transformers for IGCSE Physics, GCE O level Physics

Summary

This script explores the concept of mutual induction in transformers, explaining how an electromagnet induces an EMF in a second solenoid. It delves into the workings of transformers, distinguishing between step-up and step-down types, and their crucial role in the National Grid to minimize energy loss through high voltage transmission. The script also highlights the inefficiency of transformers with DC and the importance of AC in power transmission, concluding with a demonstration of power loss calculations in cables at different voltages.

Takeaways

• 🧲 Mutual Induction: When an electromagnet is switched on or off, a momentary EMF is induced in a nearby solenoid due to the changing magnetic field.
• 🔧 Steady Current No EMF: A steady current through an electromagnet does not induce EMF in a secondary solenoid because the magnetic field remains constant.
• 🔄 Alternating Current Effect: Using an alternating power supply results in an alternating magnetic field that induces an alternating EMF in the secondary solenoid.
• 🔗 Increasing Induced EMF: The induced EMF in the secondary solenoid can be increased by adding more turns to the coil or using an iron core that extends through the secondary solenoid.
• 🌐 Principle of Transformers: Transformers operate on the principle of mutual inductance to transfer electrical energy efficiently between two coils.
• ⚙️ Components of a Transformer: A basic transformer consists of an AC input power supply, a primary coil, an iron core, and a secondary coil.
• ⏫⏬ Types of Transformers: There are step-up transformers that increase voltage and step-down transformers that decrease voltage, differentiated by the number of turns on their coils.
• 🔌 National Grid Application: Transformers are crucial in the National Grid for transmitting electricity at high voltages and low currents to minimize energy loss.
• ⚡ High Voltage Dangers: High voltage transmission requires safety measures such as elevated pylons or underground cables to avoid danger.
• 🔌 AC vs. DC in Transformers: Transformers work with AC currents, which can be easily stepped up or down, unlike DC which does not induce EMF due to its steady magnetic field.
• 📉 Power Loss Calculation: Demonstrates that high voltage transmission reduces power loss in cables, as shown by comparing power losses at different voltages and currents.

Q & A

What is the phenomenon of mutual induction?

Mutual induction occurs when an electromotive force (EMF) is induced in a secondary solenoid due to the changing magnetic field created by a current in a nearby primary solenoid.

Why is there no EMF induced in the second solenoid with a steady current through the electromagnet?

No EMF is induced in the second solenoid with a steady current because the magnetic field is not changing; mutual induction requires a varying magnetic field.

What happens when an alternating power supply is used instead of a DC power supply in an electromagnet?

An alternating power supply creates an alternating magnetic field around the electromagnet, which interacts with the secondary solenoid, inducing an alternating EMF in it.

How can the induced EMF in the second solenoid be increased?

The induced EMF in the second solenoid can be increased by increasing the number of turns on the secondary solenoid, using an iron core in the electromagnet, or having the iron core go right through the secondary solenoid.

What is a transformer and what is its primary function?

A transformer is an electrical device used to increase or decrease the voltage of an AC current. It works based on the principle of mutual induction between two coils.

Why are transformers not effective with DC power?

Transformers are not effective with DC power because DC creates a steady magnetic field that does not interact with the coil to induce an EMF.

What are the two main types of transformers?

The two main types of transformers are step-up transformers, which increase the voltage of an input power supply, and step-down transformers, which decrease the voltage.

How do transformers help reduce energy loss in the National Grid?

Transformers help reduce energy loss by allowing electricity to be transmitted at high voltages and low currents, which minimizes the amount of energy lost as heat in the transmission lines.

What is the significance of using high voltage transmission lines for long-distance electricity transmission?

High voltage transmission lines are used to minimize energy loss during long-distance transmission. By increasing the voltage and reducing the current, thinner, lighter, and cheaper cables can be used.

Why is alternating current preferred for electricity transmission over long distances?

Alternating current is preferred for long-distance transmission because it can be easily stepped up and down in voltage using transformers, which helps in minimizing power loss and efficiently transmitting electricity.

