Chapter 11 · Physics
Electricity
The circuit lab here does not animate a picture; it solves the circuit. Resistances are combined by the correct rules, Ohm's law gives the current, and the V–I graph is plotted from the computed values.
Circuit Lab — Ohm's Law, Series & Parallel
Change the cell and resistances; current, voltage drops, power and heat are recomputed from V = IR and H = I²Rt.
- Rs = R₁+R₂+R₃
- 22.00 Ω
- Total current I
- 0.273 A
- V₁ / V₂ / V₃
- 1.09 / 1.64 / 3.27 V
- I₁ / I₂ / I₃
- 0.27 / 0.27 / 0.27 A
- Power P = VI
- 1.64 W
- Heat in 10 min
- 982 J
- Energy
- 0.00027 kWh
Formula sheet
Electric current
I = Q/t
1 ampere = 1 coulomb per second.
Potential difference
V = W/Q
1 volt = 1 joule per coulomb.
Ohm's law
V = IR
At constant temperature, current is proportional to potential difference.
Resistance of a conductor
R = ρl/A
Resistance increases with length and decreases with area of cross-section.
Series combination
Rs = R₁ + R₂ + R₃
Same current through each resistor; voltages add.
Parallel combination
1/Rp = 1/R₁ + 1/R₂ + 1/R₃
Same voltage across each; currents add.
Electric power
P = VI = I²R = V²/R
Unit watt; commercial unit of energy is kWh.
Joule's heating
H = I²Rt
Heat produced in a resistor in time t.