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 ▸As a student rubs his feet along the carpet in his living room, he becomes charged. After this he places his hand on a metal radiator and receives an electric shock. Explain what charge the student obtains, why, and why he receives a shock.
The cyclist used the brakes to slow down and stop the bicycle. A constant braking force of 140 N stopped the bicycle in a distance of 24 m. Calculate the work done by the braking force to stop the bicycle. Give the unit. (3 Marks)
A hair dryer uses 2000J in 5 seconds when on full power. The power used is?
An electric whisk in a bakery has two motors, each with an average power of 1500W. The whisk is used for 4 hours each day, 7 days a week. Electricity costs 18p per kilowatt-hour. Calculate the cost of the electricity used by the whisk in one week.