How does the power loss in a cable relate to the current flowing through it?

The power loss in a cable is directly proportional to the square of the current flowing through it (as per the formula Power Loss = Current^2 * Resistance). Therefore, reducing the current for the same power transmission reduces the power loss.

Outlines

00:00

🌐 Principles of Electromagnetism and Transformers

This paragraph explains the fundamental principles of electromagnetism, specifically mutual induction, which is the process by which an electromagnet induces an electromotive force (EMF) in a nearby solenoid. It describes how a steady current does not induce an EMF, but a changing magnetic field does. The concept of transformers is introduced, which are devices that use mutual induction to either increase or decrease the voltage of an alternating current (AC). The paragraph also details the components of a transformer, the types of transformers (step-up and step-down), and their function in electrical grids to transmit electricity efficiently with minimal energy loss. The importance of using iron cores and the inability of transformers to work with direct current (DC) due to the lack of a changing magnetic field is also highlighted.

05:00

🔌 High Voltage Transmission and Energy Efficiency

The second paragraph delves into the practical application of transformers in high voltage transmission systems like the National Grid. It illustrates how step-up transformers reduce current and increase voltage, making it safer and more efficient to transmit electricity over long distances. The paragraph provides an example of how a power station's output is transformed to minimize energy loss due to heat in transmission lines. It also explains the use of step-down transformers to adjust voltage levels for safe use in urban areas and homes. The importance of alternating current (AC) in this process is emphasized, as it allows for easy voltage transformation, unlike direct current (DC). The paragraph concludes with a comparison of power loss in cables at different voltages, demonstrating the energy efficiency of high voltage transmission.

Keywords

💡Mutual Induction

Mutual induction is a fundamental concept in electromagnetism where an electromotive force (EMF) is induced in a secondary coil due to a changing magnetic field created by a current in a primary coil. In the video, mutual induction is the core principle behind the operation of transformers, where it is used to transfer electrical energy efficiently between two coils. The script explains that when the electromagnet is switched on or off, a momentary pulse induces an EMF in the second solenoid due to the rapid change in the magnetic field.

💡Electromagnet

An electromagnet is a type of magnet whose magnetic field is generated by the flow of electric current. In the context of the video, the electromagnet is used to create a changing magnetic field that induces an EMF in a nearby solenoid. The script mentions that when the electromagnet is switched on or off, it is equivalent to moving a magnet rapidly towards or away from the second solenoid, thus inducing an EMF.

💡EMF (Electromotive Force)

Electromotive force, or EMF, is the electrical energy per unit charge that is available to do work. In the video, EMF is induced in the second solenoid due to the changing magnetic field from the electromagnet. The script provides examples of how a momentary pulse of EMF is induced when the electromagnet is switched on or off, and how an alternating EMF is induced when an alternating current flows through the electromagnet.

💡Alternating Current (AC)

Alternating current is a type of electrical current that reverses direction periodically. The video script explains that when an AC power supply is used, it creates an alternating magnetic field around the electromagnet, which in turn induces an alternating EMF in the secondary solenoid. This is in contrast to a steady current, which does not induce an EMF when flowing through the electromagnet.

💡Transformer

A transformer is an electrical device that uses mutual induction to increase or decrease the voltage of an AC current. The script describes a transformer as having four main components: the primary coil, secondary coil, iron core, and AC input power supply. Transformers are essential for stepping up or stepping down voltage levels in electrical systems, as they allow for efficient transfer of electrical energy between coils.

💡Step-up Transformer

A step-up transformer is a type of transformer that increases the voltage of an input power supply. The script explains that this is achieved when the number of turns on the primary coil is less than the number of turns on the secondary coil. This allows for the transmission of electricity at high voltages and low currents, reducing energy losses in the form of heat.

💡Step-down Transformer

A step-down transformer decreases the voltage of an input power supply. According to the script, this is done by having more turns on the primary coil than on the secondary coil. Step-down transformers are used to reduce the high voltages from transmission lines to safer levels for use in homes and businesses.

