Which of the following acts as a circuit protection device?

Find the potential at point $x$ in the given circuit. (in $, V$)

The current from the battery in the circuit diagram shown is .............. $A$.

When electric bulbs of same power,but different marked voltage are connected in series across the power line,their brightness will be:

If three bulbs $60\,W$,$100\,W$ and $200\,W$ are connected in parallel,then

The figure shows three similar lamps $L_1, L_2$,and $L_3$ connected across a power supply. If the lamp $L_3$ fuses,how will the brightness emitted by $L_1$ and $L_2$ change?