Maharashtra State Board · Class 10 · Physics · Chapter 4

Effects of Electric Current — Formula Sheet

Board Formulas

8 formulas

1.Electric Current
$I = \frac{Q}{t}$
Rate of flow of charge. Unit: ampere (A) = 1 C/s.
2.Ohm's Law★
$V = I R$
$V$ : Potential difference (V) · $I$ : Current (A) · $R$ : Resistance (Ω)
For a metallic conductor at constant temperature, V ∝ I.
3.Resistance and Resistivity
$R = ρ \frac{L}{A}$
$ρ$ : Resistivity (Ω·m) · $L$ : Length of conductor (m) · $A$ : Cross-section area (m²)
R depends on length, area and material. ρ is a material constant.
4.Resistors in Series★
$R_{s} = R_{1} + R_{2} + R_{3} + \dots$
Same current through each. Voltages add. Equivalent resistance is larger than largest.
5.Resistors in Parallel★
$\frac{1}{R _{p}} = \frac{1}{R _{1}} + \frac{1}{R _{2}} + \dots$
Same voltage across each. Currents add. Equivalent resistance is smaller than smallest.
6.Electric Power
$P = V I = I^{2} R = \frac{V ^{2}}{R}$
Three equivalent forms. Choose the one using known variables.
7.Joule's Law (Heat Produced)
$H = I^{2} R t$
Heat produced when current I flows for time t through R. Unit: joule.
8.Commercial Energy (kWh)
$E (kWh) = \frac{P ( W ) \times t ( h )}{1000}$
1 unit of electricity = 1 kWh. 1 kWh = 3.6×10⁶ J.