Question

(i). Define ampere in terms of force between two current-carrying conductors.
(ii) What is an ideal transformer?

Answer 1

Hint: Force per unit length between two long parallel conductors is defined by the equation $F = \dfrac{{{\mu _0}}}{{2\pi }}\dfrac{{{I_1}{I_2}}}{r}$ . For an ideal transformer, there will be no energy loss. This implies that an ideal transformer will have an efficiency of 100%.

Complete step-by-step answer:
The force per unit length $F$ between two long current carrying parallel conductors with current ${I_1}$ and ${I_2}$ kept at a distance r is given by $F = \dfrac{{{\mu _0}}}{{2\pi }}\dfrac{{{I_1}{I_2}}}{r}$,where ${\mu _0}$is the magnetic constant or the permeability of free space .The force experienced by both the wires will be equal by newton’s third law . If we keep two long wires carrying 1 ampere of current, 1m apart the force experienced by any one of the wire will be $F = \dfrac{{{\mu _0}}}{{2\pi }}\dfrac{1}{1}$

This leads us to the operational definition of 1 ampere that if the 1-ampere current is flowing between two infinite parallel conductors, kept 1m apart in empty space(which has no other magnetic field present), the force experienced will be exactly $2.7 \times {10^{ - 7}}N/m$ on each conductor.

(ii) A transformer is defined as a passive electrical device that transfers electrical energy from one circuit to another through the process of electromagnetic induction. It uses the principle of mutual induction i.e. an alternating current in one coil can produce an alternating current in a neighboring coil. In real life, the ideal transformer does not exist. Ideal transformers have an efficiency of 100% i.e. there will be no energy loss and the input power will be equal to the output power.

All the magnetic flux that is released from the primary coil will be linked with the secondary coil.

The core of the transformer has no hysteresis loss.
The output resistance of the transformer will be zero
Eddy current is not formed in the core of the transformer.

Note: (i) The force experienced by the conductors also depends on the medium between them. As said earlier the value of ${\mu _0}$ is $4\pi \times {10^{ - 7}}$ only in vacuum. In all other cases $\mu $ is used which shows the magnetic permeability of that medium.
(ii)Hysteresis loss and eddy currents cannot be avoided completely. Thus an ideal transformer does not exist.