Ohm's Law: V = IR
Ohm's law is the fundamental relationship in electrical circuits: V = IR, where V is voltage (volts), I is current (amperes), and R is resistance (ohms, ?). Voltage is electrical potential difference, current is charge flow rate, and resistance is opposition to current flow. This simple equation allows calculating any of the three quantities if the other two are known. For example, with 12V across 100?: I = V/R = 12/100 = 0.12 A = 120 mA. Ohm's law applies to ohmic materials where resistance is constant.
Understanding Electrical Quantities
Voltage is like electrical pressure, measured in volts (V). Current is charge flow, measured in amperes (A). One ampere is one coulomb per second. Resistance opposes current, measured in ohms (?). A perfect conductor has zero resistance; insulators have very high resistance. Common voltages: AA battery is 1.5V, USB is 5V, household outlet is 120V (US) or 230V (Europe), car battery is 12V. Typical phone charger draws about 1-2A. Understanding these quantities is essential for electrical work and electronics.
Applications in Electronics
Ohm's law is the foundation of circuit analysis. Electrical engineers design circuits using this relationship to ensure components receive correct voltage and current. Calculating resistance helps select appropriate resistors. Measuring voltage and current allows fault diagnosis. Ohm's law explains why longer or thinner wires have more resistance and cause voltage drops. It's used in LED calculations, audio systems, power distribution, and all electronics. Combined with Kirchhoff's laws, Ohm's law allows analyzing complex circuits with multiple components and power sources.
Quick Tips
- Always verify units are consistent
- Use scientific notation for very large/small numbers
- Results are approximations — real conditions may vary
Frequently Asked Questions
Voltage is electrical potential difference (like pressure), measured in volts. Current is the flow rate of electric charge, measured in amperes. Voltage causes current to flow through resistance. Think of water: voltage is pressure, current is flow rate.
Resistance is opposition to electric current flow, measured in ohms (?). Resistors limit current. Conductors have low resistance, insulators have high resistance. Resistance depends on material, length, cross-sectional area, and temperature.
Ohm's law applies to ohmic materials where resistance is constant (resistors, simple wires). It doesn't apply to non-ohmic devices like diodes, transistors, or batteries where current-voltage relationship is nonlinear. Temperature can also affect resistance.
Power P = VI. Combined with V = IR, this gives P = I^2R or P = V^2/R. All three formulas are equivalent. Choose based on known quantities. Power is energy per time, measured in watts (W).
With constant resistance, increasing voltage proportionally increases current (I = V/R). Doubling voltage doubles current. This increases power dissipation (P = VI), which can overheat components. Exceeding component ratings causes damage.