💡National Grid

The National Grid refers to the network of wires and cables that carry electrical energy from power stations to consumers. The video script discusses how transformers are used in the National Grid to transmit electricity at high voltages and low currents to minimize energy loss due to heating effects in the transmission lines.

💡High Voltage Transmission

High voltage transmission is the practice of sending electricity over long distances using high voltages and low currents. The script explains that this method reduces energy loss in the form of heat by minimizing the current in the wires. Transformers are used to increase the voltage for transmission and decrease it for safe use at the point of consumption.

💡Power Loss

Power loss refers to the reduction in electrical power due to resistance in the transmission lines, which results in energy being wasted as heat. The script provides calculations to illustrate how power loss is minimized when electricity is transmitted at high voltages, as the current is reduced, leading to less energy wasted as heat in the cables.

💡Iron Core

An iron core is a soft magnetic material used in transformers that can be easily magnetized and demagnetized. The script explains that the iron core in a transformer helps the changing magnetic field created by the primary coil to pass through to the secondary coil, thereby inducing an EMF. The use of an iron core enhances the efficiency of mutual induction in transformers.

Highlights

Candidates are expected to have a thorough understanding of the syllabus and details outlined in the accompanying figure.

Mutual induction occurs when an electromagnet is switched on, inducing an EMF in the second solenoid for a momentary pulse.

A steady current through the electromagnet does not induce EMF in the second solenoid, as the magnetic field is not changing.

When the electromagnet is switched off, an EMF is induced in the opposite direction in the second solenoid for a momentary pulse, equivalent to pulling a magnet away quickly.

An alternating power supply creates an alternating magnetic field, inducing an alternating EMF in the second solenoid.

The induced EMF in the second solenoid can be increased by increasing the number of turns on the secondary coil.

Using an iron core in the electromagnet that goes through the secondary solenoid enhances mutual inductance.

Transformers apply the principle of mutual inductance to efficiently transfer electrical energy between two coils.

A transformer has four main components: AC input power supply, primary coil, iron core, and secondary coil.

Iron is used in transformers because it is a soft magnetic material that is easily magnetized and demagnetized.

Transformers will not work with DC as it creates a steady magnetic field that does not induce EMF in the coil.

There are two types of transformers: step-up and step-down, which increase or decrease the voltage of an input power supply respectively.

The voltage and current in a transformer are related by the ratio of turns on the primary and secondary coils.

Transformers help reduce energy loss in transmission by allowing electricity to be transmitted at high voltages and low currents.

National Grids use transformers to minimize heat loss by transmitting electricity at high voltages and decreasing it for household use.

High voltage transmission lines are used to minimize power loss over long distances by reducing the current.

AC is used for transmission because it can be easily stepped up and down in voltage using transformers, unlike DC.

Calculations demonstrate that less power is lost from a cable when power is transmitted at high voltage.

The video aims to be helpful and encourages viewers to subscribe, share, like, and leave positive comments for support.

Transcripts

[Music]

