CHAPTER ALTERNATING CURRENT - xraykamarul · CHAPTER 6: Alternating Current 6.2 Alternating and...

HDR102

SCHOOL OF MEDICAL IMAGINGFACULTY OF HEALTH SCIENCES

PREPARED BY:MR KAMARUL AMIN BIN ABDULLAH

CHAPTER 6

PHYSICS FOR RADIOGRAPHERS 1

ALTERNATING CURRENT

of 52

TOPIC

CHAPTER 6: Alternating Current

TOPIC

LEARNING OUTCOMES

At the end of the lesson, the student should be able to:-

Explain what is electrical current including the concept of electron and

current.

Differentiate between alternating and direct current including the source

and usage.

Explain the generation of alternating current.

Describe the principles and build up of generators.

Explain the single and three phases generators.

Explain the sine wave including the frequency, distance and amplitude with

factors affecting it.

of 52

TOPIC


TOPIC

TOPIC OUTLINES

INTRODUCTION

6.1 Electrical Current

6.2 Alternating and Direct Current

6.3 The Principles and Build Up of Generators

6.4 Generation of Alternating Current

6.5 One and Three Phases Generators

6.6 Sine Waves

6.3 References

of 52

TOPIC


TOPIC

INTRODUCTION

The concept of electron and

current

What is an electric current?

What are charge carriers?

of 52

TOPIC


TOPIC


For current to flow you must have a complete circuit.

A power source is needed to create a POTENTIAL DIFERENCE.

When these conditions are met free electrons move about inside the metal.

Direction of current flows in the circuit.

Direction of electrons flow in the circuit.

of 52

TOPIC


TOPIC


The unit of current is the Ampere (A)

The symbol for current is I

The unit of charge is the coulomb (C)

The coulomb is defined as equal to the charge flow in one second when the

current is one Ampere.

The symbol of charge is Q

The equation is Q = It

of 52

TOPIC


TOPIC


The current from a battery is

always in the same direction.

One end of the battery is positive

and the other end is negative.

The direction of current flows

from positive to negative.

This is called direct current, or

DC.

Figure 1: DC circuit and waveform.

6.2.1 Direct Current (DC)

of 52

TOPIC


TOPIC


If voltage alternates, so does

current.

When the voltage is positive, the

current in the circuit is

clockwise.

When the voltage is negative the

current is the opposite direction.

This type of current is called

alternating current, or AC.Figure 2: AC circuit and waveform.

6.2.2 Alternating Current

of 52

TOPIC


TOPIC


AC current is used for almost all high-power applications because it is easier

to generate.

It is cheaper than Direct Current (DC).

It can be transmitted over long distances.

The value of voltage AC can be changed easily, using transformer.

6.2.3 Advantages of Alternating Current (AC)

of 52

TOPIC


TOPIC

6.3 The Principles and Build Up Generators

The basic principle behind generator is Faraday’s law itself when ever:-

a) a conductor cut a magnetic flux and an emf is induced in it and

b) if the circuit is closed a current will through it.

Figure 3: The generator.

of 52

TOPIC


TOPIC

6.3 The Principles and Build Up Generators

Therefore the essential parts of a generator include magnetic field and

conductors to cut the magnetic flux produced by the field.

Figure 4: The

AC generator.

of 52

TOPIC


TOPIC

6.4 Generation of AC

A = is moving along (parallel to) the lines of force - cutting NO lines of force,

NO emf is induced.

B = it cuts more and more lines of force per second/ more directly across the

field (lines of force), the emf induced in the conductor is maximum.

of 52

TOPIC


TOPIC

6.4 Generation of AC

C = the loop is once again moving in a plane parallel to the magnetic

field, and no emf is induced in the conductor

D = it cuts fewer and fewer lines of force. The induced emf (voltage)

decreases from its peak value.

of 52

TOPIC


TOPIC

6.5 Single and Three Phase Generators

A generator is a device that converts mechanical energy (motion) into

electrical energy (current – voltage).

of 52

TOPIC


TOPIC


The basic generator consists of a

loop of wire wound on an

armature drum residing within a

magnetic field (B) produced by a

permanent magnet.

Each end of the loop is connected

to a slip ring which conducts

electricity.

Attached to each slip ring are

electrical contactors called

“brushes”.

Figure 5: The basic generator.

6.5.1 Basic Generator

of 52

TOPIC


TOPIC


A generators with a single source or AC voltage is called a Single-Phase

generator.

Flux density

B [T]

l

d

Figure 6: Generator for single phase Figure 7: Current produced at terminal

6.5.2 Single Phase Generator

of 52

TOPIC


TOPIC


Three-Phase Generator is a generator built with three loops at 120 degrees.

Figure 8: Instead of using one coil only , three coils are used

6.5.3 Three Phases Generator

of 52

TOPIC


TOPIC

6.6 Sine Waves

Waves transfer energy from one point to another without transferring matter.

