Ohm’s law defines a linear relationship between the voltage and the current in an electrical circuit. The DC current flow through a resistor is set by the resistor’s voltage drop and the resistor’s resistance. With water flow analogy we can imagine the electric current as water current through pipe, the resistor as a thin pipe that limits the water flow, the voltage as height difference of the water that enables the water flow. Ohm’s law
Ohm’s law definition :- The resistor’s current I in amps (A) is equal to the resistor’s voltage VR=V in volts (V) divided by the resistance R in ohms (Ω)
V is the voltage drop of the resistor, measured in Volts (V). Sometimes E is used instead of V . E denotes electromotive force. I is the electrical current fl0wing through the resistor, measured in Amperes (A) R is the resistance of the resistor, measured in Ohms (Ω)
Voltage calculation
When we know the current and resistance, we can calculate the voltage. The voltage V in volts (V) is equal to the to the current I in amps (A) times the resistance R in ohms (Ω): Resistance calculation
When we know the voltage and the current, we can calculate the resistance. The resistance R in ohms (Ω) is equal to the voltage V in volts (V) divided by the current I in amps (A)
Since the current is set by the values of the voltage and resistance, the Ohm’s law formula can show that: If we increase the voltage, the current will increase.
If we increase the resistance, the current will reduce.
Example =1 Find the current of an electrical circuit that has resistance of 50 Ohms and power supply of 5 Volts. Solution:V = 5V
R = 220Ω
I = V / R = 5V / 220Ω = 0.02A = 22 mA.
Unit Name Unit Symbol Quantity.

 Unit Name Unit Symbol Quantity Ampere (amp) A Electric current (I) Volt V Voltage (V, E)Electromotive force (E)Electric potential (φ) Ohm Ω Resistance (R)Impedance (Z) Watt W Electric power (P) Decibel-milliwatt dBm Electric power (P) Decibel-Watt dBW Electric power (P) Volt-Ampere-Reactive VAR Reactive power (Q) Volt-Ampere VA Apparent power (S) Farad F Capacitance (C) Henry H Inductance (L) siemens / mho S Conductance (G)Admittance (Y) Coulomb C Electric charge (Q) Ampere-hour A·h Electric charge (Q) Joule J Energy (E) Kilowatt-hour kWh Energy (E) Electron-volt eV Energy (E) Ohm-meter Ω∙m Resistivity (ρ) siemens per meter S/m Conductivity (σ) Volts per meter V/m Electric field (E) Newtons per coulomb N/C Electric field (E) Volt-meter V·m Electric flux (Φe) Tesla T Magnetic field (B) Gauss G Magnetic field (B) Weber Wb Magnetic flux (Φm) Hertz Hz Frequency (f) Seconds s Time (t) Meter / metre m Length (l) Square-meter m2 Area (A) Decibel dB Parts per million ppm

Units prefix table

 Prefix PrefixSymbol Prefix factor Example pico p 10-12 1pF = 10-12F nano n 10-9 1nF = 10-9F micro μ 10-6 1μA = 10-6A milli m 10-3 1mA = 10-3A kilo K 10 3 1KΩ = 1000Ω mega M 10 6 1MHz = 106Hz giga G 10 9 1GHz = 109Hz