Transformers and their Equations

Question 1

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Q1 → What is a transformer and what does it do?
A transformer is a device that changes the potential difference (voltage) of an alternating current. It is used to increase or decrease the potential difference in electrical circuits.

Q2 → What is the purpose of transformers in energy transmission?
Transformers are used to change the potential difference so that energy can be transmitted efficiently over long distances.

Q3 → What type of current do transformers require to work?
Transformers only work with alternating current (AC) because they rely on a changing current to produce a changing magnetic field.

Q4 → Why can transformers not work with direct current (DC)?
Transformers cannot work with direct current because DC does not change, so it does not produce a changing magnetic field, which is required to induce a potential difference in the secondary coil.

Q5 → What are the two main types of transformers?
The two main types of transformers are step-up transformers and step-down transformers.

Q6 → What does a step-up transformer do?
A step-up transformer increases the potential difference (voltage) of an alternating current.

Q7 → What happens to current in a step-up transformer?
In a step-up transformer, the current decreases when the potential difference increases.

Q8 → What does a step-down transformer do?
A step-down transformer decreases the potential difference (voltage) of an alternating current.

Q9 → What happens to current in a step-down transformer?
In a step-down transformer, the current increases when the potential difference decreases.

Q10 → What is the basic structure of a transformer?
A transformer consists of two coils of wire called the primary coil and the secondary coil, which are wound around an iron core.

Q11 → What is the primary coil in a transformer?
The primary coil is the coil connected to the input alternating current supply.

Q12 → What is the secondary coil in a transformer?
The secondary coil is the coil connected to the output circuit where the transformed potential difference is produced.

Q13 → Are the primary and secondary coils electrically connected?
No, the primary and secondary coils are not electrically connected; instead, they are linked by a magnetic field through the iron core.

Q14 → Why is an iron core used in a transformer?
Iron is used because it is easily magnetised, allowing it to efficiently carry and strengthen the magnetic field between the coils.

Q15 → How does a transformer work step-by-step?

A primary voltage drives an alternating current through the primary coil.
The current in the primary coil produces a magnetic field.
This magnetic field changes as the current changes.
The iron core strengthens the magnetic field.
The changing magnetic field is transferred through the iron core to the secondary coil.
This changing magnetic field induces a changing potential difference in the secondary coil.
The induced potential difference produces an alternating current in the external circuit if the secondary coil is part of a complete circuit.

Q16 → What happens to the iron core when an alternating potential difference is applied?
The iron core magnetises and demagnetises rapidly, creating a changing magnetic field.

Q17 → What causes a potential difference to be induced in the secondary coil?
A changing magnetic field in the iron core induces a potential difference in the secondary coil.

Q18 → What condition is needed for current to flow in the secondary coil?
The secondary coil must be part of a complete circuit for the induced potential difference to produce a current.

Q19 → How does the number of turns affect a step-up transformer?
In a step-up transformer, the secondary coil has more turns than the primary coil.

Q20 → How does the number of turns affect a step-down transformer?
In a step-down transformer, the secondary coil has fewer turns than the primary coil, meaning the primary coil has more turns.

Q21 → What is the relationship between potential difference and number of turns in a transformer?
The ratio of the potential differences across the coils is equal to the ratio of the number of turns on the coils.

Q22 → What is the transformer equation relating potential difference and turns?

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Q23 → What do the symbols in the transformer equation mean?
Vp is the potential difference across the primary coil in volts (V).
Vs is the potential difference across the secondary coil in volts (V).
Np is the number of turns on the primary coil.
Ns is the number of turns on the secondary coil.

Q24 → How can the transformer equation be rearranged?
The equation can also be written as Vs / Vp = Ns / Np, and it can be used either way up depending on which value is unknown.

Q25 → What is true about potential differences in step-up and step-down transformers?
In a step-up transformer, Vs > Vp.
In a step-down transformer, Vs < Vp.

Q26 → What is the equation for electrical power?

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P=VI

Q27 → What do the symbols in the power equation represent?
P is power measured in watts (W).
V is potential difference measured in volts (V).
I is current measured in amperes (A), also called amps.

