Electricity 1 — DC Circuits

What electricity costs

continues from lesson 3 — values defined earlier in the course stay live here

ELI5: your meter bills energy (kilowatt-hours), not power — and energy is just power × time. The engine carries the units, so watts × hours comes out as an energy you can read off.

P_{heater} := 1500 W

= 1500 W a space heater

t_{use} := 5 h

= 5 h hours per day

E_{day} = P_{heater} \cdot t_{use}

= 7500 W h energy per day — that's 7.5 kWh

V_{line} := 120 V

= 120 V household line voltage

I_{load} = \frac{P_{heater}}{V_{line}}

= 12.5 A current it draws

✓ pass

I_{load} < 0.8 * 20 A

safe on a 20 A circuit? (80% continuous-load rule — a 15 A one would FAIL)

Real-world hook: this is your electricity bill — and the current draw is why a space heater + hairdryer on one circuit trips the breaker.