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 ▸Explain how resonance occurs for a driven oscillating system and describe the effect of damping on the resonant frequency.
An ideal gas within a closed system undergoes an isothermal expansion from an initial volume of 1m^3 to 2m^3. Given that the initial pressure of the gas is 10^5 Pa, find the final pressure of the gas following the expansion.
The LHC accelerates protons to a speed of 0.999999991c around a 27km ring. Due to relativistic effects, their mass increases. Given that the magnetic fields used are 8T, calculate this mass. What is the total energy of an LHC beam containing 3e14 protons?
What is the definition of a moment?