Q28 → What is the power relationship in an ideal transformer?
If a transformer is 100% efficient, the power input to the primary coil is equal to the power output from the secondary coil.

Q29 → What is the transformer power equation for an ideal transformer?

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I
s
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Q30 → What do the terms in the transformer power equation represent?
VpIp represents the input power at the primary coil.
VsIs represents the output power at the secondary coil.

Q31 → How efficient are transformers in reality?
Transformers are almost 100% efficient, meaning most of the input power is transferred to the output.

Q32 → What is the National Grid?
The National Grid is the network that connects power stations across the country to ensure that electricity is supplied everywhere.

Q33 → Why do high currents cause energy loss in transmission cables?
Higher currents cause more energy to be transferred to the surroundings as heat, increasing energy losses.

Q34 → How does increasing potential difference reduce energy loss?
Increasing the potential difference reduces the current for the same power, which reduces heating losses in the cables.

Q35 → How are step-up transformers used in the National Grid?
Step-up transformers increase the voltage from power stations to very high values (thousands of volts), which reduces the current in transmission cables.

Q36 → Why is reducing current important in power transmission?
Reducing current decreases the amount of energy lost as heat in the wires, making transmission more efficient.

Q37 → How are step-down transformers used in the National Grid?
Step-down transformers reduce the high transmission voltage to lower, safer levels for use in homes and factories.

Q38 → Why must the voltage be reduced before reaching homes?
The voltage must be reduced to safer levels because very high voltages used in transmission would be dangerous for domestic and industrial use.

Answer 1

Source 1: Transformers:
TRANSFORMERS are used to change the POTENTIAL DIFFERENCE for efficient energy transmission over long distances.

There are TWO types of TRANSFORMERS:

1. STEP-UP TRANSFORMERS:
   These INCREASE the POTENTIAL DIFFERENCE and DECREASE the CURRENT.
2. STEP-DOWN TRANSFORMERS:
   These decrease the POTENTIAL DIFFERENCE and INCREASE the CURRENT.

Structure of a Transformer:
A transformer consists of a PRIMARY COIL and a SECONDARY COIL wound on an IRON CORE.

IRON is used as it is EASILY MAGNETISED. The incoming ALTERNATING current flows through the PRIMARY COIL and creates a CHANGING MAGNETIC FIELD in the IRON CORE.

The SECONDARY COIL also experiences the CHANGING MAGNETIC FIELD in the IRON CORE, which leads to a POTENTIAL DIFFERENCE being INDUCED.

A STEP UP transformer has MORE turns in its SECONDARY coil than its PRIMARY coil.

A STEP DOWN transformer has LESS turns in its SECONDARY coil than its PRIMARY coil.

Transformer Equations:
If transformers were 100% EFFICIENT, the POWER transferred by a transformer is almost equal in the primary and secondary coils. By knowing this we can derive the following equation:

                                                                                                                                                       Potential Difference across Primary Coil (V) × Current in Primary Coil (A) = Potential Difference across Secondary Coil (V) × Current in Secondary Coil (A)       [short-hand form: VₚIₚ = VₛIₛ]

                                                                                                                                                       Where:  VP and IP are the POTENTIAL DIFFERENCE and CURRENT in the PRIMARY coil. VS and IS are the POTENTIAL DIFFERENCE and CURRENT in the SECONDARY coil.

Another equation involves POTENTIAL DIFFERENCE and the NUMBER OF TURNS in the coils:

Potential Difference across Primary Coil (V) / Potential Difference across Secondary Coil (V) = Number of Turns in Primary Coil / Number of Turns in Secondary Coil [short-hand form: Vₚ / Vₛ = Nₚ / Nₛ] //////////// Source 2: Transformers:

A transformer is a device that can change the potential difference or voltage of an alternating current:
- a step-up transformer increases the voltage
- a step-down transformer reduces the voltage

Design and use of transformers:

