04•Ch 4(F)

filament

cathode gridcontrol

focussinganode

a.c. 6 V

accelerating anode

Electron gun

V.H.T

Deflection system

vacuumelectron beam

image on screen

fluorescent screen

+-

Y- plate

X- plategraphite layer

Longman Project! Overhead Transparencies Physics Form

5

Pearson Malaysia Sdn.Bhd. 2007

CHAPTER

444

58

Electronics

4.1 Understanding the Uses of the Cathode Ray Oscilloscope (CRO)

Cathode Ray Oscilloscope (CRO)

Function

To heat up the cathode.

To release electrons when heated.

To control the number of electronspassing through it.

To focus the electron beam onto thescreen.

To accelerate the electron beam.

To move the electron beam vertically (up and down).

To move the electron beam horizontally.

To convert kinetic energy of the electronbeam into light.

To conduct the electrons from the screeninto the earth.

Sub-components

Filament

Cathode

Grid control

Focussinganode

Acceleratinganode

Y plates

X plates

Fluorescentscreen

Graphitecoating

Maincomponents

Electrongun

Deflectionsystem

Fluorescentscreen


5


CHAPTER

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Electronics


Function of CRO Parts

negativelycharged

strong electrons pass through

CRO

cathode

eeee

filament

6 V

heat

faster electrons

accelerating anode

X2

y2

y1X1

X2ee

Y-platesX-plates

graphitecoating

electrons are earthed

electron beamis deflecteddownwards

(more positive)

electron beamwith kinetic energy

light

heatscreen

focussing theelectron beam

focussing anode

eeee

xxxx

e

(morepositive)

e


5


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Electronics


Properties of Cathode Ray

1 It travels in a straight line.

2 (a) It carries negative charges.(b) It produces an electric current in opposite direction.

3 It carries high kinetic energy.

4 It illuminates the fluorescent screen.

5 It is deflected by the electric field.

6 It is deflected by the magnetic field.

electric current

moving electronsee ee

electron beamwith highkinetic energy

turns green whenstruck by electrons

dark shadow

blocks the electrons to form adark shadow on the screen

e

+

-

- e --

+

e

to the right

magnet

S

N magnet

image isshifted tothe right

S

N


5


CHAPTER

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Electronics


CRO as a Measuring Instrument

screen

voltagescale

time-base

Volt/cm s/cm

Focus

Brightness

Shift - X

Shift - Y

On/Off

Input+-

Time-base " OFF "

Time-base " ON "Time-base " ON "

1.5 cm

Battery voltage = 1.5 V Peak voltage = 1.5 V

1V cm-1

Voltage scale

Time-base " OFF "

D.C. sourcebattery

A.C. source transformer

1.5 cm3 cm

3 cm

(a) Measuring voltage


5


CHAPTER

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Electronics


CRO

radar station

don-comingaeroplane

microwave4 cm

(b) Measuring time and frequency

Time taken between P and Q = 8 10 ms = 80 msPeriod of wave, T = 4 10 ms = 40 ms

Frequency of wave, f = = = 25 Hz

(c) Measuring time and distance

Time-base of CRO = 1 ms cm1

To and fro time registered, t = 4 1 ms = 4 msVelocity of microwave, v = 3 108 m s1

Distance between the aeroplane and the radar station,

d = =

= 6 105 m= 600 km

(3 108)(4 103)2

vt2

140 103

1T

Voltagescale

time-base

1V cm-1 10 ms cm-1

8 cm

8 cm

2 cm

T

QP


5


CHAPTER

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Electronics


Displaying Waveforms (with time-base)

