Electric Current

Charge in motion (“flow” of charges). Charge in motion (“flow” of charges). Current: The number of electrons that pass a specific point in a circuit in one second Current: The number of electrons that pass a specific point in a circuit in one second I = Q/t I = Q/t Circuit: electric current flows through a closed, continuous path made up of only conducting materials. Circuit: electric current flows through a closed, continuous path made up of only conducting materials.

HIGH LOW Electric Current voltage The reason electric charge flows from one place to another is voltage. a. Voltage is the difference in electrical potential between two places where e - are flowing. b. Voltage is the “push” that makes electric charges move. c. Measured in volts (V).

What provided the “Voltage” in the circuits you made yesterday?

Batteries are e¯ pumps. a. They provide a voltage difference to a circuit. b. Types: wet-cells & dry-cells

Generating Electric Current Electrochemical cell: (battery) changes chemical energy into electric energy. Two types wet cell and dry cell. Electrochemical cell: (battery) changes chemical energy into electric energy. Two types wet cell and dry cell. Thermocouples: a tool that uses differences in temperature to generate electric currents. Thermocouples: a tool that uses differences in temperature to generate electric currents. Generator- next chapter but make alternating current Generator- next chapter but make alternating current

Types of current Direct current: electrons that flow in the same direction in a wire. (DC) Direct current: electrons that flow in the same direction in a wire. (DC) From batteries From batteries Alternating current: electrons that flow in different directions in a wire. (AC) Alternating current: electrons that flow in different directions in a wire. (AC) From Generators From Generators Used in your home Used in your home Transformers change AC to DC Transformers change AC to DC

Measuring Electricity Current: Measured in Amperes or amps (A) Current: Measured in Amperes or amps (A) Voltage: Measured in volts (V) Voltage: Measured in volts (V) Higher voltage, the more work the electrons can do. Higher voltage, the more work the electrons can do.

Measuring Electricity Resistance: the natural force opposing the flow of electrons. Resistance: the natural force opposing the flow of electrons. Measured in ohms Measured in ohms Symbol is Greek letter omega  Symbol is Greek letter omega  Thicker wire- less resistance Thicker wire- less resistance Longer wire- more resistance Longer wire- more resistance Conductors- low resistance Conductors- low resistance Insulators- high resistance Insulators- high resistance

Ohm’s Law The relationship among current, voltage, and resistance. The relationship among current, voltage, and resistance. Ohm’s law states that the current in a circuit is equal to the voltage divided by the resistance Ohm’s law states that the current in a circuit is equal to the voltage divided by the resistance I = V R I = V R V I R

Do the Math A car has a 12 volt system. The headlights are on a 10 amp circuit. How much resistance do they have? A car has a 12 volt system. The headlights are on a 10 amp circuit. How much resistance do they have? Your house uses 120 volts. What amount of current would flow through a 20 ohm resistor? Your house uses 120 volts. What amount of current would flow through a 20 ohm resistor?

Electric power and energy Power: The rate at which electricity does work or provides energy The amount of electric power a device uses to do work is determined by its resistance. Power: The rate at which electricity does work or provides energy The amount of electric power a device uses to do work is determined by its resistance. P = V x I P = V x I (P) power = (V) voltage x (I) current in the circuit. (P) power = (V) voltage x (I) current in the circuit.

Formula for energy Formula for energy E = P x t E = P x t (E) energy used = (P) power x (t) time (E) energy used = (P) power x (t) time The SI unit for energy is a joule. The SI unit for energy is a joule. Kilowatt-hour meters measure the electricity used in your home. Kilowatt-hour meters measure the electricity used in your home. (kWh) (kWh)