Form 5 Physics Chapter 4 - Teacher's Copy

Name:……………………………………………………. Electronics/Form 5 4. ELECTRONICS SECTION A Structured Items Instruction: Answer all questions in this section.

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4.1 Understanding the uses of the Cathode Ray Oscilloscope (C.R.O)

A student is able to : explain thermionic emission. • Describe the properties of cathode rays. • Describe the uses of a cathode ray oscilloscope. -- Measure potential potential difference difference using the C.R.O. -- Measure short short time intervals intervals using the C.R.O. -- Display wave wave forms using using the C.R.O. • Solve problems based on the C.R.O. display •

1. 2.

Thermionic emission is the process where by electrons are released from the surface of a heated metal.

The The prop proper ertities es of cath cathod odee ray rays (i) (ii) (iii)

3.

They travel in straight lines. They are fast moving electrons and therefore can generate energy when they hit the fluorescent screen. They are deflected by electric and magnetic fields and are negatively charged.

The diagram shows the structure of a simple cathode ray tube.

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Name:……………………………………………………. Electronics/Form 5

(a) Name Name the compo compone nents nts labe labeled led P, P, Q, R, S and T. Component P Q R S

Name of the components filament cathode anode X-plate

T

Y-plate

Function of the components To heat up the cathode Emit electrons Receive electrons Deflect electron beam horizontally Deflect electron beam vertically

(b) The CRO can be used to : i. display wave forms ii. measure potential difference of DC and AC supply iii. measure a short time interval 4.

The figure figure bel below ow show showss a trace trace form formed ed on the screen screen of a CRO. CRO.

If the Y-gain control on the CRO is set at 0.5 V cm -1 and the time-base is set at 5 ms cm-1. Find the peak voltage V P , Period, T and Frequency, f. peak voltage V P

Period, T

Peak voltage, V P

Period, T = 4 x (5 x 10 -3)

= 1.5 cm X 0.5 V = 0.75 V

Frequency, f. -2

= 2.0 X 10 s


frequency, frequency, f = 1/T = 1/0.02 = 50 Hz

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5.

If the same same the time draw a now be

4.2 Understanding semiconductor diodes.

signal signal is appli applied ed to the CRO but base is readjusted to 10 ms/cm, sketch to show the trace that will formed on the screen?

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A student is able to : Describe semiconductors semiconductors in terms of resistance and free electrons Describe n-type and p-type semiconductors. • Describe semiconductor diodes and their function. • Describe the use of diodes as rectifiers. use of a capacitor capacitor to smooth the output current and output voltage voltage from a • Describe the use rectifier circuit. • •

1.

(a) (a) A semi semico cond nduc ucto torr is a mat mater eria iall whos whosee resi resist stan ance ce is is betw betwee eenn the the resi resist stan ance ce of of a conductor and an insulator .

(b) Doping is a process when small amounts of impurities are added to pure semiconductors semiconductors causing an increase in the conductivity of the material. (c) A p-type p-type semicondu semiconductor ctor is produc produced ed when when a semicondu semiconductor ctor materia materiall such as germanium/silicon is doped with a trivalent element like boron/indium/gallium. (d) A n-type n-type semicondu semiconductor ctor is produc produced ed when when a semicondu semiconductor ctor materia materiall such as germanium/silicon germanium/silicon is doped with a pentavalent element like arsenic/antimony/phosphorus.

.

(e) A semiconductor diode is a p-n junction diode where the p-type material is


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Name:……………………………………………………. Electronics/Form 5 called the anode and the n-type material is called the cathode

(f)

In forward-biased a current flows through the diode but in reverse -biased current does not flow through the diode.

(g) Reverse-biased,

Bulb lights / does not light up

Anode

Cathode

Symbol of diode

2.

Diagra Diagram m 1 shows shows an elec electri tricc circui circuitt with one one diod diodee and the the trace trace prod produce ucedd is shown shown on on a CRO connected across the resistor R. Diagram 2 shows an electric circuit with four diodes and the trace produced is shown on a CRO connected across the resistor R.

(a)

Rectification is a process to convert an alternating current into a direct current by using a diode.

(b) (b)

Comp Compaaris rision ion betw betwee eenn : Diagram 1 Diagram 2 The diode is connected in series to the The diodes are connected in a quadrangle resistor R. with two junctions connected to the power supply and the other two junction across the resistor R. Diode is used as a half - wave rectifie fier

Diode aarre uussed aass a full - wave rectifier.


