What is the unit of electric current?

Which of the following is a semiconductor element?

$B_1, B_2$ and $B_3$ are three identical bulbs connected as shown in the figure. When all three bulbs glow,a current of $3\,A$ is recorded by the ammeter $A$.
$(i)$ What happens to the glow of the other two bulbs when the bulb $B_1$ gets fused?
$(ii)$ What happens to the reading of $A_1, A_2, A_3$ and $A$ when the bulb $B_2$ gets fused?
$(iii)$ How much power is dissipated in the circuit when all three bulbs glow together?

How many electrons will there be in $1.6 \ C$ charge?

If $R_{1}$ and $R_{2}$ are the resistances of filaments of a $400 \ W$ and a $200 \ W$ lamp,designed to operate on the same voltage,then

How are ammeters and voltmeters connected in a circuit? What do they help us measure?