R = resistor

A.C. sourceD.C. battery

+

R

-

+-

R

+-

1 2

A.C. source

RDiode

R

D.C. dynamo

+-+-

3 4

Radio

N

S

Magnet

+

-

-

fish

TV

Computer

D.C. Dynamo

+ -Battery

Heartpatient

CRO

+

e

Y-plate

X-plate


5


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Electronics


Some Uses of the CRO

In TV/computer

Measuring distanceAs a voltmeter

Waveform ofheartbeat

Waveforms inelectrical/electronic parts

Deflection bymagnetic fieldWaveforms for

A.C./D.C. sources

Deflection by electric field

CRO


5


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Electronics

4.2 Understanding Semiconductor Diodes

Semiconductor

charge carriers : electrons and holes

Valency-4

Doped with atomswith valency-3

Doped with atomswith valency-5

Conductor

Low resistance

Plenty of freeelectrons

Semiconductor

Between conductorand non-conductor

Very little freeelectrons

Conduction can beimproved by doping

Non-conductor

High resistance

No free electrons

Pure semiconductor

Si SiliconGe Germanium

p type

: creates more positive holes

n type

: creates moreelectrons

Si Si Si

Si Si

Si Si Si

Si Si Si

Si Si

Si Si Si

lack of one electron a positive hole

extra electron free electron

p n

RectifierAmplifier andautomatic switch

pnp

npn


5


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Electronics


p-n Junction

more electronsthan holes

positive hole electron

p n

fused barrierhinders electronsand holes from passingthrough itno conduction of charges

more holesthan electrons

structure

symbol

uses

Basic characteristics

(i) As a diode (ii) As a transistor

Uses of p-n junction

I p n

x

L

e

A

y

light bulb ammeter

hole electron

X y

+

conduction band

-


5


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Electronics


Conduction in p-n Junction

1 Forward bias

Potential at X is

Potential at Y is

Conduction band becomes

Holes and electrons at the conduction band are

Resistance for conduction is

Electric current flows from

positive

negative

narrower

closer

smaller

X toY


5


CHAPTER

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Electronics


p n

x

L A

y

light bulb ammeter

hole electron

X y

+

conduction band

-

2 Reverse bias

Potential at X is

Potential at Y is

Conduction band becomes

Holes and electrons at the conduction band are

Resistance for conduction is

Electric current

negative

positive

broader

further apart

higher

does not flow

Conduction in p-n Junction


5


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Electronics


p-n Junction/Diode as a Rectifier (A.C. : D.C.)

A.C.

D.C.

the wave is smoothened

CRO

D.C.CRO

A.C.diode

capacitor C

switch S

R

CRO

1

2

3

P

Q

R

1 Half-wave rectification


5


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Electronics

4.1 Understanding SemiconductorDiodes

p-n Junction/Diode as a Rectifier (A.C. : D.C.)

D1 D2

D4 D3

A.C. +-

A.C.

D.C.

the wave is smoothened

CR

CRO

1

CRO

2

CRO

3

switch S

A

B

D.C.

C

2 Full-wave rectification


5


CHAPTER

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Electronics

4.3 Understanding Transistors

Transistor

Potential at c

Potential at b

Potential at e

Current flows from

Relationship of currents

n-p-n type

positive

positive

negative

b : e, c : e

Ie = Ib + Ic

n-p-n type

p-n-p type

IcIb

Ie

collector

baseb

e

e

b

c c

emitter

p

p

n

p-n-p-type

negative

negative

positive

e : b, e : c

Ie = Ib + Ic

collector

baseb

e

c

emitter

e

b IbIc

Ie

c

n

p

n

Some examples oftransistors


5


CHAPTER

444

72

Electronics


Ic /mA

Ic /AGe

Ge Si

Si

Vo, threshold voltage V/ VV/V

Transistor

Potential difference across be, Vbe Vo

Potential difference across be, Vbe Vo

Is Ohms law obeyed? Why?

Current Ic = 0

Ic 0

No. I is not directlyproportional to V

Graph of Ic against V


5


CHAPTER

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Electronics


Uses of Transistor

1 Amplifier

Function of components

Current, IbMicrophone, M

Loudspeaker, L

Amplifier (transistor T )

Capasitor, C

Amplification

To activate Ic to flow through L

To convert sound into electrical impulses

To convert electrical impulses into sound

To amplify the output in L

To block direct current

= gradient of graph Ic against IbIcIb

Amplifier circuit Graph of Ic vs Ib

amplifier

C

c

L

M

Ib

Ice

btransistor, T

sound Ic /mA

Ib /AIo Thresholdcurrent


5


CHAPTER

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Electronics


(a) (i) R1 : light sensitive resistor (LSR)

: With light on, the resistance of LSR is decreased. Hence, the load L will function.

