Resistance Calculator
Enter voltage and current, or resistivity, length and cross-section, to find resistance and power. V=10V, I=2A → R=5Ω, P=20W.
Input Data
Results
At a glance:Resistance R is a material or component's opposition to electric current, measured in ohms (Ω). Ohm's law states V=IR (V voltage, I current). The resistivity form is R=ρL/A (ρ resistivity, L length, A cross-section). Power is P=V·I=I²R=V²/R. Properties: (1) metal resistance rises with temperature; (2) semiconductor resistance falls with temperature; (3) superconductors have zero resistance at low temperature. Applications: (1) circuit design (current limiting, voltage division); (2) heaters (water heaters, ovens); (3) fuses (overcurrent protection); (4) strain gauges (force sensing); (5) thermistors (temperature sensing).
Formula
Ohm's law: V = I·R
Resistivity: R = ρ·L/A
Power: P = V·I = I²·R = V²/R
Conductance: G = 1/R
$$V = I R, \quad R = \frac{\rho L}{A}, \quad P = VI = I^2 R = \frac{V^2}{R}$$How to Use
- Enter voltage V and current I (Ohm's law mode).
- Or enter resistivity ρ, length L, and area A (resistivity mode).
- The calculator returns resistance R and power P.
Case Studies
Household circuit and fuses
Hong Kong homes: 220 V RMS, 13 A sockets. A 1000 W water heater draws I=P/V=4.5 A; a 2 mm² copper wire safely carries 15 A.
Fuses blow to protect the circuit on overcurrent. The 13 A plug fuse is selected by load current.
Miniature circuit breakers (MCB) of 16 A, 20 A, 32 A are reusable and standard in HK distribution boards.
Content review: Calculatorism Science Team. Results are for reference only; please refer to the relevant authorities for the official figures.