Class 12 Physics Alternating Current Types of Transformers

Types of Transformers

There are 2 types of transformers:-

Step up transformer:-

  1. This transformer amplifies the voltage. The output is higher than the input which is being supplied.
  2. This condition will be true Vs > Vp only when  Ns > Np and Ip < Is.
  3. Vs = (Ns/ Np) Vp
  4. The output of the transformer à  voltage will be high and current will be less.
  5. They are used in the power stations which supply power to the houses.

Step down transformer:-

  1. For Vs < Vp  to be true then  Ns < Np .
  2. Is > Ip so  that (Pintput  = Poutput).
  3. Output is low voltage and high current.
  4. This transformer is used in welding

Problem:- A power transmission line feeds input power at 2300V to a step down transformer with its primary windings  having 4000 turns. What should be the number of turns in the secondary in order to get output power at 230V?


Input voltage , Vp = 2300V

Number of turns in primary coil, Np =4000

Output voltage, Vs = 230V

Number of turns in secondary  coil, Ns

Using (Vp/Vs) = (Np/ Ns)

(2300/230) = (4000/ Ns)

Ns = (4000 x 230)/(2300)

Ns  =400

Hence there are 400 turns in the secondary coil.


Problem:- At a hydroelectric power plant, the water pressure head is at a height of 300m and the water flow available is 100 m3 s−1. If the turbine generator efficiency is 60%, estimate the electric power available from the plant (g =9.8 m s−2 ).


Height of water pressure head, h = 300 m

Volume of water flow per second, V = 100 m3/s

Efficiency of turbine generator, n = 60% = 0.6

Acceleration due to gravity, g = 9.8 m/s2

Density of water, ρ = 103 kg/m3

Electric power available from the plant = η × hρgV

= 0.6 × 300 × 103 × 9.8 × 100

= 176.4 × 106 W

= 176.4 MW

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