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Speed of Light with Peeps
Ohm’s Law Worksheet
1.
2.
3.
4.
5A
6A
12 A
Decreases => current increases;
Increases=> current decreases
*Inverse Relationship
5. 10 V
6. 20 V
7. Decreases => voltage decreases
Increases=> current decreases
*Direct Relationship
8. 10 Ω
9. 120 Ω
10. Decreases=> voltage decreases
Increases => voltage increases
* Direct Relationship
11. 24 V
12. 2 A
13. 24 Ω
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Circuits
Series Calculations
Simple circuits
 When the switch is closed, the lamp lights up. This is because there is
a continuous path of metal for the electric current to flow around.
 If there were any breaks in the circuit, the current could not flow.
Circuit Diagram
+
_
 Scientists usually draw
electric circuits using
symbols;
 Electrons flow in a closed
circuit opposite the indicated
current direction!(repelled by
negative terminal)
Series Circuit
Series Circuit
 One path in and one path out…..
 Current is the same everywhere
 I1 = I2 = I3 = I4 = In
_
+
 Voltage is shared between the
components
2A
3V
 V = V1 + V2 + V3 + V4 + Vn
 V = IR
 V = I1R1 + I1R1 + I1R1 + InRn
 & I1 = I2 = I3 = I4 = In thus…
2A
1.5V
1.5V
2A
.75 Ω
 Resistance is shared between the
components like voltage
.75 Ω
 R = R1 + R2 + R3 + R4 + Rn
Series Circuit Example 1:
 In the circuit below:
 R1=4Ω, R2=2Ω, and R3=6Ω.
 Current = .5A
 Voltage at the source?
 Current is the same I1 = I2 = I3 = I4 = In
 Voltage is shared
 V = V1 + V2 + V3 + V4 + Vn
 Resistance is shared
 R = R1 + R2 + R3 + R4 + Rn
V
R1
R2
R3
Total
I
R
Series Circuit Example 1:
 In the circuit below:
 R1=4Ω, R2=2Ω, and R3=6Ω.
 Current = .5A
 Voltage at the source?
 Current is the same I1 = I2 = I3 = I4 = In
 Voltage is shared
 V = V1 + V2 + V3 + V4 + Vn
 Resistance is shared
 R = R1 + R2 + R3 + R4 + Rn
V
R1
R2
R3
Total
I
R
Series Circuit Example 2:
• In the circuit below:
• R1=60Ω, R2=100Ω, and R3=150Ω.
• Current = 1.5A
• Voltage at the source?
• Current is the same I1 = I2 = I3 = I4 = In
• Voltage is shared
• V = V1 + V2 + V3 + V4 + Vn
• Resistance is shared
• R = R 1 + R 2 + R 3 + R 4 + Rn
V
R1
R2
R3
Total
I
R
Series Circuit Example 2:
• In the circuit below:
• R1=60Ω, R2=100Ω, and R3=150Ω.
• Current = 1.5A
• Voltage at the source?
• Current is the same I1 = I2 = I3 = I4 = In
• Voltage is shared
• V = V1 + V2 + V3 + V4 + Vn
• Resistance is shared
• R = R 1 + R 2 + R 3 + R 4 + Rn
V
R1
R2
R3
Total
I
R
Series Circuit Example 3:
• In this circuit :
• R1=100Ω, R2=300Ω, and R3=50Ω.
• Current = Voltage =9V
• Current is the same I1 = I2 = I3 = I4 = In
• Voltage is shared
• V = V1 + V2 + V3 + V4 + Vn
• Resistance is shared
• R = R 1 + R 2 + R 3 + R 4 + Rn
V
R1
R2
R3
Total
I
R
Series Circuit Example 3:
• In this circuit :
• R1=100Ω, R2=300Ω, and R3=50Ω.
• Current = Voltage =9V
• Current is the same I1 = I2 = I3 = I4 = In
• Voltage is shared
• V = V1 + V2 + V3 + V4 + Vn
• Resistance is shared
• R = R 1 + R 2 + R 3 + R 4 + Rn
V
R1
R2
R3
Total
I
R
Circuits
Parallel Calculations
Kirchoff’s
st
1
Law (KVL)
 Voltages around a closed path in a
circuit must equal 0.
