Factors that affect the efficiency
The heating effect of current in a coil.
Power is lost as heat I₂R whereby I is the current flowing through the coil and R is the resistance of the coil

Methods to increase the efficiency
Use thick copper wires of low resistance. Use coolant to decrease the temperature of the transformer.

Heating effect of induced eddy currents
In the iron core. When the magnetic field in the iron core fluctuates, eddy currents are generated in the iron core.

Methods to increase the efficiency
Use a laminated iron core whereby each layer is insulated with enamel paint to prevent the flow of eddy currents. The high resistance between layers of the iron core decrease the prevalence of eddy currents and heat.


Magnetization of the iron core.
The energy used in the magnetization and de-magnetization of the iron core each time current changes its direction is known as hysterisis. This energy is lost as heat which subsequently heats up the iron core.

Methods to increase the efficiency
Use a soft iron core that is easily magnetized and de-magnetized.

Flux leakage.
Some of the induced magnetic flux from the primary coil is not transmitted to the secondary coil, therefore the e.m.f in the secondary coil is decreased.
The secondary coil(windings) are intertwined tightly with the primary coils. The iron core should form a closed loop.

Methods to increase the efficiency
The secondary coil (windings) is intertwined tightly with the primary coils. The iron core should form a closed loop.

[This image is original released under GNU Free Documentation license ]

What is transformer?
Transformer is a device that is used to raise or lower down the potential difference of an alternating current.

Function:
The function of a transformer is to increase or decrease the potential difference of an alternating current supply.

Structure and Technical Terms
1. A transformer consist of 3 parts, namely

1. The primary circuit
2. The core
3. The secondary Circuit

[This image is released under the GNU Free Documentation License.]

Primary Circuit:
The primary circuit is the circuit that connected to the input energy source. The current, potential difference and coil (winding) in the primary circuit are called the primary current (Ip), primary potential difference (Vp) and primary coil respectively.

Core:
The core is the ferromagnetic metal wound by the primary and secondary coil. The function of the core is to transfer the changing magnetic flux from the primary coil to the secondary coil.

Secondary Circuit:
The secondary circuit is the circuit that connected to the output of the transformer. The current, potential difference and coil (winding) in the secondary circuit are called the secondary current (Is), secondary potential difference (Vs) and secondary coil respectively.

Working Principle of A Transformer

1. A transformer consists of a primary coil and a secondary coil wound on a soft iron core.
2. When an alternating current flows in the primary coil, a changing magnetic flux is generated around the primary coil.
3. The changing magnetic flux is transferred to the secondary coil through the iron core.
4. The changing magnetic flux is cut by the secondary coil, hence induces an e.m.f. in the secondary coil.
5. The magnitude of the output voltage can be controlled by the ratio of the number of primary coil and secondary coil.

Types of Current in A Transformer
The current in the primary circuit must be alternating current because alternating current can produce changing magnetic flux. A changing magnetic flux is needed to induce e.m.f. in secondary coil.

The induced current in secondary is also an alternating current. The frequency of the alternating current in secondary coil is same as the frequency of the primary current.

The alternating in the secondary circuit can be converted into direct current by using a pair of diode.

Symbol of A Transformer

The figure on the left shows the symbol of a transformer. The 2 lines in between the coil denote the core.

Types of Transformer

Step-up transformer
A step-up transformer is one where the e.m.f. in the secondary coil is greater than the e.m.f. in the primary coil. It is used to increases the potential difference. The number of windings in the secondary winding is greater than the number of windings in the primary coil. The current in the primary coil is greater than the current in the secondary coil.

Step-down transformer
Conversely, a step-down transformer is one where the e.m.f. in the secondary coil is less than the e.m.f. in the primary coil. It is used to reduce the potential difference. The number of windings in the primary winding is greater than the number of windings in the secondary coil. The current in the primary coil is lesser than the current in the secondary coil.

Calculation of Potential Difference Change

{{V_s } \over {V_p }} = {{N_s } \over {N_p }}

Vp = input (primary) potential difference
Vs = output (secondary) potential difference
Ip = input (primary) current
Is = output (secondary) current

Calculation of Current Change
Ideal Transformer

V_p  \times I_p  = V_s  \times I_s

Non-ideal transformer

Efficiency = \frac{{V_s I_s }}{{V_p I_p }} \times 100\%

Vp = input (primary) potential difference
Vs = output (secondary) potential difference
Ip = input (primary) current
Is = output (secondary) current

Physics Animation
Applet
Transformer - Molecular Expression
Transformer - ngsir.netfirms.com
Electromagnetic Oscillating Cirecuit - Walter Fendt



External Link
Transformer - physics.kenyon.edu