How can we measure the current in a circuit?

What is the formula to find electric power $P$?

Define power. State the difference between $1$ watt and $1$ watt hour. Establish the relationship between the commercial unit of electric energy and the $SI$ unit of energy. An electric heater rated $1000 \ W / 220 \ V$ operates for $2$ hours daily. Calculate the cost of energy to operate it for $30$ days at the rate of ₹ $5.00$ per $kWh$.

The resistivity of a material does not change if:

In the circuit diagram shown,the two resistance wires $A$ and $B$ are of the same area of cross-section and same material,but $A$ is longer than $B$. Which ammeter,$A_{1}$ or $A_{2}$,will indicate a higher reading for current? Give a reason.

Who invented the simple battery?