∑V=∆V
V = V1 = V2 = V3 = V4 = Vn
Kirchoff’s
nd
2
Law (KCL)
2A
4A
 Total current (IT) entering a junction must
equal the total current leaving the
junction.
 A junction is any place in a circuit
where more than two paths come
together.
2A
7A
3A
4A
5A
3A
2A
3A
4A
2A
3A
Parallel Circuit
 2 or more paths to flow
 Current is shared between the
components
 IT = I1 + I2 + I3 + I4 + In
 Voltage is the same everywhere
 V = V1 = V2 = V3 = V4 = Vn
 Resistance is calculated by using the
formula
 R (t)otal = 1/Rt = 1/R1 + 1/R2 + 1/R3 +...
 If 1 path is broken, the current will
continue to flow in all other paths
Parallel Circuit Example 1:
 In this circuit :
 R1=4Ω, R2=2Ω, and R3=6Ω.
 Current = ?
 Voltage = 6V
 Current is shared (I = V/R)
 In = I1 + I2 + I3
V
 Voltage is same
 V = V1 = V2 = V3
 Resistance is 1/R + …..
 R = 1/R1 + 1/R2 + 1/R3
R1
R2
R3
Total
I
R
1/R
Parallel Circuit Example 1:
 In this circuit :
 R1=4Ω, R2=2Ω, and R3=6Ω.
 Current = ?
 Voltage = 6V
 Voltage is same
 V = V1 = V2 = V3
 Resistance is 1/R + …..
• RT = 1/R = 1/4 + 1/2 + 1/6
• = 1/(.25 +.50 + .17)
• = 1/.92 = 1.09
 Current is shared * (V=IR=> I =V/R)
 In = V/R
= 6V / 1.09
= 5.5
V
I
R
1/R
R1
6
1.5
4
1/4 = 3/12
R2
6
3
2
½ = 6/12
R3
6
1
6
1/6 = 2/12
Total
6
5.5
1.09
11/12 = .92
Parallel Circuit Example 2:
 In this circuit :
 R1=50Ω, R2=75Ω.
 Current = ?
 Voltage = 6V
 Current is shared (I = V/R)
 In = I1 + I2 + I3
V
 Voltage is same
 V = V1 = V2 = V3
 Resistance is 1/R + …..
 R = 1/R1 + 1/R2 + 1/R3
R1
R2
Total
I
R
1/R
Parallel Circuit Example 2:
 In this circuit :
 R1=50Ω, R2=75Ω
 Current = ?
 Voltage = 6V
 Voltage is same
 V = V1 = V2 = V3
 Resistance is 1/R + …..
• RT = 1/R = 1/50 + 1/75
• = 1/(.02 + .013)
• = 1/.033 = .198 (~.2)
 Current is shared * (V=IR=> I =V/R)
 IT = VT/RT
= 6V / 30.3
= 1.28 A
V
I
R
1/R
R1
6
6/50 = .12
50
1/50 = 15/75 = .02
R2
6
6/75 = .08
75
1/75 = 1/75 = .013
Total
6
.198 (~.2)
30.3
16/75 = .033
Parallel Circuit Example 3:
 In this circuit :
 R1=4Ω, R2=4Ω, and R3=2Ω.
 Current = ?
 Voltage = 12V
 Current is shared (I = V/R)
 In = I1 + I2 + I3
V
 Voltage is same
 V = V1 = V2 = V3
 Resistance is 1/R + …..
 R = 1/R1 + 1/R2 + 1/R3
R1
R2
R3
Total
I
R
1/R
Parallel Circuit Example 3:
 In this circuit :
 R1=4Ω, R2=4Ω, and R3=2Ω.
 Current = ?
 Voltage = 6V
 Current is shared (I = V/R)
 In = I1 + I2 + I3
 Voltage is same
 V = V1 = V2 = V3
 Resistance is 1/R + …..
 R = 1/R1 + 1/R2 + 1/R3
V
I
R
1/R
R1
6
1.5
4
1/4 = 1/4 = .25
R2
6
1.5
4
1/4 = 1/4 = .25
R3
6
3
2
1/2 = 2/4 = .5
Total
6
6
1/1 =1
1