Ohm’s law

In this lesson, we will learn:

• Meaning of V, I, and R
• Ohm’s law
• Conventional current vs. electron current

• Ohm’s law relates the voltage, current and resistance in a conductor. It states that the current through a conductor is proportional to the voltage applied across the conductor, and inversely proportional to the resistance of the conductor.
• Voltage (V) is the electric potential difference between two points. It is potential energy per unit charge. It is helpful to think of voltage as the “driving force” or “pressure” that moves charge in a circuit. The unit for voltage is the volt (V).
• Current (I) is the flow of electric charge. The unit for current is the ampere (A).
• Conventional current is the flow of positive charge from high potential to low potential. Conventional current flows from the positive terminal to the negative terminal of a battery or cell.
• Electron current is the flow of electrons, which are a negative charge carrier. Negative charges flow from low potential to high potential, which is from the negative terminal to the positive terminal. Electron current always flows in the opposite direction to conventional current.
• Conventional current is used when working with circuits. Circuits are treated as though positive charges are flowing from the positive terminal to the negative terminal, even though what is actually happening in a circuit is electrons flowing in the opposite direction. Using conventional current rather than electron current is a historical convention.
• Resistance (R) is a measure of how difficult it is for electric charge to flow. The unit for resistance is the ohm ($\Omega$).

Voltage Definition
V = $\large \frac{E_{p}} {q}$
V : Voltage, in volts (V)
E_p : Charge, in coulombs (C)
t : Time, in seconds (s)

Current Definition
I = $\large \frac{q} {t}$
I : Current, in amperes (A)
q : Charge, in coulombs (C)
t : Time, in seconds (s)

Ohm’s Law
V = IR
V : Voltage, in volts (V)
I : Current, in amperes (A)
R : Resistance, in ohms ($\Omega$)

Elementary Charge
e = 1.60 x 10^-19 C
q_proton = e
q_electron = -e