Carmel Holy Word Secondary School Advanced physics TAS laboratory menu.

Experiment 10 : The transistor as a linear voltage amplifier.

Name : Class : ()Group :

Preliminary questions

1.For a transistor used as an amplifier, which mode should it be?

2.State the meaning of anti-phase.

3.For a current containing both a.c. and d.c., which component would pass through a capacitor?

Name : Class : ()Group :

Experiment 10 : The transistor as a linear voltage amplifier.

Objective

Investigate the d.c. and a.c. voltage amplifying power of a transistor.

Apparatus

1.n-p-n transistor (1)

2.5 kΩvariable resistor (2)

3.15 kΩresistor (1)

4.1 kΩresistor (1)

5.2.2μF capacitors (2)

6.voltmeters (100 μA base meter and 1 V, 5 V and 10 V multipliers) (2)

7.signal generator (1)

8.oscilloscope with dual trace (1)

9.6.4 V battery (1)

Experiment 1 : The input/output characteristics of a transistor

Setup

Procedures

1.Connect the circuit as shown above.

2.Gradually vary the potentiometer. Record the readings (Vin and Vout) in both the voltmeters in Table 1.

Precautions

1.Check the operation of the potentiometer with a voltmeter before connecting the circuit.

2.Pay attention to the polarities of the power supplies and the meters.

3.Before the start of the experiment, set the potentiometer to give zero volt.

Data

Vin( )
Vout ( )
Vin( )
Vout ( )

Table 1Teacher’s signature :

Calculations and graphs

1.Plot Vout against Vin as Graph 1.

Experiment 2 : The input/output characteristics of a transistor

Setup

Procedures

1.Connect the circuit as shown above.

2.Set the CRO for measuring voltage and to display d.c. waveforms. Both the transistor and the signal generator are powered off. Seek approval from your teacher before you proceed.

3.Power on the transistor first. Change the potentiometer until the output at Y2 is 3 V. Sketch the CRO displays both before and after powering on the transistor on Figure 1, state the voltage gain setting of Y2.

4.Turn on the signal generator. Set the frequency to 1 000 Hz. Increase its voltage output gradually. Make sure the output waveform is undistorted. Sketch the CRO display on Figure 2.

5.Connect the terminal Q of the transistor module with the Y2-input of the CRO. Notes the changes to the waveform.

6.Measure the amplitudes of the input ΔVin and output ΔVout waveforms. Record the results in Table 2.

7.Repeat precedure 6 with four different amplitudes of input signals. Make sure the output is still undistorted. Hence, find the voltage gain of the transistor.

8.Increase the output of the signal generator until distortion is observed. Sketch the distorted waveform displayed on the CRO on Figure 3.

9.Restore the output to be undistorted. Change the potentiometer until only the lower half of the output waveform is displayed. Sketch the result of the CRO display on Figure 4. Have you decreased or increased the output of the potentiometer?

10.Repeat step 9 so that only the upper half of the output waveform is displayed.

Precautions

1.When using the dual trace CRO to display waveform, note the followings:

1.1Adjust the voltage gain and the time base such that more than one complete waveform may be seen.

1.2Turn the trigger source to “INT” or “CH1” and the trigger mode to “AUTO”. Change the trigger level until a stable waveform is displayed.

1.3Turn the AC/DC switch to “DC”.

1.4Turn the y-variable to “CALD” position.

2.In procedure 4, use very small output of the signal generator. Increase the sensitivity of the CRO if no significant change in the waveform is observed.

3.In procedure 6, set both y-variables to “CALD” position.

Data

Figure 1 Figure 2 Figure 3 Figure 4

Voltage gain setting of Y2 in procedure 2.

In procedure 5, what happens to the waveform when switched to use N?

ΔVin ( )
ΔVout ( )
Voltage gain

Table 2Teacher’s signature :

Average value of voltage gain.

In procedure 9, is the output voltage of the potentiometer decreased or increased?

In procedure 10, is the output voltage of the potentiometer decreased or increased?

Discussion

1.By using , find the current amplification factor of the transistor.

2.An a.c. voltage can also be increased by a step-up transformer, explain why we do not use it?

3.At the input, the a.c. signal is applied via a capacitor. Explain it.

4.State the purpose of the capacitor at the output terminal N.

5.State the limitation of the linear voltage amplifier using a transistor.

Conclusion

1/5

HKAL Physics TAS lab menu 10