A basic transformer is made from two coils of wire, a primary coil from the alternating current (ac) input and a secondary coil leading to the ac output. The coils are not electrically connected. Instead, they are wound around an iron core. This is easily magnetised and can carry magnetic fields from the
primary coil to the secondary coil. ||| When a transformer is working:

1. a primary voltage drives an alternating current through the primary coil
2. the primary coil current produces a magnetic field, which changes as the current changes
3. the iron core increases the strength of the magnetic field
4. the changing magnetic field induces a changing potential difference in the secondary coil
5. the induced potential difference produces an alternating current in the external circuit

Remember that transformers can only work with alternating current. ||| Potential Difference: The ratio of potential differences on the transformer coils matches the ratio of the numbers of turns on the coils.

This equation can be used to calculate what the output might be from a particular transformer, or to work out how to design a transformer to make a particular voltage change:

Potential Difference across Primary Coil (V) / Potential Difference across Secondary Coil (V) = Number of Turns in Primary Coil / Number of Turns in Secondary Coil [short-hand form: Vₚ / Vₛ = Nₚ / Nₛ]

This is when:

. Vp is the potential difference in the primary (input) coil in volts (V)
. Vs is the potential difference in the secondary (output) coil in volts (V)
. np is the number of turns on the primary coil
. ns is the number of turn on the secondary coil

In a step-up transformer, Vs > Vp. In a step-down transformer, Vs < Vp. ||| Electrical Power:
To calculate electrical power, use the equation:

power = potential difference x current

P =VI

This is when:
- power (P) is measured in watts (W)
- potential difference (V) is measured in volts (V)
- current (/) is measured in amperes - also referred to as amps (A)

Assuming that a transformer is 100 percent efficient, the following equation can be used to calculate the power output from the transformer:

potential difference across primary coil x current in primary coil = potential difference across secondary coil x current in secondary coil [short-hand form: VₚIₚ = VₛIₛ] ||| Power Transmission:
The National Grid (the network that connects all of the power stations in the country to make sure that everywhere has access to electricity) carries electricity around Britain. The higher the current in a cable, the greater the energy transferred to the surroundings by heating. This means that high currents waste more energy than low currents.

To reduce energy transfers to the environment, the National Grid uses step-up transformers to increase the voltage from power stations to thousands of volts, which lowers the current in the transmission cables. Step-down transformers are then used to decrease the voltage from the transmission cables, so it is safer to distribute to homes and factories. //////////// Source 3: Transformers:
Transformers only work with an alternating current.
Transformers Change the pd — but Only for Alternating Current:
Transformers change the size of the potential difference of an alternating current.
They all have two coils of wire, the primary and the secondary, joined with an iron core.
When an alternating pd is applied across the primary coil, the iron core magnetises and demagnetises quickly. This changing magnetic field induces an alternating pd in the secondary coil.
If the second coil is part of a complete circuit, this causes a current to be induced.
The ratio between the primary and secondary potential differences is the same as the ratio between the number of turns on the primary and secondary coils. Iron is used because it’s easily magnetised.

STEP-UP TRANSFORMERS step the potential difference up (i.e. increase it). They have more turns on the secondary coil than the primary coil.
STEP-DOWN TRANSFORMERS step the potential difference down (i.e. decrease it). They have more turns on the primary coil than the secondary.
||| The Transformer Equation — Use it Either Way Up:
As long as you know the input pd and the number of turns on each coil, you can calculate the output pd from a transformer using the transformer equation:

(Input potential difference (V)) / (Output potential difference (V)) = Vp / Vs = np / ns = (Number of turns on primary coil) / (Number of turns on secondary coil)
For a step-up transformer, Vs > Vp and for a step-down transformer, Vs < Vp.
This equation can be used either way up, so Vs / Vp = ns / np works just as well. There’s less rearranging to do if you put whatever you’re trying to find (the unknown) on the top.
Transformers are almost 100% efficient. If you assume that they are, then the input power is equal to the output power. Using P = VI, you can write the following equation:

Vs Is = Vp Ip
(Pd across secondary coil (V) x Current through secondary coil (A) = Pd across primary coil (V) x Current through primary coil (A))

Vs Is is the power output at the secondary coil.
Vp Ip is the power input at the primary coil.
You need to be able to relate both of these equations to power transmission in the national grid, to explain why and how the national grid transmits at very high pds.
You’ve seen that a low current means that less energy is wasted heating the wires and the surroundings, making the national grid an efficient way of transmitting power.

