Question

An electric iron of heating element of resistance 88 $\Omega$ is used at 220 volt for 2 hours. The electric energy spent, in unit, will be

• A. 0.8
• B. 1.1
• C. 2.2
• D. 8.8

Answer 1

Answer: (B)

The electric power required to operate a device is the input voltage times the current required.
P = VI
where
P = electric power
V = voltage used
I = current in amperes
VI is V times I
Electric power is measured in watts. The electrical energy used is the electric power times the time. That is, E = Pt. If we measure the electric power as kilowatts and the time as hours, we get the energy used by an electrical system in terms of kilowatt-hours. That is the unit of measurement the electric company uses when determining our bill.
In this case, th electric iron of resistance 88 is used at 220 volt for 2 hours.
The power P = VI, substituitng I=V/R we get, $P=\frac{V^2}{R}=\frac{{220}^2}{88}=550W=0.55kW$.
Therefore, energy spent = E = Pt = $0.55kW\times 2hrs=1.1units$.
Hence, the energy spent is 1.1 units.