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Name:……………………………………………………. Electronics/Form 5 Both input are alternating current voltages and the outputs are direct curren cur rents ts .

(c)

Trace the path path ta taken ken bbyy the current current in Diagram.2 Diagram.2 if the terminal terminal X is positi positive. ve. Current flows from X → P → S → A → B → Q → R → Y

(d)

A capacitor is an electric component that needs to be connected to the output of both the circuits to produce a more constant output.

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4.3 Understanding transistors

A student is able to: t erminals.. • Describe a transistor in terms of its terminals • Describe how a transistor can be used as a current amplifier. • Describe how a transistor can be used as an automatic switch.

1. Name the two types of transistors as shown in Figure 4.31(a) 4.31(a) and 4.31(b) and label the three terminals X

collector base

Z

emitter Y

Figure 4.31 (a)

Type of transistor : p-n-p transistor

X

Y

Figure 4.31 (b)

Type of transistor : n-p-n transistor


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2. Transistor as a Current Amplfier Amplfier mA I

R 2

C

R 1 µA

IB

R

I E

A transistor can function as a current amplifier by allowing a small current to control a larger larger current. Rheostat R changes the the base current. A small change in the base current, IB will cause a big change in the collector current, IC. The current amplification can be calculated as follows: Current Amplification =

3.

∆ I C ∆ I B

The diagram diagram below below shows a circuit circuit which acts as an automatic automatic switch to turn on the motor M when the surroundings is dark.

(a) Name Name the comp compone onent nt labe labeled led P,Q P,Q and and S. Component P Q S

Name of the components Light Dependent Resistor Transistor Relay

(b) What is the the fun functio ctionn of the the compon component ent llabel abelled led R? R? To control the base current. WAJA physics © 2009 Hak Cipta Jabatan Pelajaran Perak

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(c) The figur figuree be below low shows shows how how the collector collector current, current, I c and the base current, I b flow.

(d) What happen happenss to the magnitu magnitude de of the the potential potential differ difference ence V S when the surroundings surroundings become bright? Tick ( √ ) the correct answer in the box provided Increase Decrease

√

(e) Explain Explain how how the chan change ge in the the potenti potential al differen difference, ce, V S, will cause the motor M to be turned on? As VS increases, the base current increases causing the collector current to increase by a large magnitude. This will cause the relay to complete the circuit and switch on the motor.


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4.4 Analysing logic gates

A student is able to: • Draw symbols for the following logic gates . i. ii.

• • •

AND OR N0T iii. iv. NAND v. NOR Build truth tables for logic gates in combination for a maximum of 2 inputs. State that logic gates are switching circuits in computers and other electronic systems. Describe applications applications of logic gates control systems.

1. Draw symbols for the following logic gates and state their action in a truth table i.

AND

ii.

OR

iii.

N0T

iv.

NAND

iv.

NOR

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2.

The figure below shows a circuit consisting of three different logic gates.

(a) (a) Name Name the the log logic ic gate gatess Logic gate P Q S

Name of the logic gate NOT AND OR

(b) Complete Complete the the truth truth ttable able for the the system system shown shown above. above. Input

(c) (c) (i) (i)

Output

A

B

0 0 1 1

0 1 0 1

0 1 1 0

The The comb combin inat atio ionn of the the logi logicc gate gatess abov abovee can can be rep repla lace cedd by a sin singl glee logi logicc gate gate.. What is this equivalent equivalent logic gate? NAND

(ii)

Give the Bool Boolean ean eequati quation on for for the logic logic gate gate in your answer answer in ( c)(i) c)(i) above above..


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3.

The circuit circuit below shows a logic circuit circuit used used in a cold room where where frozen meat is stored. The alarm will be turned on if the temperature of the cold room is too high. The buzzer will be turned OFF if the output logic is 0 and be turned ON if the output logic is 1.

(a) Name the llogic ogic gate used in the the circuit circuit above. above. NOT

(b) Based Based on the informatio informationn above, above, complete complete the truth table table for the logic logic gate above. above. Input 1 0

Output 0 1

Alarm OFF ON

(c) Name Name the the compo componen nentt labe labeled led E. Thermistor

(d) If the temperatu temperature re of the cold cold room increas increases, es, what happen happenss to the quantity quantity in the table table below? Complete the table with the appropriate answers. Resistance of E Current flowing flowing through the logic gate Condition of the alarm

Decrease Low ON


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Form 5 Physics Chapter 4 - Teacher's Copy

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