Energy & Power (Edexcel GCSE Physics): Revision Note
Exam code: 1PH0
Energy & Power
Power is defined as the energy transferred per second
Power is measured in watts
Since power is energy transferred per second, the watt can also be defined as 1 joule per second
1 W = 1 J / s
1 kilowatt (1 kW) is equal to 1000 watts, or 1000 joules of energy transferred per second (1 kJ / s)
Calculating Energy Transfers
Power is defined as the energy transferred per unit time:
Power can also be defined as the work done per unit time:
Where:
E or W = The energy transferred, or work done, measured in joules (J)
t = time measured in seconds (s)
P = power measured in watts (W)
This equation can be rearranged with the help of a formula triangle:
Work, power, time formula triangle
Worked Example
Calculate the energy transferred if an iron of power 2000 W is used for 5 minutes.
Answer:
Step 1: List the known values
Power, P = 2000 W
Time, t = 5 minutes = 5 × 60 = 300 s
Step 2: Write down the relevant equation
Step 3: Rearrange for energy transferred, E
Energy transferred = power × time
E = Pt
Step 4: Substitute in the values
E = 2000 × 300 = 600 000 J
Examiner Tips and Tricks
Think of power as “energy per second”. Thinking of it this way will help you to remember the relationship between power and energy
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