In a transformer,the core is made of soft iron to reduce:

$A$ transformer has an efficiency of $80 \%$ and works at $10 \ V$ and $4 \ kW$. If the secondary voltage is $240 \ V$, then the current in the secondary coil is: (in $A$)

If a step-up transformer has a turn ratio of $5$,a frequency of $50 \, Hz$,the root mean square $(RMS)$ value of the potential difference on the primary is $100 \, V$,and the resistance of the secondary winding is $500 \, \Omega$,then the peak value of the voltage in the secondary winding will be (the efficiency of the transformer is $100 \%$).

An ideal transformer has $500$ and $5000$ turns in primary and secondary windings respectively. If the primary coil is connected to a $6\, V$ battery, then the secondary voltage is....$V$

$A$ transformer with a turns ratio $\frac{N_{1}}{N_{2}} = \frac{50}{1}$ is connected to a $120 \ V$ $AC$ supply. If the primary and secondary circuit resistances are $1.5 \ k\Omega$ and $1 \ \Omega$ respectively,find the power output (in $W$).

Which device is used to transmit voltage over large distances and why?