They consist of disturbances which transfer the energy in the direction the

wave travels without transferring matter.

The basic shape of the wave generated is that of a sine wave.

of 52

TOPIC


TOPIC

6.6 Sine Waves

Is composed of several repeating

parts called "cycles".

One complete cycle having a

maximum value above, and a

maximum value below, the

reference line.

One cycle has one crest (peak +ve)

and one trough (peak –ve).Figure 9: A sine wave.

6.6.1 Cycle

of 52

TOPIC


TOPIC

6.6 Sine Waves

Is the distance between peak to

another peak/ crest to crest/

trough to trough.

Wavelengths vary from a low to

high frequencies.

express wavelengths in meters.

Figure 9: A sine wave.

6.6.2 Wavelength

of 52

TOPIC


TOPIC

6.6 Sine Waves

The height of a wave crest above

the reference line is called the

amplitude of the wave.

The amplitude of a wave gives a

relative indication of the amount of

energy the wave transmits - in other

words the signal's strength.


6.6.3 Amplitude

of 52

TOPIC


TOPIC

6.6 Sine Waves

The number of cycles of a

continuous wave per unit of time

is called the frequency of the

wave

Is measured in Hertz. One Hertz

(abbreviated Hz) is one cycle per

second.

Therefore, if 5 waves pass a point

in one second, the frequency of

the wave is 5 cycles per second or

5 Hz.


6.6.4 Frequency

of 52

TOPIC


TOPIC

6.6 Sine Waves

Signal attenuation. This is a fancy way of saying, the farther a signal goes, the

weaker it gets. Attenuation can be by absorption, reflection, or refraction of

the radio wave energy.

Interference. The atmosphere is FULL of EM waves of all kind - the more

there are in the area the radio is being used, the more interference there is

and the poorer the range and quality of transmission and reception.

6.6.5 Factors Affecting the Waves

6.6.5.1 Factors that reduce the range include:-

of 52

TOPIC


TOPIC

6.6 Sine Waves

The ability of radio waves to penetrate through or bend around certain

obstructions.

The power output of the radio - the greater the power the less the

attenuation of the waves.

Antenna height - obviously the taller the transmission and reception

antennae, the greater the range.

6.6.5.2 Factors that increase range include:

6.6.5 Factors Affecting the Waves

of 52

TOPIC


TOPIC

Answer the questions.

SAMPLE OF ACTIVITY

Which of the following statements BEST describe wavelength?

Quiz

It is the time taken for the electromagnetic field to undergo one complete cycle of oscillation

It is the distance between two successive points in a wave.

It is the number of waves that passes a particular point in a given

time frame.

It is the intensity of the wave defined by its maximal height

of 52

TOPIC


TOPIC

SUMMARY

The unit of current is the Ampere (A)

The unit of charge is the coulomb (C)

The coulomb is defined as equal to the charge flow in one second when the

current is one Ampere.

The Direct Current is always in the same direction.

In Alternating Current, if voltage alternates, so does current.

A generator is a device that converts mechanical energy (motion) into

electrical energy (current – voltage).

of 52

TOPIC


TOPIC

NEXT SESSION PREVIEW

CHAPTER 7: TRANSFORMERS

In chapter 7, students will be introduced to the principles and

concepts of transformer.

of 52

TOPIC


TOPIC

6.7 References

No. REFERENCES

1 Ball, J., Moore, A. D., & Turner, S. (2008). Essential physics for

radiographers. Blackwell.

2 Bushong, S. C. (2008). Radiologic science for technologists. Canada:

Elsevier.

of 52

TOPIC


TOPIC

APPENDIX

FIGURE SOURCE

Figure 1 http://www.actors.co.ke/en/news/Energy1.jpg

Figure 2 http://intechweb.files.wordpress.com/2012/03/shutterstock_77399518.jpg

Figure 3 http://www.solarenergybook.org/wp-content/uploads/2009/12/solar-energy-

example.gif

Figure 4 http://www.petervaldivia.com/technology/energy/image/potencial-and-

kinetic.bmp

Figure 5 http://iws.collin.edu/biopage/faculty/mcculloch/1406/outlines/chapter%206/S

B7-2b.JPG

Figure 6 http://www.petervaldivia.com/technology/energy/image/potencial-and-

kinetic.bmp

Figure 7 http://www.physics4kids.com/files/art/motion_energy1_240x180.jpg

Figure 8 http://www.sciencebuilder.com/michigan/science/images/p/potentialenergy.j

pg

Figure 9 http://4.bp.blogspot.com/_V7DuEO3c2E8/S-

b2PZfOXZI/AAAAAAAAADk/KKXoueyon2I/s1600/One-balanced-rock.jpg

CHAPTER ALTERNATING CURRENT - xraykamarul · CHAPTER 6: Alternating Current 6.2 Alternating and...

Documents

Transcript of CHAPTER ALTERNATING CURRENT - xraykamarul · CHAPTER 6: Alternating Current 6.2 Alternating and...