(ii) R1 : termistor (heat sensitive resistor)

: When there is heat/high temperature, the resistance of R1 is decreased. Hence, the sprinkler system will be activated.

(b) (i) If R2 is a LSR: switch works in darkness(ii) If R2 is a termistor : switch works in cold temperatures

Uses of automatic switch

Examples of load, L

Fire alarm system, security alarm system,switching ON/OFF a certain circuit, etc.

Flashing light, siren, switching ON/OFF acircuit, etc.

Examples on usage

2 Automatic switch

Basic circuit Basic principle

Current Ib controls Ic. Current Ic activates the load L to

function. The load L will be activated if

resistance R1 is decreased orresistance R2 is increased.

R1

R2

R

e

c

L

Ic

Ib

b


5


CHAPTER

444

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Electronics

4.4 Analysing Logic Gates

Logic Gate

Many inputs

Symbols, Booles equations and truth table

Only ONE outputElectronic

components

A

A

A

A

A

A

A

B

B

B

B

B

B

X

X

X

X

X

X

X

A + B = X

A + B = X

A B = X

A B = X

A = X

A B = X+

A B = X+X-NOR

X-OR

NOR

NAND

OR

AND

NOT

Name oflogic gate Logic symbols

Booles'equations

TRUTH TABLE

INPUT OUTPUTA B X0 - 11 - 00 0 00 1 01 0 01 1 10 0 00110011001100110011

1010101010101010101

1111110100001101001


5


CHAPTER

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Electronics


(a)

Circuit Truth table

AND gate

AB

input

output X

A B X

0 0 0

0 1 0

1 0 0

1 1 1

Input Output

keyhole

digitalaccess user name

PIN

Log-in

A

B

X

** ** **

PHYSICS

WELCOME

The safe willopen when theright key ANDthe right digitalcombinationsare used.


5


CHAPTER

444

77

Electronics


(b)

Circuit Truth table

OR gate

XA B

A B X

0 0 0

0 1 1

1 0 1

1 1 1

Input Output

switch B

switch A

lamp X

Lamp X can beoperated by eitherswitch A or switch B


5


CHAPTER

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78

Electronics


(c)

Switch A has zero resistance.

When A is opened logic 0, the lamp X is lit.

When A is closed logic 1, the lamp X is not lit.

NOT gate

Circuit Truth table

R

XA

Input Output

A X

0 1

1 0

AB

C

S

(Carried forward= A B )

(Summation= A B + A B )Input

Output

(Subtraction= A B + A B )

A

B

L

S

(On loan = A B)

Input

Output

Subtraction operator

For subtraction of binarynumbers


5


CHAPTER

444

79

Electronics


Binary Addition & Subtraction Operator

Addition operator

Input

A

0

0

1

1

B

0

1

0

1

S

0

1

1

0

C

0

0

0

1

Output Input

A

0

0

1

1

B

0

1

0

1

S

0

1

1

0

L

0

1

0

0

Output

Detailedcircuit

For addition of binarynumbers

Truthtable

A 0 0 1 1B +0 +1 +0 +1

S 0 1 1 1 0C

Function

Operation

A 0 1 0 1 1B 0 1 0 1

S 0 1 1 0L

SQ

G2

G1

R

Input Output

Q


5


CHAPTER

444

80

Electronics


Flip-Flop

Circuit

The two outputs are of opposite logic. It possesses a memory the logic of

the output persists even if the inputsare altered.

Input

S

1

1

1

0

1

Row

(a)

(b)

(c)

(d)

(e)

R

1

0

1

1

1

Q

1

0

0

1

1

Q

0

1

1

0

0

Output

Stand-by

Set (Flip)

Hold

Reset (Flop)

Hold

Operationmode

Characteristics

Truth table

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04•Ch 4(F)

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