Question

An electric iron is connected to a $200\;{\text{V}}$ mains supply and draws a current of $4\;{\text{A}}$. What is the power rating of the iron?
A $800\;{\text{W}}$
B $50\;{\text{W}}$
C $106\;{\text{W}}$
D $112\;{\text{W}}$

Answer 1

The above problem is based on the electric power. The electric power depends on the current, voltage and resistance of the electric device. The electric power can be calculated by using the two variables form the current, voltage and resistance.

Solution
The formula to calculate the power of the iron is given as,
$P = V \cdot I$
Substitute $200\;{\text{V}}$ for $V$ and $4\;{\text{A}}$ for $I$ in the above expression to find the power rating of the iron.
$P = \left( {200\;{\text{V}}} \right)\left( {4\;{\text{A}}} \right)$
$P = 800\;{\text{W}}$
Thus, the power rating of the iron is $800\;{\text{W}}$and the option (A) is the correct answer.

Additional Information: The voltage difference is necessary for the flow of charge in the electric circuit. The current is the same as the flow of charge in unit time. The resistance is the property of the material that opposes the flow of the charge in the electric circuit. Mathematically, it is the same as the ratio of the voltage to current. The resistance varies with the cross sectional area of the wire and length of the wire.
The electric power may be active power, reactive power or apparent power.

Note: The above problem can also be solved by using the other formula of electric power. The electric power can also be calculated by using the formula either $P = {I^2}R$ or $P = \dfrac{{{V^2}}}{R}$. The resistance can be found by using the formula $R = \dfrac{V}{I}$. This formula of the resistance is only valid for the Ohmic materials.