Ohm

1
Ohms Law
Physics Dr. Robert MacKay
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Voltage (Volts) Electrical Pressure
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V
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Current (Amps)Charge Flow
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V

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Resistance, R (Ohms, ?)Impedence
I
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R Depends on Temperature Material of wire
Area of wire Length of wire
V

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Resistance, R (Ohms, ?)Impedence
Area
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Length
R Depends on Temperature Material of
wire Cros sectional Area Length
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Resistance and Resistivity
r resistivity Rresistance
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Ohms LawV I R
I
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V

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Exercise

• Find the electric voltage required to have 10
  Amps of current flow through a 2 ? resistor.
• Given I 10 A and R2 ?
• Wanted V
• Solution VI R
• V (10 A) (2 ?) 20 Volts

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Exercise

• Find the electric current flowing in a 10 ?
  resistor (light bulb) when connected to a 20 Volt
  battery.
• Given V 20 Vand R10 ?
• Wanted I
• Solution VI R or IV / R
• I (20 V) / (10 ?) 2 Amps

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Exercise

• When a 60 Volt battery is connected to a circuit
  4.0 amps of current flow from the battery. What
  is the circuits resistance.
• Given V 60 V and I4.0 Amps
• Wanted R
• Solution VI R or RV / I
• I (60 V) / (4.0 Amps) 15 ?

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DC
OFF
20M
200
2 M
200 k
V
AC
20
20 k
2
?
2 k
200 m
200
200 µ
2m
2
20 m
200 m
COM
.995
A
V-?
A
14
DC
OFF
20M
200
2 M
200 k
V
AC
20
20 k
2
?
2 k
200 m
200
200 µ
2m
2
20 m
200 m
COM
1 .
A
V-?
A
15
DC
OFF
20M
200
2 M
V
200 k
AC
20
20 k
2
?
2 k
200 m
200
200 µ
2m
2
20 m
200 m
COM
2.41
A
V-?
A
16
DC
OFF
20M
200
2 M
200 k
V
AC
20
20 k
2
?
2 k
200 m
200
200 µ
2m
2
20 m
200 m
COM
122.
A
V-?
A
17
DC
OFF
20M
200
2 M
200 k
V
AC
20
20 k
2
?
2 k
200 m
200
200 µ
2m
2
20 m
200 m
COM
0.082
A
V-?
A
18
DC
OFF
20M
200
2 M
200 k
V
AC
20
20 k
2
?
2 k
200 m
200
200 µ
2m
2
20 m
200 m
COM
65
A
V-?
A
19
DC
OFF
20M
200
2 M
200 k
V
AC
20
20 k
2
?
2 k
200 m
200
200 µ
2m
2
20 m
200 m
COM
65
A
V-?
A
20
DC
OFF
20M
200
2 M
200 k
V
AC
20
20 k
2
?
2 k
200 m
200
200 µ
2m
2
20 m
200 m
COM
156
A
V-?
A
21
DC
OFF
20M
200
2 M
200 k
V
AC
20
20 k
2
?
2 k
200 m
200
200 µ
2m
2
20 m
200 m
COM
156
A
V-?
A
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Electric Power (Watts)

• Power Current x Voltage
• 1 Watt Amp x Volt

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Curcuits
R10 ?
R
10 ?
I
P ?
I ?
A
V
20 V
P
V 20 V
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Curcuits
V I R or I V / R
R10 ?
R
10 ?
I
2.0 A
P ?
I ?
A
V
20 V
P
V 20 V
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Curcuits
V I R or I V / R
R10 ?
R
10 ?
I
2.0 Amps
P ?
I ?
A
V
20 V
40.0 Watts
P
V 20 V
P I V 2A(20V) 40W
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Curcuits
R?
R
I
P 60 W
I ?
A
V
120 V
60 W
P
V 120 V
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Curcuits
V I R
R?
R
I
P 60 W
I ?
A
V
120 V
60 W
P
V 120 V
P I V or IP/V60W/120V0.5A
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Curcuits
R?
R
I
0.50A
P 60 W
I ?
A
V
120 V
60 W
P
V 120 V
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Curcuits
R?
R
I
0.50A
P 60 W
I ?
A
V
120 V
60 W
P
V 120 V
RV/I120V/0.5A240W
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Curcuits
R?
R
240W
I
0.50A
P 60 W
I ?
A
V
120 V
60 W
P
V 120 V
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Series Curcuits
R110 ?
R210 ?
Req 20 ?
A
I ?
I1 I2 I V/Req
V 20 V
Req R1R2
V1V220V
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Series Curcuits
R10 ?
R10 ?
Req 20 ?
A
I ?
I1 I2 I V/Req 1.0 A
V 20 V
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Parallel Curcuits
V1V2V20V
R10 ?
I1
I1
I1 V/R120V/10W 2A I2 V/R2 2A
I2
R10 ?
A
I
I1 I2 I 4A

I
ReqV/I20V/4A 5 ?
V 20 V
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Series Curcuits
R8 ?
R2 ?
Req 10 ?
A
I ?
I1 I2 I V/R 2.0 A
V 20 V