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 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)
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):
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.
|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)|
|siemens / mho||S||Conductance (G)Admittance (Y)|
|Coulomb||C||Electric charge (Q)|
|Ampere-hour||A·h||Electric charge (Q)|
|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)|
|Meter / metre||m||Length (l)|
Parts per million
Units prefix table
1pF = 10-12F
1nF = 10-9F
1μA = 10-6A
1mA = 10-3A
1KΩ = 1000Ω
1MHz = 106Hz
1GHz = 109Hz