core loss is negligible.
It does not have copper losses.
None of the answers are Correct.
It doesnot have mechanical losses.
The primary and secondary winding of transformers are linked with each other by ______.
not linked at all.
Secondary current of a step down transformer is ______.
equal to the primary current.
double than primary current.
lower than primary current.
Higher than primary current.
The working principle of transformer depends upon ______.
Faraday s law of electromagnetic induction.
Ohm s law.
Fleming s left hand rule.
Lenz s law.