Question

In a step up transformer, primary power is $50\,W$ and output voltage is $100\,V$.If the current in the primary is $1\,A$ then
$\dfrac{\text{Secondary Power}}{\text{Primary Power}} =$

Answer 1

In order to solve this question we need to understand faraday’s law of electromagnetic induction. So according to this law, if there is a magnetic flux change at any loop then an emf would be induced in the loop and it bound the current to flow in direction according to Lenz’s law.

Complete step by step answer:
So if two loops are placed close to each other and one loop is connected to potential difference, now if potential difference varies across the first loop then there would be change in magnetic flux in the second loop which induced the emf in that loop, this is the case with the transformer.

A transformer has two windings, one is primary winding and another is secondary winding, so current change in primary winding induces the emf and hence binds the current to flow in secondary winding.Power of any electrical device is defined as,
$P = VI$
Here, “V” is voltage and “I” is electrical current.

In a step up transformer, voltage across the secondary winding is increased and the current across secondary winding decreases, so the power across secondary winding does not change due to increase and decrease of voltage and current respectively.So the power of the secondary winding is the same as the power of the primary winding.

Hence, $\dfrac{\text{Secondary Power}}{\text{ Primary Power}} = 1$.

Note: It should be remembered that, step up transformer is installed so as to increase the voltage while step down transformer is used to decrease the voltage. In a step up transformer current is less so as to prevent the heating of wires. So electrical transmission in any area is done by using both step up and step down transformers.