Question 2

Q1 → What is a transformer and what does it do?

Question 3

A transformer is a device that changes the potential difference (voltage) of an alternating current. It is used to increase or decrease the potential difference in electrical circuits.

Question 4

Q2 → What is the purpose of transformers in energy transmission?

Question 5

Transformers are used to change the potential difference so that energy can be transmitted efficiently over long distances.

Question 6

Q3 → What type of current do transformers require to work?

Question 7

Transformers only work with alternating current (AC) because they rely on a changing current to produce a changing magnetic field.

Question 8

Q4 → Why can transformers not work with direct current (DC)?

Question 9

Transformers cannot work with direct current because DC does not change

Answer 9

so it does not produce a changing magnetic field

Question 10

Q5 → What are the two main types of transformers?

Question 11

The two main types of transformers are step-up transformers and step-down transformers.

Question 12

Q6 → What does a step-up transformer do?

Question 13

A step-up transformer increases the potential difference (voltage) of an alternating current.

Question 14

Q7 → What happens to current in a step-up transformer?

Question 15

In a step-up transformer

Answer 15

the current decreases when the potential difference increases.

Question 16

Q8 → What does a step-down transformer do?

Question 17

A step-down transformer decreases the potential difference (voltage) of an alternating current.

Question 18

Q9 → What happens to current in a step-down transformer?

Question 19

In a step-down transformer

Answer 19

the current increases when the potential difference decreases.

Question 20

Q10 → What is the basic structure of a transformer?

Question 21

A transformer consists of two coils of wire called the primary coil and the secondary coil

Answer 21

which are wound around an iron core.

Question 22

Q11 → What is the primary coil in a transformer?

Question 23

The primary coil is the coil connected to the input alternating current supply.

Question 24

Q12 → What is the secondary coil in a transformer?

Question 25

The secondary coil is the coil connected to the output circuit where the transformed potential difference is produced.

Question 26

Q13 → Are the primary and secondary coils electrically connected?

Question 27

No

Answer 27

the primary and secondary coils are not electrically connected; instead

Question 28

Q14 → Why is an iron core used in a transformer?

Question 29

Iron is used because it is easily magnetised

Answer 29

allowing it to efficiently carry and strengthen the magnetic field between the coils.

Question 30

Q15 → How does a transformer work step-by-step?

Question 31

A primary voltage drives an alternating current through the primary coil.

Question 32

The current in the primary coil produces a magnetic field.

Question 33

This magnetic field changes as the current changes.

Question 34

The iron core strengthens the magnetic field.

Question 35

The changing magnetic field is transferred through the iron core to the secondary coil.

Question 36

This changing magnetic field induces a changing potential difference in the secondary coil.

Question 37

The induced potential difference produces an alternating current in the external circuit if the secondary coil is part of a complete circuit.

Question 38

Q16 → What happens to the iron core when an alternating potential difference is applied?

Question 39

The iron core magnetises and demagnetises rapidly

Answer 39

creating a changing magnetic field.

Question 40

Q17 → What causes a potential difference to be induced in the secondary coil?

Question 41

A changing magnetic field in the iron core induces a potential difference in the secondary coil.

Question 42

Q18 → What condition is needed for current to flow in the secondary coil?

Question 43

The secondary coil must be part of a complete circuit for the induced potential difference to produce a current.

Question 44

Q19 → How does the number of turns affect a step-up transformer?

Question 45

In a step-up transformer

Answer 45

the secondary coil has more turns than the primary coil.

Question 46

Q20 → How does the number of turns affect a step-down transformer?

Question 47

In a step-down transformer

Answer 47

the secondary coil has fewer turns than the primary coil

Question 48

Q21 → What is the relationship between potential difference and number of turns in a transformer?

