Chapter 4 Form 5 Physics

8/11/2019 Chapter 4 Form 5 Physics

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Physics Module Form 5 Chapter 4- Electronics GCKL 2010

4-2

2. Fill in the blank all components and its functions.

Figure 9.3


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4-3

What is the

energy change?

eVchangeEnergyPotential

The principle of conservation of energy is the change of____________electric energy to________

energy.

eVmv 2

2

1,

How to measure

voltage?

How to measure

short time

intervals?

To measure a D.C voltage:

The unknown voltage, V= (Y-gain) h

To measure a A.C voltage:

Peak-to-peak voltage,Vpp = (Y-gains) h

Peak voltage, Vp= (Y-gains)2

1 (h)

Short time intervals, t= no. of divisions between two pulses time-base value.

Examples

1. The diagram shows the trace on the screen of a CRO when an a.c voltage is connected to the

Y-input. The Y-gain control is set at 2 V/div and the time base is off.

Calculate the value of :

(a) Peak-to-peak voltage,Vpp

(b)Peak voltage, Vp.

Solution:

2. An ultrasound signal is transmitted vertically down to the sea bed. Transmitted and reflected

signals are input into an oscilloscope with a time base setting of 150 ms cm-1. The diagram

shows the trace of the two signals on the screen of the oscilloscope. The speed of sound in

water is 1200 ms-1. What is the depth of the sea?

Solution:

2

2

1changeEnergyKinetic mv

Figure 9.11


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4.2 UNDERSTANDING SEMICONDUCTOR DIODES

What is

semiconductor? It is .................................

............................................................................................

What is the

doping

process?

What is

semiconductors

diodes?

1. Fill in the blank for the statement below.

(a) n-type semiconductor

Silicon like Silicon doped with atoms such as or phosphorus. The

phosphorus atoms have ..valence electrons. The fifth electronis freeto move through

the silicon. The silicon has ... as majoritycharge-carriers and it thus

known as an n-type semiconductor.

(b)p-type semiconductors

Semiconductor like Silicon doped with .. atomssuch as or indium

hasmore positive holes. The Boron atoms have only .valence electronswith

missing an electron. The majority charge-carriers in this semiconductor are the

..................... and this semiconductor known as a p-type semiconductor.


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What is the

function of

diodes?

Semiconductor Diode

A diode is a component (device) that allows _______________to flow in________direction only.

A diode acts like a one-way valve to electric current.

The following figure shows structure and the symbol of a semiconductor diode :

Draw the symbol for a semiconductor diode.

How does the p-n junction diode work?

Any further movement of_____________across the boundary in the depletion layer will be repelled

by the charges in the layer.

The layer of the negative charge in the p-type region will prevent the majority charge carriers from the

__________region(the electrons) from crossing the boundary. Similarly , the positive charge layer inthe n-type region will prevent the majority charge carriers from the__________region(the holes) from

crossing the boundary in the opposite direction.


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Thus, a potential difference ,known as the___________.In its normal state a p-n junction delivers no

____________ since the charges are in equilibrium. The effect of this junction voltage is to_________

charge carriers from drifting across the junction.

What is the use

of diodes asrectifiers?

What is the use

of a capacitor in

a rectifier

circuit?

Diode as a Rectifier

A diode can act as a rectifier because it can convert _______________into_________________

The process of converting a.c. to d.c. is called_______________.

There are two types of rectification process :

(1) _____________rectification

(2) _______ - wave rectification

Half- wave rectification

For half of the cycle, A is more positive than B ,the diode conducts.

For the other half cycle, A is more negative than B , nocurrent can flow.

Full-wave rectification

For half of the cycle, A is more positive than B ,the diode D1 and D3___________and the

___________flows through the resistance.

For the other half cycle, A is more negative than B , the diodes D2 and D4 conduct and current flows

through the resistance in the same direction as before.

In the circuit above, using arrows to draw the flow of current.

