Question

An ideal transformer has \[500\] and \[5000\] turns in primary and secondary winding respectively. If primary coil is connected to a $6V$ battery then the secondary voltage is:
$\begin{align}
  & \text{A}\text{. 60V} \\
 & \text{B}\text{. Zero} \\
 & \text{C}\text{. 0}\text{.6V} \\
 & \text{D}\text{. 6V} \\
\end{align}$

Answer 1

Hint: The transformer is an electrical instrument used to increase or decrease the voltage of a given ac source. If the transformer is used to increase voltage of input signal then it is called step-up transformer and if used to decrease then it’s called step down transformer. Transformer only works on a source but not works in a dc-source because to produce induced emf in the secondary coil the current in primary coil must change. But in dc-source the voltage is constant which will not induce the emf in the secondary coil.

Complete answer:
The transformer uses the principle of mutual induction. When two coils placed close to each other and the magnetic flux linked with one coil changes, then an induced emf is produced in the second coil. This process is called mutual induction. This induced emf in the second coil exists as long as the magnetic flux linked to the first coil changes. The first coil to which is connected to the ac-source is called primary coil and the second coil in which the emf is induced due to the first coil is called secondary coil.
The transformer uses the principle of mutual induction to produce the induced emf in the secondary coil. So to produce the induced emf in the secondary coil the source in the primary coil should be ac.
But in the given question the primary coil is connected to a $6V$ battery which is a dc source. So there will be no flux change and no induced emf in the secondary coil.

So, the correct answer is “Option b”.

Note:
Magnetic flux: the magnetic flux through any surface placed in a magnetic field is the total number of magnetic lines of force crossing this surface perpendicularly. It is measured as the product of the component of magnetic field parallel to the normal to the surface and the surface area, and is given by
$\phi =\overrightarrow{B}.\overrightarrow{A}$
The unit of magnetic flux is “Weber(Wb)”. $1Wb=1tesla\times 1{{m}^{2}}$
Dimension of magnetic flux $\left[ M{{L}^{2}}{{T}^{-2}}{{A}^{-1}} \right]$.