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]