# Electric power – problems and solutions

1. Calculate the electric current of a 10 Watt lamp designed for 12 Volt.

__Known :__

Power (P) = 10 Watt

Voltage (V) = 220 Volt

__Wanted :__ Electric current

__Solution :__

Lamp power = 10 Watt = 10 Joule/second

The equation below shows the relation between the electric power (P), electric potential (V) and electric current (I) stated in formula below :

P = V I

Electric current :

I = P / V = 10 / 220 = 1/22 = 0.045 Ampere

2. Calculate the electric power according to the electric circuit below.

__Known :__

Resistor 1 (R_{1}) = 6 Ω

Resistor 2 (R_{2}) = 6 Ω

Electric voltage (V) = 24 Volt

__Wanted :__ Electric power

__Solution :__

**Equivalent resistor :**

R_{1} and R_{2 }are connected in series. The equivalent resistor :

R = R_{1 }+ R_{2 }= 6 Ω + 6 Ω = 12 Ω

The electric current :

I = V/R = 24/12 = 2 Ampere

Electric power :

P = V I = (24)(2) = 48 Watt = 48 Joule/second

3. Calculate the electric current of a 3 kiloWatt designed for 150 Volt.

__Known :__

Electric power (P) = 3 kiloWatt = 3000 Watt

Electric voltage (V) = 150 Volt

__Wanted :__ Electric current (I)

__Solution :__

Relation of the electric power (P), electric potential (V) and electric current (I) stated in formula below :

P = V I

The electric current :

I = P / V

I = 3000 Watt / 150 Volt

I = 20 Ampere