# 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

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

Known :

Resistor 1 (R1) = 6 Ω

Resistor 2 (R2) = 6 Ω

Electric voltage (V) = 24 Volt Wanted : Electric power

Solution :

Equivalent resistor :

R1 and R2 are connected in series. The equivalent resistor :

R = R1 + R2 = 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

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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