Capacitor

A capacitor is device which can

(1) __________ electric __________

(2) ____________out waveform in the rectified output

(3) separate the________and d.c (as a filter)


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Smoothing output wave by a capacitor

By connecting a capacitor parallel to the resistance , the half-wave and the full-wave rectified

waveform could be partially_____________out.

Label the output below.

For half of the cycle, the capacitor is charged up.___________is stored in the capacitor.

For the other half cycle, the capacitor_________ its__________(discharges)

So the capacitor can produced a steady output or output is stabilised.

UNDERSTANDING TRANSISTORS


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4.3

What is the type

of transistors?

1. Draw and label the symbol of n-p-n transistor and p-n-p transistor.

Transistor as an Automatic Switch.

1. Complete the statement below.

The circuit shown in figure, a resistor, RXand a . are being used to

form a potential divider. If the variable resistoris set tozero, the base voltage is . and

the transistor switches . If the resistance of the variable resistor is increased, the base

voltage will. When the base voltage reached a certain minimum value, the base

current,IBswitches on the transistor. A large collector current,ICflows to light up the bulb.

2. State the transistor used in this circuit.

3. Light Controlled Switch

(i) Complete the statement below.

IC

IE

IB

RX

RYBase

Battery

Figure 9.23

IC

IE

1k

R

LDR

10 k

6 V

Figure 9.24


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The ...... (LDR) has a very high resistance in the . and a low

resistor in ... R is a fixed . The LDR and R form a potential divider

in the circuit. Voltage across the LDR is enough to switch on the transistor and thus

lights up the ............. automatically at .................

In bright light, the LDR has a very . ................... compared to R. Then, the base voltage

of the transistor is too .. to switch on the transistor.

(ii) Complete the table below.

Condition RLDR VLDR Transistor (ON or OFF)

Daylight

Darkness

Remember Ic>>>>Ib

9.2.4 Transistor as a Current Amplfier

1. Complete the statement below.

A transistor functions as a current amplifier by allowing a small current to control a larger

current. ., ICis primarily determined by the .., IB. A

.. change in the base current, IBwill cause a .. change in the collector current, IC.

The current amplification can be calculated as follows:

2. What will happened to the readings of the miliammeter, mAand microammeter, Awhen theresistance of R is reduced?

IC

IE

R1

R2

R IB

mA

A

Current Amplification

B

C

I

I

.

Figure 9.25


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ANALYSING LOGIC GATES

What is logic

gate?

A circuit that has one or more input signals but only one output signal and is applied in a computer

and other electronic devices. This gates use in switching on and off operations.

Each input and output can be either high (logic 1) or low (logic 0).

Binary 0 represents 0 V and a binary 1 represents a non zero voltage.

What is the

combination of

the logic gate?

1. Complete the table below.

Gates Symbol Truth table

AND gate

Output is ON only when

both input A and B are

switch ON.

Input Output

A B Y

OR gate Output is ON when either

one of inputs or both is ON.

Input Output

A B Y

NOT gate

Output is ON when input is

OFF and vice versa.

Input Output

A Y

4. 4


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NAND

gate

It output is OFF when both

inputs are both ON.

Input Output

A B Y

NOR gate

Output is ON when both

input are OFF.

Input Output

A B Y

What is the

application of

logic gate

control

systems?

1. Diagram shows a simple electronic control system that is used as an automatic and manual

switches to switch on the street lights when it is dark. The control system allows the street

lights either to switch on manually by a switch at any time, or automatically by a light sensor

when it is dark. Light sensor : daytime =1 Dark/ night = 0

Switch on = 1

Switch off = 0

Switch

A

Light sensor

B

Output

ofinverter, C

Output

Street light on = 1

Street light off = 0


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2. A student would like to construct a logic gate circuit to switch on an air conditioner in his

home automatically. He has chosen a light-sensitive device to detect daytime and night and

a heatsensitive device to detect the surrounding temperature. He has constructed a truth

table to show the function of the logic gate circuit to switch on the conditioner. Draw the

logic gate circuit that will switch on the air conditioner based on the function stated in the

truth table.

Input P Input Q Output R

Night =0 Cold = 0 Off = 0

Night =0 Hot = 1 On = 1

Day=1 Cold = 0 On = 1

Day=1 Hot = 1 On = 1

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

(a) Name the logic gates

Logic gate Name of the logic gate

P

Q

R

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

Input Output

A B

0 0

0 1


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1 0

1 1

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

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

4.

Input Output

A B P Q Y


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Check Yourself 11. Which of the following is a method to produce cathode ray?

A. Heat a metal filament.

B. Magnetise a metal plate in vacuum.

C. Incident light on the surface of a metal.

D. Bombard a metal with high speed particles.

2. What is the function of the electron gun in a cathode ray oscilloscope?

A. To deflect the electron beam.

B. To produce a narrow beam of electrons.

C. To ionise the air molecules.

D. To shoot the electrons in all the directions.

3. Which of the following quantities cannot be measured by the cathode ray oscilloscope?

A. The speed of sound wave in air.

B. The potential difference across a resistor.C. The electric current in a conductor.

D. The short time interval between two hand claps.

4. In a pure semiconductors

A. There are more free electrons than holes.

B. There are equal numbers of free electrons and holes.

C. There are more holes than free electrons.

D. The resistance increases with temperature.

5. In a p-type semiconductor

A. The number of holes is less than the number of free electrons.

B. The number of holes is equal to the number of free electrons.

C. The number of holes is more than the number of free electrons.

6. Which of the following concerning cathode ray is true?

A. It is light rays from hot filament.

B. It consists of positively charged particles.

C. It can be deflected by a magnetic field.

D. It is a radiation from nuclear decay.

7. Figureshows the trace on the screen of a C.R.O. with its Y-gain control adjusted at 5 V/ div.

What is the peak value of the voltage measured?

A. 5.0 V B. 10.0 V C. 12.5 V D. 20.0 V

8. Which of the following is not a characteristics of a diode?A. It only allows electricity to flow through it in one direction.

B. It is formed by joining a p-type and an n-type semiconductor together.


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C. emitter, collector and base

D. emitter, collector and Earth

13.When an A.C. signal is connected to the input terminals of a C.R.O., the trace shown on the

screen is as shown in Figure. The time-base of the C.R.O. is set at 4 ms?cm. What is the

frequency of the A.C. signal?

A. 27.8 Hz B. 36 Hz C. 62.5 Hz D 83.3 Hz

14.Which of the following is not true about an n-type semiconductor ?

A. It is formed by adding pentavalent impurities.

B. It has more holes than free electrons.C. Its majority charged carriers are electrons.

D. Its minority charged carriers are holes.

15.

The function of the capacitor in fhe figure above as

A a rectifier B an amplifier

C a current filter D a voltage smoother

16.one of the uses of semiconductors is to make of a transistors. In an npn transistor, two types of

semiconductors are used to make the electrodes. Which of the following combination below is

the correct sequence of the semiconductors used?

Emitter collector base

A. p-type n-type n-type

B. n-type n-type p-type

C. n-type p-type n-type

D. p-type p-type n-type

Structures

1. The diagram shows a waveform obtained from an a.c. power supply connected to Y-input of a

CRO.

(a) What is


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(i) the frequency of the current?

(i) the peak voltage of the current?

(b) Draw the waveform display on the screen of the CRO in figure below when

(i) the time-base switch is off.

(ii) the time-base switch is on and the

a.c. power supply is replaced by a d.c. generator.

ssay

1 (a) Figure shows a light bulb connected to a resistor R, two switches A and B and a LED.

The states of the switches A and B determine whether the LED emits light or not. The circuit

represents a logic gate.

(i)

What is a logic gate?


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(ii) Write down the states of the switches A and B when the LED is switched on and the states of

A and B when the LED is switched off. Construct a truth table to show the state of A and B

for the effect on the LED. Hence name the logic gate that produces a similar truth table

and draw the symbol of the logic gate.

A B LED

(c) Figure below shows the combination of two logic gates, X, to form a single logic gate.

(i) Name the logic gate X.

(ii)Complete the truth table given in Table belowP

Q R S

Chapter 4 Form 5 Physics

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