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 = 𝑸 𝒕 , 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 = 𝑽 𝑹 R = 𝑽 𝑰

Circuit Symbols

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