Chapter 22 - Electromagnetic Induction Flashcards by 颖臻范

How does the D.C voltage-time graph looks like?

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How does the A.C voltage-time graph looks like?

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How does the D.C current-time graph looks like?

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How does the A.C current-time graph looks like

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How to change a A.C current to a D.C current?

By adding a diode in the circuit. Diode only allow current to flow in one direction

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What does LED stands for?

Light emitting diode

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What is the similarity and difference between normal diode and LED?

both allow the current to flow in one direction

LED ,however, give out light when current pass through

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What are the two advantages of LED?

Small

Have a long life

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Explain why there will be an induced current when a magnet is push into the solenoid.

When the magnet is pushed inside the coil, the magnetic field line from the magnet ‘cut’ the coil. There will be a changing magnetic field around the coil, so there will be a induced electromotive force (E.M.F) and thus there will be a induced current produced.

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Explain why there will will not an induced current when a magnet is stationary in the coil.

When the magnet is not moving, the magnetic field from the magnet is not ‘cutting’ the coil, thus there will not be a changing magnetic field, which in turn, no induced current will be produced

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What does electromagnetic induction effect means?

The process which an induced e.m.f is produced in a conductor due to a changing magnetic field

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How to determine the direction of flow of the induced current? (In the case of the solenoid)

Using Len’z Law (In the case of a solenoid), when the magnet is push into the coil, an induced current will form a pole which will oppose the motion of the magnet.

For example, if the magnet is pushing in from the right, with an N-pole entering the coil first, a N-pole will form at the end of the solenoid to repel the N-pole of the magnet.

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What are the three ways to increase the strength of the induced current?

Increase the number of the coil
Increase the strength of the magnet
Increase the speed of the magnet moving in and out of the solenoid

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What is the prior condition for a induced current to be produced?

A CHANGING magnetic field

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How to determine the direction of flow of the induced current ? (in the case of magnet moving up and down in between N and S pole)

Use the Fleming’s right hand rule.
Thumb represent the motion of the magnet
Second finger represent the magnetic field
Middle finger represent the current

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What does a Generator do?

Generator is a device in which a coil is rotated in a magnetic field to produce eletricity

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Hoe does a generator work (Diagram refer to notes)

The coil is made to rotate in the space between the magnet. As the coil rotates, the coil ‘cut’ through the magnetic field, so there will be an induced e.m.f and thus produced an induced current.

Initially, the coil is parallel, as it rotate 180 degree, the current direction is reversed, making the coil continue to turn in a clockwise direction. Thus, an alternating current is produced.

What is the purpose of the SLIP ring

Provide connection between the coil and the outer circuit, so that alternating current can flow in the external circuit
Prevent coil to be entangled

In a simple generator set-up (Diagram refer to notes), why there is no current induced when the coil is vertical?

As the coil is PARALLEL to the field, there is no change in the magnetic field, thus there will be no induced e.m.f and thus no induced current.

In a simple generator set-up, induced e.m.f is maximum when the coil is horizontal, why?

When the coil is horizontal, the rate of change of magnetic field is maximum

3 Factors in GENERATOR affecting the size of e.m.f (There can be other factors)

Speed of rotation
Strength of magnet
Number of turns in the coil

For the graph for factors in GENERATOR affecting size of e.m.f please refer to notes

okay

In a simple transformer set-up, when an electromagnet is placed next to a solenoid and it is switch on and off, why there is a induced current produced in the solenoid?

As we switch on and off the circuit of the electromagnet, there will be a changing magnetic field as the field lines of the electromagnet ‘cut’ through the solenoid. Thus there will be an induced e.m.f and thus there will be an induced current

In a simple transformer set-up, when an electromagnet with D.C current is placed next to a solenoid and it is switch on and off. What are the two modifications can be made to improve on this set-up?

Change the D.C current to A.C current, so that we do not need to switch the circuit on and off physical

Extend the electromagnet (Soft iron) to connect the two solenoid, so that the iron core will help to concentrate the field lines, more field lines will ‘cut’ through the coil and a greater induced current will be produced

What does a transformer do?

A transformer is used to change high voltage to low voltage or vice-versa

What are the two types of transformer?

Step-up Transformer and Step-down Transformer

What is the difference between Step-up Transformer and Step-down Transformer

Step-up transformer is used to increase the voltage, thus it has lesser coil in the primary coil than the secondary Step-down transformer is used to reduce the voltage, thus it has more coil in the primary coil than the secondary coil

For symbol of transformer, refer to notes

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What does a actual simple transformer has (3 things) | Diagram refer to notes

A primary carrying a A.C current A laminated soft iron core a secondary coil with a load

There is a relationship between the number of the coil and the voltage of the primary and secondary coil in a transformer, what is the Formula for that?

Voltage (sec)/ Voltage (pri) = Number (sec)/ Number (pri) | ALWAYS Secondary comes first

What is an ideal transformer?

An idea transformer means that it is 100% efficient, where by there is no energy loss, thus input power is equal to output power

Power formula used in ideal transformer

V(pri) x I(pri) = V(sec) x I(sec)

When the voltage is step down in the transformer, the current will?

Increase

What are the two reasons for why a transformer is unable to be 100% efficient? How to minimise these disadvantage?

Some energy is loss in the form of heat when current flow in coil which have resistance. To minimise this, thick wire are normally used to reduce the resistance, so that lesser heat is produced Energy is loss in the form of eddy current which produced in the iron core during mutual induction. To minimise this, the iron core is LAMINATED.

What will be one design feature to improve the efficiency of a transformer?

Use of laminated iron core. Iron is magnetic material which help to concentrate the field lines, which allow more lines to 'cut' through the coil Iron will not retain magnetism, so it increase the rate of change of magnetic field Laminated Iron reduces eddy current produced during mutual induction

Why in the whole process of transmission of electrical power, a step-up and step down transformer is needed? Explain further.

A step-up and a step-down transformer is needed because this design minimise energy loss during the transmission process, hence, more energy is transmitted into actual use. When the voltage is increase, the current is decreased. Using the formula of P= I X I X R to calculate power loss, a smaller value of I will give a lesser value of P, thus a smaller current will reduce the power loss.

In a C.R.O, what does the Y-plate do?

The Y-plate control the voltage input

In a C.R.O, what does the X-plate/Time base button do?

The X-plate or the time base button control the frequency. | Once it switch on, there will be an A.C current running on the X-plate

As the voltage input of the Y-plate reduced, what will happen to the wave size?

It will become higher

As the frequency input of the time base reduces, what will happen to the wave number?

There will be fewer wave

What is the advantage of C.R.O over Voltmeter?

C.R.O can measure voltage of an A.C current