lesson
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A 2,000-watt electric kettle can boil water in two minutes, while a 5-watt phone charger takes hours to draw the same amount of electricity.
The difference between them is not how much total energy they can transform, but how fast they move that energy.
What Is Electrical Power?
In physics, electrical power is the rate at which an appliance transfers energy or does work.
Whenever you see the word "rate" in science, think "per second" — power tells you exactly how many joules of energy transform every second.
📊Create a visual comparison diagram between two domestic appliances. Left card: 'Electric Kettle (2000 W)' with an animation of large energy bursts (labeled '2000 J each second'). Right card: 'Phone Charger (5 W)' with a slow, small energy trickle (labeled '5 J each second'). Below both cards, show an equivalence box stating '1 Watt (W) = 1 Joule per second (J/s)'. Clean modern look with white cards (#ffffff), light gray background (#f8f9fa), border (#e6e6e6), bold navy text (#1e2945), and bright accent colors (amber for high power, blue for low power). Responsive layout fitting within 350px width.
Power is measured in watts (W), where one watt equals one joule of energy transferred per second (1 W=1 J/s).
In the 1760s, Scottish engineer James Watt radically improved steam engine efficiency; scientists later named the unit of power after him to honor his work measuring industrial output.
How do we write this relationship as a mathematical equation that connects energy, time, and power?
The Power Formula
Because power measures how much energy moves during a period of time, we divide energy by time:
P=tEorP=tW where P is power in watts (W), E is energy transferred in joules (J), W is work done (energy shifted by electrical forces) in joules (J), and t is time in seconds (s).
📊Create an interactive or static formula triangle diagram for P = E / t. At the top of the triangle is 'E (Energy in Joules, J)'. At the bottom left is 'P (Power in Watts, W)' and bottom right is 't (Time in Seconds, s)'. Include three formula callout badges beneath: 'P = E / t', 'E = P × t', and 't = E / P'. Use a clean modern palette (#1e2945 text, #ffffff cards, light gray background #f8f9fa, blue accent #22b7ff). Responsive layout under 350px width.