candidates are expected to have a

thorough understanding of the syllabus

details outlined in the accompanying

figure Mutual

induction as the electromagnet is

switched on an EMF is induced in the

second solenoid but only for a momentary

pulse this effect is equivalent to

pushing a magnet toward the second

solenoid very fast with a steady current

through the electric no EMF is induced

in the second solenoid because the

magnetic field is not changing as the

electromagnet is Switched Off an EMF is

induced in the opposite direction in the

second solenoid but only for a momentary

pulse this effect is equivalent to

pulling a magnet away from the second

solenoid very fast when an alternating

power supply is used instead of the DC

power supply an alternating current

flows through an electromagnet creating

an alternating magnetic field around it

this alternating magnetic field

interacts with second solenoid inducing

an alternating EMF in it the induced EMF

in the second solenoid can be increased

by increasing the number of turns on the

secondary Sol solenoid using an iron

core in the electromagnet that goes

right through the secondary

solenoid this principle is applied in

Transformers where the mutual inductance

between two coils allows for the

efficient transfer of electrical energy

between

them a simple

Transformer a Transformer is an

electrical device that can be used to

increase or decrease the voltage of an

AC current it works by Mutual

induction it has four main

components the AC input power

supply primary coil iron core and

secondary coil iron is used because it

is soft magnetic material that is easily

magnetized and

demagnetized when an alternating current

flows through the primary coil creating

and changing magnetic field around it

the iron core is easily magnetized so

the changing magnetic field passes

through it to the secondary coil this

changing magnetic field interacts with

the secondary coil inducing an

alternating voltage or EMF in the

secondary coil that has same frequency

as the input alternating

voltage if the secondary coil is part of

a complete circuit it will cause an

alternating current to flow Transformers

will not work with DC because it creates

a steady magnetic field that does not

interact with the coil and induce an

EMF there are two types of Transformers

as the step up and step down

Transformers Step up

Transformer it increases the voltage of

an input power supply meaning VP is less

than VSS and the number of turns on the

primary coil is less than the number of

turns on the secondary coil Step Down

Transformer it decreases the voltage of

an input power supply meaning V

is more than vs and the number of turns

on the primary coil is more than the

number of turns on the secondary coil

assuming all magnetic field lines pass

through both coils and there is no

energy lost due to heating effects the

following equations apply where VP is

the voltage in the primary coil vs is

the voltage in the secondary coil NP is

the number of turns on the primary coil

NS is the the number of turns on the

secondary coil the output power will be

the same as the input power of Supply

where VP is the voltage in the primary

coil IP is the current in the primary

coil VSS is the voltage in the secondary

coil is is the current in the secondary

coil National Grid are networks of wires

and cables that carry electrical energy

from Power stations to consumers such

factories and

homes however currents in Long wires can

lose lots of energy in the form of heat

the larger the current the greater the

amount of energy lost if the current in

the wires is kept to a minimum the heat

losses can be

reduced Transformers help us do this

Transformers are used in National Grids

so that the electricity is transmitted

as low currents and as at high

voltages typically a large Power Station

produces a current of 20,000 amp at a

voltage of 33,000 volts the high current

is fed to a step-up Transformer which

greatly decreases the size of the

currents and increase the size of the

voltages these stepup Transformers

increase the voltage of the electricity

to approximately 400,000 volts high

voltages like these can be extremely

dangerous so the cables are supported

high above the ground on

pylons as the cables enter town and

cities they are buried

underground close to where the

electrical energy is needed the

electricity is sent through a Step Down

Transformer that decreases the voltage

to approximately 230 volts while at the

same time increasing the

current high voltage

transmission when electricity is

transmitted over large distances the

current in the wires Heats them

resulting in energy loss to minimize

this loss we use high voltage

transmission lines by using a

Transformer to increase the voltage the

current is

reduced this means we can use thinner

lighter and cheaper cables to transmit

the same amount of power for example

aluminum cable alternating current is

used for the transmission because

alternating current can be easily

stepped up and down in voltage using

Transformers this means that

Transformers only work with AC

Transformers will not work with

DC the calculation demonstrates why less

power is lost from a cable if power is

transmitted through it at high

voltage the first circuit the power

input is 2,000 watt 200 volts and cable

resistance of 2 Ohms a current flows

through the cable can be calculated ated

by power equals current time voltage to

substitute the power is 2,000 and

voltage is 200 the results of current is

10

amp when a current flows through a

resistance it has a heating effect so

power is wasted the power loss can be

calculated by power equals current

squared times

resistance to substitute current is 10

and resistance is two

the results of power loss is 200 Watts

the second circuit increases in the

voltage from 200 to 2,000 volts while

the power and resistance of the cable

remain the same a current flows through

the cable reduces to 1 ampere the power

loss in the cable becomes 2 Watts these

calculations show the power losses in a

cable when the same amount of power is

sented high voltage is less than the low

voltage

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