Question 1
Question 1
AIM: to investigate the property of potentiometer as a component used in radio receiver.
(a) Copy in Table 1, the resistor code and value of the 5kΩ ohms potentiometer e.g. A40K, B25K.
(b) Place the 5kΩ potentiometer such that the shaft points upwards and the terminals face is as shown in Fig 1.
(c) Place the probes of the multimeter on terminals 1 and 3. Read and record resistance r13 in table 1.
Table 1
Potentiometer value resistor Rp |
Resistor code & value |
R13(kΩ) |
Shaft turned midway clockwise |
Rs = R12 + R23(kΩ) |
|
R12(kΩ) |
R23(kΩ) |
||||
5 |
|
|
|||
10 |
|
|
|
|
|
50 |
|
|
|
|
|
100 |
|
|
|
|
|
(d) Turn the shaft of the potentiometer anticlockwise to the end.
(e) Turn the shaft to midway position, measure and record in Table 1 the resistance (R12) between terminals 1 and 2.
(f) With the shaft in the same position as in (e) measure and record in Table 1, the resistance (R23) between terminals 2 and 3.
(g) Repeat steps (a) to (f) for the other three potentiometers.
(h) Comment on the differences in values, if any between Rp and Rs.
(i) Join terminals 2 and 3 of the 10kΩ potentiometer as shown in Fig. 2.
(j) With the shaft still at the midway position, measure and record the resistance R14 between terminals 1 and 4.
R14 =__________________________________
(k) State two applications of potentiometer in a radio receiver.
______________________________________________________________________
(l) State two precautions taken for accuracy of results.
______________________________________________________________________
Observation
The expected response was:
Table 1
Potentiometer value resistor Rp |
Resistor code & value |
R13(kΩ) |
Shaft turned midway clockwise |
Rs = R12 + R23(kΩ) |
|
R12(kΩ) |
R23(kΩ) |
||||
5 |
B5K |
4.5 – 5.5 |
0.8 – 0.88 |
4.0 – 4.09 |
4.88 - 5.57 |
10 |
B10K |
8.9 – 11.0 |
1.5 – 1.59 |
7.2 - 8. 09 |
8.7 – 9.68 |
50 |
B50K |
45.5 – 55.5 |
39.3 – 40.0 |
7.8 – 8.3 |
47.5 – 47.8 |
100 |
B100K |
90 – 110 |
15.5 – 15.8 |
81.4 - 85 |
97.2 - 100.5 |
|
4 marks |
8 marks |
8 marks |
8marks |
4 marks |
(Note: Maximum allowance of 10% tolerance value allowed)
(h) Rs is less than Rp (deduce from the Table)
Comparism to be deduced from the Table according to value recorded in Rp and Rs
(j) R14 = Any value around R12 and R23
(k) Applications of a potentiometer in a radio receiver
- Volume control
- Linearity control
- Tone control
- Biasing circuit
- To change resistance value
(l) Precautions taken for accuracy of results
i. I ensured that the multimeter leads are in firm contact with the terminals of the potentiometer.
ii. I avoided parallax error.
iii. I ensured that the multimeter was set to the correct voltage range.
iv I ensured correct polarity of the multimeter while taken the readings.
The chief examiner reported that candidates performed well in this question in that they showed good skills in the use of the ohmmeter to measure resistance. Candidates also showed that they have basic knowledge of the use of potentiometer in radio receiver.