A lamp has a rating of 18V 9W. How much energy is transferred to the bulb in 5 minutes? Calculate the current through it when connected to a 18V supply.
The first question comes from the realisation that the power rating, "9W" represents 9 joules being supplied every second and so can be written as 9J/s and so in 5 minutes (or 300 seconds) the energy supplied is:
9J/s * 300s = 2700J
The second part comes from the equation P=IV and we already have numbers for power and voltage:
9 = 18 * I
I = 9/18 = 0.5Amps
AN
Related Physics GCSE answers
All answers ▸What is the difference between a scalar and a vector?
A lorry is travelling around a roundabout at constant speed. Why is its velocity changing?
I throw a ball straight up with an initial velocity of 2m/s. How high is it after a fifth of a second?
What is terminal velocity?