Transcript Electric Current

Electric Circuits
[http://www.energyquest.ca.gov/story/images/chap04_circuit.gif]
• Electric charges
always move from
high-voltage to
low-voltage.
• Travels from
negative to
positive
Click Here for an Interactive Example
Electric 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]
Water Tower analogy for Voltage
[http://www.bcae1.com/images/gifs/voltage1.gif]
Common Error About Voltage…
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Electric 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 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 Law
• As the resistance in the circuit
increases, the current (number of
charges) decreases.
• V=IR
Click Here for an Interactive
Example
Ohm’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 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)
I = 6.0 A
(1.5 Ω) (1.5 Ω)
Circuit 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
or
Light Bulb
Voltmeter
Ammeter
Series 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]
3
2
1
Voltagetotal  V1  V2  V3...
Currenttotal  I1  I2  I3...
Resistancetotal  R1  R 2  R 3...
Parallel 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]
[http://www.danieltrimpey.com/learn/electronics/images/series.GIF]
1
2
3
Voltagetotal  V1  V2  V3...
Currenttotal  I1  I2  I3...
Resistancetotal
1

1
1
1


...
R1 R 2 R 3
Circuit 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 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 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]