Revise: Electrical Energy, Power and Heating Effect of Electric Current

V = ε − Ir.

ε=12V,I=2A,r=0.5Ω → V=11V.

Series: EMFs add. Parallel (identical): EMF unchanged, r_total=r/n.

Three 1.5V cells in series → 4.5V.

P = VI = I²R = V²/R. E = Pt.

V=12V,I=3A,t=10s → P=36W, E=360J.

H = I²Rt — heat grows with the square of current.

I=2A,R=10Ω,t=60s → H=2400J.

R = V²/P — designs a heating element for a target power.

P=1000W,V=220V → R=48.4Ω.

Terminal voltage drops further under heavier current draw.

A car battery's voltage dips while cranking the starter.

Series for more voltage; parallel for more current capacity.

Flashlights stack cells in series for enough voltage.

Power is a rate; energy is a total amount.

Electricity bills charge for kWh = kW × hours.

Doubling current quadruples heat generated.

Why wiring is rated for maximum current, not voltage.

At fixed voltage, lower resistance means MORE power.

A kettle is designed with low resistance to heat fast.