If a bulb has a current of 20mA and voltage of 5V, and the current cost of electricity is £3 for a kW/hour. How much money would you spend to power the bulb for 8 hours? Are these good estimates for the current, voltage and cost of electricity?
Well we know that the power of the bulb is given by P = IV. Therefore the power = (20 x 10-3 Coulomb per second) * (5 Joules per Coulomb) = 100 x 10-3 Joules per second = 0.1 W.
So the bulb uses 0.1 Joules of energy per second or 0.1 Watts.
To power the bulb for one hour you need 0.1 W = 0.0001kW
Therefore 0.0001 * 300 pence = 0.03 pence per hour.
So for 8 hours it would cost 0.24 pence.
AV
Related Physics A Level answers
All answers ▸An engineering student found that the Youngs modulus of an alloy was 2.8 x 10^11 Pa. The 1.5m wire of the allow increased in length by 0.24% during an experiment. Calculate the stress on the wire.
What is the angular velocity of a person standing on the surface of the earth. Give your answer in radians per second
A ball is hit horizontally at a height of 1.2 m and travels a horizontal distance of 5.0 m before reaching the ground. The ball is at rest when hit. Calculate the initial horizontal velocity given to the ball when it was hit.
How to we work out the speed of an object at a certain point in its trajectory?