Electric Current. Ohm’s Law

Potential Difference

• Electricity is made up of charged particles that carry energy from one place to another.

• Voltage is a measure of electric potential energy.• Potential Difference is difference in the amount of

potential (charge), difference in potential energy between two places.

• A voltage difference means there is energy that can be used to do work.

• Symbol: V• Units: volts (V)

Electric Current

• Electric current is the flow of electric charge. Electric current comes from the motion of electrons or other charged particles.

• It’s a flow of electrons through a wire or conductor. The amount of current is equal to the number of electrons passing a point in a given time.

• Symbol: I• Unit: amperes (A), 1 ampere = 1 coulomb of charge

per second, 1 coulomb is equal to 6.24 x 10¹⁸ electrons, 6.24 billion billion electrons.

• I = , where I –current (A), Q –charge (C), t-time (s)

Electric Current

• In which direction do electrons flow?• Electrons flow from area of high potential

energy to areas of low potential energy, from a high concentration of electrons to low concentration of electrons.

Electric Current

• What keeps a current moving through a circuit?

• Must maintain a potential difference (continuous difference in the amount of charge).

• Examples: battery, home’s electric system (not static electricity).

Voltage and Current

• How are voltage and current different?• Current is what actually flows and

does work. Voltage differences provide the energy that causes current to flow.

What Does Voltage Mean?

• A voltage difference of 1 volt allows 1 amp of current to do 1 joule of work in 1 second. The work done per unit of time is called power, and 1 joule per second equals 1 watt of power. Therefore, voltage is the power per amp of current that flows. Every amp of current flowing out of 1.5-V battery carries 1.5 watts of power.

• The higher the voltage, the more power is carried by each amp of electric current.

Electric Circuit

• Electric Circuit is a complete path through which electricity travels.• It’s a closed path through which

electrons can flow continuously.

Resistance

• Resistance is tendency for material to oppose (resist) the flow of electrons.• Symbol: R• Units: ohms (Ω) Greek symbol

omega

Resistance

• What factors affect resistance?• 1. Nature of material (conductor or insulator).

Examples, low resistance metals and high resistance plastics and rubber.

• 2. Thickness (thin wires – higher resistance, think wires – lower resistance).

• Length (long wires – higher resistance, short wires – lower resistance).

• Temperature (higher temperature – higher resistance)

Ohm’s Law

• Ohm’s Law: mathematical relationship between potential difference, current, and resistance.

• Potential Difference = Current x Resistance• V = I x R• Units: Volts = amperes x ohms or V = A x Ω• I = R =

Circuit Symbols

Circuit Symbols

• Describing Circuits with words: “a light bulb and a 1.5-Volt D-cell.“

• Describing Circuits with drawings: