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

4. ELECTRONICS [ ……/25 x 100 = % ]Instruction: Answer all questions in this section.

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 difference using the C.R.O. -- Measure short time intervals using the C.R.O. -- Display wave forms using the C.R.O. Solve problems based on the C.R.O. display

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

2. The properties of cathode rays

(i) They travel in straight lines.(ii) They are fast moving electrons and therefore can generate energy when they

hit the fluorescent screen.(iii) They are deflected by electric and magnetic fields and are negatively charged.

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

(a) Name the components labeled P, Q, R, S and T.

Component Name of the components Function of the componentsP filament To heat up the cathodeQ cathode Emit electronsR anode Receive electronsS X-plate Deflect electron beam

horizontallyT Y-plate Deflect electron beam

vertically

(b) The CRO can be used to :

WAJA physics © 2009 Hak Cipta Jabatan Pelajaran Perak 1

Name:……………………………………………………. Electronics/Form 5 i. display wave forms ii. measure potential difference of DC and AC supply iii. measure a short time interval

4. The figure below shows a trace formed on the screen of a 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 VP , Period, T and Frequency, f.

peak voltage VP Period, T Frequency, f.

Peak voltage, VP = 1.5 cm X 0.5 V = 0.75 V

Period, T = 4 x (5 x 10-3) = 2.0 X 10-2 s

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

5. If the same signal is applied to the CRO but the time base is readjusted to 10 ms/cm, draw a sketch to show the trace that will now be formed on the screen?

4.2 Understanding semiconductor diodes. [ ……/31 x 100 = ………% ]

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

A student is able to :

Describe 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. Describe the use of a capacitor to smooth the output current and output voltage from a

rectifier circuit.

1. (a) A semiconductor is a material whose resistance is between the resistance of a conductor and an insulator .

(b) Doping is a process when small amounts of impurities are added to pure semiconductors causing an increase in the conductivity of the material.

(c) A p-type semiconductor is produced when a semiconductor material such as germanium/silicon is doped with a trivalent element like boron/indium/gallium .

(d) A n-type semiconductor is produced when a semiconductor material such as 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 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. Diagram 1 shows an electric circuit with one diode and the trace produced is shown 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.

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

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

(b) Comparision between :Diagram 1 Diagram 2

The diode is connected in series to the resistor R.

The diodes are connected in a quadrangle with two junctions connected to the power supply and the other two junction across the resistor R.

Diode is used as a half - wave rectifier Diode are used as a full - wave rectifier.

Both input are alternating current voltages and the outputs are direct currents .

(c) Trace the path taken by the current in Diagram.2 if the terminal X is positive.

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.

4.3 Understanding transistors [……../18 x 100 = ……….%]

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X

Z

Y

Name:……………………………………………………. Electronics/Form 5A student is able to: 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) and 4.31(b) and label the three terminals

collector base

emitter

Figure 4.31 (a) Type of transistor : p-n-p transistor

Figure 4.31 (b) Type of transistor : n-p-n transistor

2. Transistor as a Current Amplfier

A transistor can function as a current amplifier by allowing a small current to

control a larger current. Rheostat R changes 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:

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X

Y

IC

IE

R1

R2

R IB

mA

A

Current Amplification

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

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

(a) Name the component labeled P,Q and S.

Component Name of the componentsP Light Dependent ResistorQ TransistorS Relay

(b) What is the function of the component labelled R?

To control the base current.

(c) The figure below shows how the collector current, Ic and the base current, Ib flow.

(d) What happens to the magnitude of the potential difference VS when the surroundings become bright?Tick ( √ ) the correct answer in the box provided

Increase √Decrease

(e) Explain how the change in the potential difference, VS, 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

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

motor.

4.4 Analysing logic gates [ ……./23 x 100 = ……..% ]

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

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

i. ANDii. ORiii. N0Tiv. NANDv. 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 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

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

(a) Name the logic gates

Logic gate Name of the logic gateP NOTQ ANDS OR

(b) Complete the truth table for the system shown above.

Input OutputA B0 0 0

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

0 1 11 0 11 1 0

(c) (i) The combination of the logic gates above can be replaced by a single logic gate. What is this equivalent logic gate?

NAND

(ii) Give the Boolean equation for the logic gate in your answer in ( c)(i) above.

3. The circuit below shows a logic circuit used in a cold room 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 logic gate used in the circuit above.

NOT

(b) Based on the information above, complete the truth table for the logic gate above.

Input Output Alarm1 0 OFF

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

0 1 ON

(c) Name the component labeled E.

Thermistor

(d) If the temperature of the cold room increases, what happens to the quantity in the table below? Complete the table with the appropriate answers.

Resistance of E DecreaseCurrent flowing through the logic gate LowCondition of the alarm ON

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