Calculating Power
Calculate the electrical power supplied to a 12 V electrical heater when the current passing through it is 3 A.
36 W
An automobile headlight uses 1500 W of power. How much energy does the headlight convert in 10 seconds?
15 000 J
Calculate the efficiency of a compact florescent light bulb if it produces 30 J of light energy, while 95 J of electrical energy is input.
32%
What is the formula for calculating Power?
P = IV
A 10 V lamp has a current of 2.5 A passing through it. What is the electrical power being consumed by the lamp?
25 W
A battery produces 3 W of power. How much electric energy is delivered in 5 minutes (300 seconds)?
900 J
Calculate the percent efficiency of a motor that produces 4500 J of mechanical energy, while using 6500 J electrical energy.
69%
What is the formula for calculating Energy
E = P x t
My oven has a current of 15 A passing through it when it is connected to 230 V. What is it's energy consumption in a single second?
3450 W
A lamp needs 250 W of power from a generator. How much energy does the lamp convert in 5 seconds?
1250 J
A cell has an input energy of 85 kJ and output energy of 7 kJ. What is its percent efficiency?
8%
What unit is Power measured in?
Watts
A steam iron has a power rating of 1150 W when a current of 5 A passes through it. What would be the potential difference of the supply?
230 V
How much energy does a 60 W light bulb use in 30 minutes?
108 000 J
A car produces 27.5 kJ of useful output energy from 125 kJ of fuel. What is the car’s percent efficiency?
22%
What unit is Energy measured in?
Joules
A student sets up an electrical circuit with two 1.5 V cells in series with a small electrical motor. They measure the current through this motor to be 0.50 A. What is the power consumption of the motor?
1.5 W
A motor converts 100 W of power into 500 J of electrical energy. How long does it take the motor?
5 seconds
A solar panel is capable of absorbing 750 J of light energy every second, and converting 150 J of that energy into electrical energy.
How much energy (in Joules) is ‘wasted’ by the solar panel every second?
600 J
True or false: Most devices have a lower output energy than input energy because some of the energy is destroyed.
FALSE: Energy cannot be created or destroyed, only change forms.