ch. 34 electric current. movement or “flow” of charge occurs when there is a difference in...
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Ch. 34
Electric Current
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Electric Current• Movement or “flow” of charge
• Occurs when there is a difference in voltage between the ends of a conductor
• Electrons carry charges through solid circuits
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Electric Current (I)
Current = charge I = q
time t
• Measured in amperes (amps or A)
Example: Calculate the current where 20 coulombs of charge pass a point in 8 seconds.
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Electric Current (I)
Current = charge I = q
time t
• Measured in amperes (amps or A)
Example: Calculate the current where 20 coulombs of charge pass a point in 8 seconds. 20 C / 8 s = 2.5 amps
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Voltage Sources• Provide a potential difference so that
charges are able to flow– Examples: Dry Cells or Wet Cells– Energy from a chemical reaction is
converted to electrical energy
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Voltage (V)
• The potential energy per coulomb of charge available to electrons moving between terminals
• Typical voltage in a home is 120 V• 120 Joules of energy are supplied to each
coulomb of charge that flows in a circuit!!!
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Remember that….
Charge flows because of an applied voltage across the circuit
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Electric Resistance (R)
Measured in ohms, Ω
Depends on:• Conductivity of material• Diameter of wire
– Thick wires have less resistance than thin wires
• Length of wire– Longer wires have more resistance than
shorter wires
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Ohm’s Law
I = V/RCurrent = Voltage / Resistance
Units: amps = volts / ohms
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I = V/RA 120 ohm heating element is powered by
a 10 volt battery. What is the current?
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I = V/RA 120 ohm heating element is powered by
a 10 volt battery. What is the current?
10 V / 120 ohm = 0.083 amps
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Direct Current (DC)• Charge always flow in one direction
– Ex. Batteries
Alternating Current (AC)• Charge alternates directions as it flows
– Ex. Our outlets
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Since our outlets produce AC current, but many appliances use
DC, what can we do…..Convert AC to DC
• Diode: a converter that only allows electrons to flow in one direction
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Electric Power
• The rate at which electrical energy is converted into another form
• Power = current x voltage
• P = IV
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Ch. 34 Practice
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Ch. 35 Electric Circuits
• Series Circuits
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For Problem Solving in Series
• Resistances are ADDED
• R1 + R2 + R3 = R total
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The resistance of one lamp is 10 ohms. What is the total resistance for the circuit shown?
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The resistance of one lamp is 10 ohms. What is the total resistance for the circuit shown?
R total = 10 + 10 + 10 = 30 ohms
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The resistance of one lamp is 10 ohms. What is the total resistance for the circuit shown?
R total = 10 + 10 + 10 = 30 ohms
If the attached voltage source is 10 V, what is the current in the circuit?
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The resistance of one lamp is 10 ohms. What is the total resistance for the circuit shown?
R total = 10 + 10 + 10 = 30 ohms
If the attached voltage source is 10 V, what is the current in the circuit?
I = V/R
I = 10 V / 30 ohms
I = 0.33 amps
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• Parallel Circuits
1 = 1 + 1 + 1
Rtotal R1 R2 R3
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• Parallel Circuits
The resistance of one lamp is 10 ohms. What is the total resistance for the circuit shown?
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• Parallel Circuits
The resistance of one lamp is 10 ohms. What is the total resistance for the circuit shown?
1/10 + 1/10 + 1/10 = 1 / Rtotal
0.3 = 1 / Rtotal
Rtotal = 1/0.3 = 3.33
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• Parallel Circuits
The resistance of one lamp is 10 ohms. What is the total resistance for the circuit shown?
Rtotal = 1/0.3 = 3.33
If the attached voltage source is 10 V, what is the current in the circuit?
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• Parallel Circuits
The resistance of one lamp is 10 ohms. What is the total resistance for the circuit shown?
Rtotal = 1/0.3 = 3.33
If the attached voltage source is 10 V, what is the current in the circuit?
I = V/R
I = 10 V / 3.33 ohms
I = 3 amps
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Ch. 35 Lab and Practice