Answer 1

In a step-up transformer, the primary coil is made of thicker wire.

This is because in a step-up transformer the number of turns in the secondary coil is more than the number of turns in the primary coil.

As `E_s/E_p = N_s/N_p > 1` and `E_sI_s = E_pI_p`

`∴ E_s > E_p`

But I_s < I_p. i.e  more current flows through the primary coil. Therefore, one must use a thicker wire in the primary coil as compared to that in the secondary coil.