6.1 State TWO categories of amplifiers. 6.2 Refer to FIGURE 6.2 and answer the questions that follow. 6.2.1 Determine the maximum voltage across the collector terminal of the transistor. 6.2.2 Calculate the maximum collector current in FIGURE 6.2. 6.2.3 Draw the load line for the characteristics of FIGURE 6.2 on ANSWER SHEET 6.2.3. 6.2.4 Indicate this point on the load line on ANSWER SHEET 6.2.3. 6.2.5 Determine the value of the collector current as the class A bias point. 6.3 Refer to FIGURE 6.3 and answer the questions that follow. 6.3.1 State the function of R1 and R2. 6.3.2 Explain why the values of the coupling capacitors are purposely selected to be as large as possible. 6.3.3 State the purpose of Re. 6.3.4 Describe the RC coupling. 6.4 Refer to FIGURE 6.4 and answer the questions that follow. 6.4.1 State ONE specification of the transformer-coupled amplifier. 6.4.2 State TWO advantages of the circuit in FIGURE 6.4. 6.4.3 Name TWO devices, apart from the speaker, that can be connected across the terminals of transformer T2. 6.5 FIGURE 6.5 below represent the radio-frequency amplifier. Answer the questions that follow. 6.5.1 State ONE purpose of Ce. 6.5.2 Describe the functions of the radio-frequency amplifier. 6.5.3 Explain why variable pre-set capacitors C1 and C2 have been used with transformer T2. 6.6 Refer to FIGURE 6.6 and answer the questions that follow. 6.6.1 Describe what would occur when switch S is moved to position 2. 6.6.2 Draw the voltage waveform across the capacitor on the ANSWER SHEET OF QUESTION 6.6.2 after the switch is moved to position 2. 6.6.3 State how the frequency of this tank circuit can be increased. 6.7 Study FIGURE 6.7 and answer the questions that follow. 6.7.1 State ONE application of the Hartley oscillator. 6.7.2 State the function of C1 and C2. 6.7.3 Describe how the state of oscillation can be maintained. 6.8 Refer to FIGURE 6.8 and answer the questions that follow. 6.8.1 State ONE function of transistor Q4. 6.8.2 Describe how the frequency of the oscillator in FIGURE 6.8 can be adjusted, if the value of the resistors are kept the same. 6.8.3 Compare the feedback used in transistor amplifiers to oscillator circuits. 6.9 State the difference between LC and RC oscillators with reference to frequency.

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6.1 State TWO categories of amplifiers - NSC Electrical Technology Electronics - Question 6 - 2022 - Paper 1

Question 6

6.1 State TWO categories of amplifiers. 6.2 Refer to FIGURE 6.2 and answer the questions that follow. 6.2.1 Determine the maximum voltage across the collector term... show full transcript

Worked Solution & Example Answer:6.1 State TWO categories of amplifiers - NSC Electrical Technology Electronics - Question 6 - 2022 - Paper 1

Step 1

State TWO categories of amplifiers.

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Answer

Small signal amplifiers / Audio amplifiers.
Power amplifiers / Large signal amplifiers.

Step 2

Determine the maximum voltage across the collector terminal of the transistor.

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Answer

The maximum voltage across the collector terminal is measured to be 20 V.

Step 3

Calculate the maximum collector current in FIGURE 6.2.

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To calculate the maximum collector current, we can use the formula:

$I_C = \frac{V_{CE}}{R_C}$

Substituting the values:

$V_{CE} = 20 V$
$R_C = 3.33 \times 10^6 \Omega$

The maximum collector current, therefore, is:

$I_C = \frac{20}{3.33 \times 10^6} = 6 \, mA$ .

Step 4

Draw the load line for the characteristics of FIGURE 6.2 on ANSWER SHEET 6.2.3.

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Refer to ANSWER SHEET 6.2.3 for the drawn load line based on the characteristics provided in FIGURE 6.2.

Step 5

Indicate this point on the load line on ANSWER SHEET 6.2.3.

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Answer

Refer to the indicated point on the drawn load line in ANSWER SHEET 6.2.3.

Step 6

Determine the value of the collector current as the class A bias point.

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Answer

The value of the collector current at the class A bias point is determined to be 3 mA.

Step 7

State the function of R1 and R2.

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Resistors R1 and R2 are voltage dividers which set the voltage across the base emitter junction ( $V_{be}$ ) to 0.7 V to bias Q1.

Step 8

Explain why the values of the coupling capacitors are purposely selected to be as large as possible.

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The values of the coupling capacitors are made large to handle the wide range of frequencies, allowing signals to pass without significant attenuation.

Step 9

State the purpose of Re.

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The purpose of Re is for stabilization and to prevent thermal runaway in the transistor circuit.

Step 10

Describe the RC coupling.

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RC coupling allows each stage to maintain its own DC stability, which prevents DC interference from neighboring stages, providing effective signal coupling.

Step 11

State ONE specification of the transformer-coupled amplifier.

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The transformer-coupled amplifier can be used in circuits that require large current outputs.

Step 12

State TWO advantages of the circuit in FIGURE 6.4.

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It provides excellent impedance matching.
It enables efficient signal transfer between stages.

Step 13

Name TWO devices, apart from the speaker, that can be connected across the terminals of transformer T2.

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AC relay.
AC motor.

Step 14

State ONE purpose of Ce.

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Ce serves to provide an AC path to ground, thus avoiding any signal degeneration.

Step 15

Describe the functions of the radio-frequency amplifier.

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The radio-frequency amplifier selects the required signal frequency and provides amplification before passing it on to the mixer stage.

Step 16

Explain why variable pre-set capacitors C1 and C2 have been used with transformer T2.

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C1 and C2 are used to tune the tank circuit to the desired frequency, while blocking any DC current.

Step 17

Describe what would occur when switch S is moved to position 2.

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When the switch is moved to position 2, the capacitor will discharge, storing charges as electromagnetic fields in the inductor.

Step 18

Draw the voltage waveform across the capacitor on the ANSWER SHEET OF QUESTION 6.6.2 after the switch is moved to position 2.

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Refer to the drawn voltage waveform in ANSWER SHEET OF QUESTION 6.6.2.

Step 19

State how the frequency of this tank circuit can be increased.

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The frequency of oscillations can be increased by decreasing the value of either L or C in the tank circuit.

Step 20

State ONE application of the Hartley oscillator.

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The Hartley oscillator is used as a local oscillator in radio receivers.

Step 21

State the function of C1 and C2.

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C1 and C2 pass AC frequency to the tank circuit while blocking any DC component.

Step 22

Describe how the state of oscillation can be maintained.

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The state of oscillation is maintained through positive feedback from the collector to the tank circuit.

Step 23

State ONE function of transistor Q4.

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Transistor Q4 creates a 180° phase shift to ensure that the overall base maintains oscillation.

Step 24

Describe how the frequency of the oscillator in FIGURE 6.8 can be adjusted, if the value of the resistors are kept the same.

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The frequency of the oscillator can be adjusted by changing the values of the feedback capacitors.

Step 25

Compare the feedback used in transistor amplifiers to oscillator circuits.

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Answer

Oscillator circuits use positive feedback to sustain oscillations, while transistor amplifiers typically use negative feedback.

Step 26

State the difference between LC and RC oscillators with reference to frequency.

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Answer

LC oscillators generate high frequency signals while RC oscillators generate low frequency signals.

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