Resistance in Series and Parallel

Core B1.47
Calculating Resistance

Starter questions

1

State Ohms Law

2

What is the unit of resistance

3

Calculate 1/10 + 1/15 + 1/5

4

What is the mean average of this set of data: 2,1,3,3,2,2,2,1

5

What is the mode average of the data above?

KO 1

Prerequisite

knowledge

Memory in

science

Starter questions

1

V=IR

2

Ohms

3

0.36….

4

2.2 (2.18)

5

2

Prerequisite

knowledge

Memory in

science

Green pen your answers

Resistors in Series

In this presentation you will:

■ determine current, voltage and resistance for circuits with series

connected resistors
Next >

R1

R2

R3

V2

V3

V1

V

I

Introduction

Next >

In a series circuit, the
same current from the
battery flows through
each resistor.

Resistors are often
connected together in
series. It is possible to
predict these things:

■ voltage across resistors

■ total current flowing

■ total resistance of the circuit

V

R1
1 kΩ

R2
1 kΩ

I

Next >

Resistance of Resistors in Series

RT = R1 + R2 + R3

To calculate the total
resistance of resistors
connected in series, add
their values.

I

R1

R2

R3

I

Next >

Resistance of Resistors in Series

RT = R1 + R2 + R3

Here is an example
calculation of resistors
connected in series:

RT = 25 Ω + 75 Ω + 100 Ω

RT = 200 Ω

R1
25 Ω

R2
75 Ω

R3
100 Ω

Question 1

Next >

A) 15 kΩ

B) 22 kΩ

C) 47 kΩ

D) 69 kΩ

What single resistor could replace these two resistors connected in series?

22 kΩ

I

47 kΩ

What single resistor could replace these two resistors connected in series?

Question 1

Next >

RT = 69 kΩ

RT= R1+ R2

RT= 22 kΩ+ 47 kΩ

A) 15 kΩ

B) 22 kΩ

C) 47 kΩ

D) 69 kΩ

22 kΩ

I

47 kΩ

Core B1.47
Calculating Resistance

Core B1.47
Calculating Resistance

Multiple Choice

The circuit shown contains a battery, a 6.0 Ω resistor and two meters X and Y.

One meter records current and one meter records potential difference.

• meter X : 2.0 A

  meter Y : 12.0 V

• meter X : 2.0 V

  meter Y : 1.0 A

• meter X : 12.0 A

  meter Y : 2.0 V

• meter X : 12.0 V

  meter Y : 2.0 A

Multiple Choice

Which equation can be used to calculate the resistance R of a resistor?

• V = I / R

• I = V x R

• R = V x I

• V = I x R

Multiple Choice

A student uses a length of wire as a resistor. He makes a second resistor from the same material.

To be certain of making a second resistor of higher resistance, he should use a piece of wire that is:

• longer and thicker.

• longer and thinner.

• shorter and thicker.

• shorter and thinner.

Multiple Choice

How to you calculate the total resistance in a series circuit?

• R1 + R2+ R3

• R1 - R2 - R3

• 1/R1 + 1/R2 + 1/R3

• R1 = R2 = R3

Multiple Choice

The total resistance in this circuit is

• 100 ohms

• 450 ohms

• 400 ohms

• 30 ohms

Multiple Choice

Calculate the effective resistance of three resistors in series if they have the following values: 1.2 kΩ, 5.6 kΩ and 7.1 kΩ.

• $$6800\ \Omega$$
  

• $$12700\ \Omega$$

• $$13900\ \Omega$$

Next >

Three resistors are
connected in series
with a battery.

The supply voltage is
given by this equation:

In a series circuit, the
same current (I ) flows
through all components.

V = V1 + V2 + V3

V1 = I×R1

V2 = I×R2

V3 = I×R3

Voltage in a Series Circuit

I =V

RT

R1

R2

R3

V2

V3

V1

V

I

V2

V3

V1

V

Next >

Total resistance:

Voltage in a Series Circuit

RT = 200 Ω

I =V

RT

I =
10 V
200 Ω

I = 50 mA

R1
25 Ω

10 V

R2
75 Ω

R3
100 Ω

50 mA

Current:

Using equations,
calculate total resistance,
current and voltages.