Question 49

The ratio of the potential differences across the coils is equal to the ratio of the number of turns on the coils.

Question 50

Q22 → What is the transformer equation relating potential difference and turns?

Question 51

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Question 52

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Question 53

𝑉

Question 54

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Question 55

=

Question 56

𝑁

Question 57

𝑝

Question 58

𝑁

Question 59

𝑠

Question 60

V

Question 61

s

Question 62

​

Question 63

V

Question 64

p

Question 65

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Question 66

​

Question 67

=

Question 68

N

Question 69

s

Question 70

​

Question 71

N

Question 72

p

Question 73

​

Question 74

​

Question 75

Q23 → What do the symbols in the transformer equation mean?

Question 76

Vp is the potential difference across the primary coil in volts (V).

Question 77

Vs is the potential difference across the secondary coil in volts (V).

Question 78

Np is the number of turns on the primary coil.

Question 79

Ns is the number of turns on the secondary coil.

Question 80

Q24 → How can the transformer equation be rearranged?

Question 81

The equation can also be written as Vs / Vp = Ns / Np

Answer 81

and it can be used either way up depending on which value is unknown.

Question 82

Q25 → What is true about potential differences in step-up and step-down transformers?

Question 83

In a step-up transformer

Answer 83

Vs > Vp.

Question 84

In a step-down transformer

Answer 84

Vs < Vp.

Question 85

Q26 → What is the equation for electrical power?

Question 86

𝑃

Question 87

=

Question 88

𝑉

Question 89

𝐼

Question 90

P=VI

Question 91

Q27 → What do the symbols in the power equation represent?

Question 92

P is power measured in watts (W).

Question 93

V is potential difference measured in volts (V).

Question 94

I is current measured in amperes (A)

Answer 94

also called amps.

Question 95

Q28 → What is the power relationship in an ideal transformer?

Question 96

If a transformer is 100% efficient

Answer 96

the power input to the primary coil is equal to the power output from the secondary coil.

Question 97

Q29 → What is the transformer power equation for an ideal transformer?

Question 98

𝑉

Question 99

𝑝

Question 100

𝐼

Question 101

𝑝

Question 102

=

Question 103

𝑉

Question 104

𝑠

Question 105

𝐼

Question 106

𝑠

Question 107

V

Question 108

p

Question 109

​

Question 110

I

Question 111

p

Question 112

​

Question 113

=V

Question 114

s

Question 115

​

Question 116

I

Question 117

s

Question 118

​

Question 119

Q30 → What do the terms in the transformer power equation represent?

Question 120

VpIp represents the input power at the primary coil.

Question 121

VsIs represents the output power at the secondary coil.

Question 122

Q31 → How efficient are transformers in reality?

Question 123

Transformers are almost 100% efficient

Answer 123

meaning most of the input power is transferred to the output.

Question 124

Q32 → What is the National Grid?

Question 125

The National Grid is the network that connects power stations across the country to ensure that electricity is supplied everywhere.

Question 126

Q33 → Why do high currents cause energy loss in transmission cables?

Question 127

Higher currents cause more energy to be transferred to the surroundings as heat

Answer 127

increasing energy losses.

Question 128

Q34 → How does increasing potential difference reduce energy loss?

Question 129

Increasing the potential difference reduces the current for the same power

Answer 129

which reduces heating losses in the cables.

Question 130

Q35 → How are step-up transformers used in the National Grid?

Question 131

Step-up transformers increase the voltage from power stations to very high values (thousands of volts)

Answer 131

which reduces the current in transmission cables.

Question 132

Q36 → Why is reducing current important in power transmission?

Question 133

Reducing current decreases the amount of energy lost as heat in the wires

Answer 133

making transmission more efficient.

Question 134

Q37 → How are step-down transformers used in the National Grid?

Question 135

Step-down transformers reduce the high transmission voltage to lower

Answer 135

safer levels for use in homes and factories.

Question 136

Q38 → Why must the voltage be reduced before reaching homes?

Question 137

The voltage must be reduced to safer levels because very high voltages used in transmission would be dangerous for domestic and industrial use.