Electric Current and Circuits Physics

Current The flow of charges Rate at which electric charges (+ or - ) pass through a conductor – Charge passes per second Symbol is I Units are Amps (A)* – 1 A means 1 C of charge passes every second

Current Flow of charge needs a push – Supplied by change in voltage or potential difference Charge flows from high to low PE

Suppose A has a potential of 12 V and B has a potential of 2 V. There is a potential difference. A has higher potential energy than B, and it means there is voltage. Potential difference is V A - V B = = 10 V.

Suppose C and D has a potential of 7 V. There is no potential difference between two plates. The potential difference is V C - V D = = 0 V. No voltage means no flow of charge.

Check for Understanding Why can a bird sit on a power line? If there are voltage or potential difference, then the current starts to flow from high voltage to low voltage. But when a small bird sits on the power line, both feet are on the same voltage line! Therefore, there are no potential difference between these two feet.

What will happen if something pushes the charge from the bottom plate to the upper plate E in the diagram? -potential difference generated -there will be continuous flow of charge. -This is how a battery works; it takes "+" charge from bottom and push it to top.

Circuit The system like above, a closed loop of current, is called an electric circuit.

Simple Circuit Contains a light bulb, battery, and wire

Circuits We can draw circuits using symbols

Drawing Circuits Light bulbs are drawn as resistors since they affect the flow of charge

Resistance Determines flow of electric charge Varies based on material High resistance – Glass, plastics, wood Low resistance – Gold, silver, copper (metals) Symbol is R Unit is the ohm (Ω)

Check for Understanding Draw the Schematic

Check for Understanding Draw the Schematic

Ohm’s Law Discovered by Georg Simon Ohm Found relationship between current, voltage and resistance V = IR

Sample Problem What is the current of a circuit that has 3 V and 0.5 Ω of resistance?

Class work What is the voltage if current is 0.5 A and resistance is 0.8 Ω? What is the resistance if voltage is 3.0 V and current is 1.5 A? A flashlight that is powered by 3 Volts and uses a bulb with a resistance of 60 Ω. What is the current through the bulb?

Closing What is the relationship between current and a circuit?

Homework Study for Quiz – Electrostatics- notes – Electric potential energy- notes – Electric potential/voltage- notes – Electric field- draw field lines – Coulomb’s Law- solve problems – Current- notes – Circuits- notes and drawing practice – Ohm’s law- more practice problem