RT = R1 + R2 + R3

Next >

V1 = I× R1

Voltage in a Series Circuit

I = 50 mA

V1 = 50 mA× 25 Ω

V1 = 1.25 V

V2 = I×R2

V2 = 50 mA× 75 Ω

V2 = 3.75 V

V3 = I× R3

V3 = 50 mA× 100 Ω

V3 = 5 V

RT = 200 Ω

Use the total resistance
and current to
calculate voltages.

R1
25 Ω

V
R2
75 Ω

R3
100 Ω

V2

V3

V1

50 mA

10 V

R1
25 Ω

V
R2
75 Ω

R3
100 Ω

Next >

Summary of values:

V = V1 + V2 + V3

Voltage in a Series Circuit

V1 = 1.25 V

V2 = 3.75 V

V3 = 5 V

I = 50 mA

RT = 200 Ω

V = 1.25 V + 3.75 V + 5 V

V = 10 V

Confirmation of total voltage:

V2

V3

V1

50 mA

10 V

Next >

What is the voltage across the 40 Ω resistor in this circuit?

Question 2

A)

4 V

B)

8 V

C) 12 V

D)

24 V

R1
20 Ω

V2

V3

V1

V

I

24 V

R2
40 Ω

R3
60 Ω

Next >

Question 2

RT= 20 Ω+ 40 Ω + 60 Ω

RT= 120 Ω

I =

24 V

120 Ω

I = 200 mA

V2 = I× R2

V2 = 200 mA× 40 Ω

V2 = 8 V

What is the voltage across the 40 Ω resistor in this circuit?

A)

4 V

B)

8 V

C) 12 V

D)

24 V

R1
20 Ω

V2

V3

V1

V

I

24 V

R2
40 Ω

R3
60 Ω

Multiple Choice

If V1 = 12V, V2 = 6V and V3 = 3V, what is V4?

• 4

• 3

• 12

• 6

Multiple Choice

If V1 = 9V and the resistance of each bulb is the same, what is V2, V3 and V4?

• 12

• 48

• 3

• 27

Multiple Choice

What is the missing voltage?

• 3

• 13

• 36

• 5

Next >

Equal value resistors
connected in series share
the supply voltage equally.

The voltage across each resistor
(VR) is given by the following
equation:

VR =
V

Number of resistors

Equal Value Resistors in Series

R1

V

R2

R3

R1

1.5 V

R2

R3

In this circuit the battery
has a voltage of 1.5 V.
Here is how to work out
the voltage across
each resistor.

The voltage across each resistor is 0.5 V.

Next >

VR =
V

Number of resistors

VR =
1.5 V

3

VR = 0.5 V

VR = VR1 = VR2=VR3

Equal Value Resistors in Series

0.5 V V

0.5 V V

0.5 V V

What is the voltage across each resistor in the circuit?

A)

R1 = 30 V, R2 = 15 V

B)

R1 = 15 V, R2 = 30 V

C)

R1 = 15 V, R2 = 15 V

D)

R1 = 30 V, R2 = 30 V

Question 3

Next >

R1
47 kΩ

R2
47 kΩ

30 V

Question 3

Next >

For equal value resistors, the supply voltage is shared equally.

What is the voltage across each resistor in the circuit?

R1
47 kΩ

R2
47 kΩ

30 V

A)

R1 = 30 V, R2 = 15 V

B)

R1 = 15 V, R2 = 30 V

C)

R1 = 15 V, R2 = 15 V

D)

R1 = 30 V, R2 = 30 V

Core B1.47
Calculating Resistance

Core B1.47
Calculating Resistance

Multiple Choice

How would the equivalent resistance be determined?

• 1 / Req = (1/5) + (1/8) + (1/3) Ω

• 120 Ω

• 1.5189873 Ω

• 1 / Req = (1/5) * (1/8) * (1/3) Ω

Multiple Choice

A 9.0 Ω resistor and another 9.0 Ω resistor are connected in parallel. What is their combined resistance?

• 0.5 Ω

• 2.0 Ω

• 4.5 Ω

• 9.0 Ω

Multiple Choice

Which one of the following resistors connected in parallel with a 24 Ω would give a total resistance of 8 Ω

• 16 Ω

• 12 Ω

• 8 Ω

• 6 Ω

You have 20 minutes to complete SLOP

1.

No questions for the first 5 minutes

2.

Golden silence 10 minutes

3.

Answer all teacher feedback with a green pen

4.

KO 1

Core B1.47
Calculating Resistance