1. Electricity and Circuits
Moving Charges

2. Current
The amount of charge that passes a point in space in a given amount of time
Units are Amperes
1 Ampere = 1 Coulomb/second
No current flows unless there is a voltage difference across the circuit

3. Resistance
A property of a material that hinders the flow of current through it
Units are Ohms (Ώ)
Insulators
Current cannot flow through
High resistance
Conductors
Current flows easily
Low resistance

4. What is a circuit? There must be a voltage source (e.g. battery)
Provides the potential difference to drive the charges
Charges must move around a complete loop

5. Parts of a Circuit Internal circuit External circuit
What is inside the voltage source
External circuit
What is outside the voltage source

6. Roles of the Battery Provides energy
Converts chemical potential energy stored in bonds to electrical potential energy
Pumps the charge from the - to + terminal
Does work against the electric potential
Maintains a potential difference across the external circuit

7. Anatomy of a Light Bulb
The base of the bulb is electrically isolated from the sides
Current has to flow through the thin filament which has moderately high resistance
The filament heats up until it glows because of the resistance
The glass globe contains a vacuum so that the filament doesn’t react with the air and burn out

8. Find 4 Ways to Light the Light Bulb
High potential
Low potential
Remember you have to go from the positive to the negative end of the battery!

9. Which ones will work?

10. Which ones will work?

11. Electricity and Circuits
Electric Cell
– a device that is a source of electric current because it has a voltage (potential difference) between _the terminals (the positive and negative ends. The charge is separated chemically to produce an electric potential difference.

12. Battery Battery – a combination of cells put
together to produce a _higher voltage_.
The size of the battery corresponds to
___how much energy it holds______ (this is NOT the
same as voltage)! 

13. Building Circuits -3 components
A source (this really means a source of electrons)
A load (this is what is causes charge to “build up” in a circuit)
Examples:
A wire (this creates a closed loop between the load and the source so that electrons can “flow”

14. Current and Circuits Conventional Current
The direction positive charges would flow in the circuit
Yes, we do know NOW that it is really electrons that move through a wire!
Ben Franklin thought it was positive charges that flow and his convention stuck
Conventional current moves from the positive terminal of the battery to the negative one.
In the real world electrons move from the negative terminal of the battery through the external circuit to the positive terminal

15. Inside the Wire Without an electric field, electrons move randomly
Motion is collisional (bumper cars!)
In any given period of time as many electrons cross through a cross sectional area going one way as going the other
No net current

16. Inside the Wire With an electric field
Motion is still collisional (bumper cars!)
Motion in the direction of the field is favored
In any given period of time more electrons go through a cross sectional area going with the field than going the other way
Net current created
Current is the same everywhere in a series circuit
No place where charge builds up in the circuit

17. Turning on the Switch
Electric Field is felt everywhere at close to the speed of light
Charges start moving in response to the electric field (move to lower potential) everywhere at once
Actual drift velocity of electrons is slow (1 m/s)
Light bulb lights immediately because electrons within the filament start to move

18. Copyright© by Holt, Rinehart and Winston. All rights reserved
Copyright© by Holt, Rinehart and Winston. All rights reserved. Terms of use. Privacy Policy.
Copyright© by Holt, Rinehart and Winston. All rights reserved. Terms of use. Privacy Policy.
Copyright© by Holt, Rinehart and Winston. All rights reserved. Terms of use. Privacy Policy.
Circuit Symbols

19. Drawing a Circuit Diagram
Battery
Long line is positive
Switch
Usually draw open
Wires
Drawn with perpendicular lines

20. Series and Parallel Circuits
Series circuits have a single loop
Parallel circuits have several possible loops
Current is split between the loops
Overall resistance is lower because there are more paths for current to flow through
Series Parallel

21. Potential Changes in the Circuit
Going through a wire
makes little change in potential
Battery increases potential
Potential drops in
external circuit
Potential drops across each
device in the circuit
Potential gain in battery = - Potential loss in circuit

22. Which one has the brighter lamps?
Series Parallel

23. Relating the Variables

24. Electric Power
Rate at which energy is used in the circuit