Electricity is an essential topic in physics, and it involves understanding how electric currents, voltage, and resistance work together. In this chapter, we’ll cover the basic formulas and principles that help explain electricity in simple terms.
Notations Explained
- I = Current (S.I unit: Ampere, A)
- Q = Charge (S.I unit: Coulomb, C)
- t = Time (S.I unit: Seconds, s)
- W = Work Done (S.I unit: Joules, J)
- V = Voltage or Potential Difference (S.I unit: Volt, V)
- R = Resistance (S.I unit: ohm, Ω)
- ρ = Resistivity (S.I unit: ohm meter, Ω m)
- l = Length (S.I unit: meter, m)
- A = Area (S.I unit: meter square, m2)
- P = Power (S.I unit: watt, W)
- H = Heat (S.I unit: Joules, J)
Relationship Between Current (I), Charge (Q), and Time (t)
Main Formula: I = Q / t
Derived Formulas:
- Q = It
- t = Q / I
Relationship Between Voltage (V), Work (W), and Charge (Q)
Main Formula: W = VQ
Derived Formulas:
- V = W / Q
- Q = W / V
- W = VIt
Ohm's Law
Main Formula: V = IR
Derived Formulas:
- I = V / R
- R = V / I
Resistivity and Resistance
Main Formula: R = ρl / A
Derived Formulas:
- ρ = RA / l
- A = ρl / R
- l = RA / ρ
Resistance in Series and Parallel
Resistance in Series
In series, the current is the same across all resistors, but the voltage differs:
Rs = R1 + R2 + ... + Rn
Resistance in Parallel
In parallel, the voltage is the same across all resistors, but the current differs:
1/Rp = 1/R1 + 1/R2 + ... + 1/Rn
Heating Effect of Electric Current
Main Formula: H = VIt
Derived Formulas:
- H = I2Rt
Other Important Conversions
- 1 mA = 10–3 A (mA - milliampere)
- 1 µA = 10–6 A (µA - microampere)
- 1 kWh = 1000 watts × 3600 seconds = 3.6 × 106 watt-seconds = 3.6 × 106 Joules (J)
Download the Complete Formula List
If you want all these formulas in one document, download the complete formula list from the link below:
Download Formula List for Chapter - Electricity