Electric CircuitsElectric Circuits

• Electric charges always move from high-voltage to low-voltage.

• Travels from negative to positive[http://www.energyquest.ca.gov/story/images/chap04_circuit.gif]

Click Here for an Interactive Example

Electric CircuitsElectric Circuits

• Voltage difference “forces” charges along a conductor and is measured in volts (V)

• Also called potential difference

[http://www.speedysigns.com/images/osha/large/DANGER54.gif]

[http://www.bcae1.com/images/gifs/voltage1.gif]

Water Tower analogy for Voltage

phttp://www.cartoonstock.com/newscartoons/cartoonists/ksm/lowres/ksmn1044l.jpg[

Common Error About Voltage…

Electric CircuitsElectric Circuits

• Electric Current is the flow of charges (electrons) and is measured in amperes (A).

[http://www.heirloomradio.com/images/coulomb.jpg]

[http://www.smud.org/safety/world/hurt/media/current_chart.gif]

Electric Circuits• Resistance is the

tendency for materials to oppose the flow of electrons.

• Electrical energy is commonly changed into heat, light, or motion.

[http://www.energyquest.ca.gov/story/images/chap04_circuit.gif]

Electric CircuitsElectric Circuits

• Resistance is measured in ohms (Ω).

Click here for a video example of resistance.

phttp://www.cartoonstock.com/newscartoons/cartoonists/ksm/lowres/ksmn1044l.jpg]

Ohm’s LawOhm’s Law

• As the resistance in the circuit increases, the current (number of charges) decreases.

• V = I R

Click Here for an Interactive Example

Ohm’s LawOhm’s Law

• Example:

• A circuit has a resistance of 0.5 Ω and has a current of 3.0 A. What size battery in volts is needed?

• V = (3.0 A) x (0.5 Ω)

• V = 1.5 V

Ohm’s LawOhm’s Law

• Example:

• A 9-volt battery is used in a circuit with a resistance of 1.5 Ω. What current is needed?

• (9 V) = I (1.5 Ω)(1.5 Ω) (1.5 Ω)

I = 6.0 A

Circuit DiagramsCircuit Diagrams

• A 2-dimensional representation of an electrical circuit.

[http://www.ise5-14.org.uk/Prim3/New_Guidelines/Newsletters/9/IMGS/bulb.gif]

Some diagram symbols include…

Open Switch

Light Bulb

Voltmeter

Ammeter

or

Series CircuitsSeries Circuits

• The current only has one possible circuit to pass through.

[http://iss.cet.edu/electricity/pages/images/B/b13_2.jpg]

[http://www.danieltrimpey.com/learn/electronics/images/series.GIF]

1

2

3

...VV VVoltage 321total ...IIICurrent 321total ...RRRResistance 321total

Parallel CircuitsParallel Circuits

• There are two or more branches on each circuit for current to move through.

[http://iss.cet.edu/electricity/pages/images/B/b13_3.jpg]

1 2 3

...VV VVoltage 321total ...IIICurrent 321total

...R1

R1

R1

1Resistance

321

total

[http://www.danieltrimpey.com/learn/electronics/images/series.GIF]

Circuit Protection DevicesCircuit Protection Devices

• If too much current flows through a circuit, a safety device shuts off the current in order to prevent it from overheating.

Circuit Protection DevicesCircuit Protection Devices

• Fuses

• A small piece of metal that will melt if too much current passes through it.

[http://hollyfuse.en.alibaba.com/product/50020315/50104654/5_phi__Fuses/50T_Fuses/showimg.html]

May only be used once, then must be replaced.

Circuit Protection DevicesCircuit Protection Devices

• Circuit Breaker• A piece of metal

bends if too much current passes through, and it turns off the switch to the circuit.

• Just need to reset the switch to use again

[http://www3.sympatico.ca/mmatkiwsky/reng/images/Trailer/breakers.JPG]