Question 2
AIM: To determine the frequency of oscillation of an automobile windshield wiper with varying current.
- Connect the circuit as shown in Fig. 2.
- Fix the wiper arm and the wiper blade to the wiper motor.
- Close switch S.
- Read and record in Table 2 the:
(i) current flowing in the circuit;
(ii) number of complete oscillations per minute.
- Open switch S.
- Repeat steps (c) to (e) for the other values of resistor in Table 2.
- Plot a graph of number of complete oscillations on the vertical axis against the current flowing in the circuit on the horizontal axis.
- Determine the slope of the graph.
- Comment on your result.
- State two precautions taken in carrying out the experiment.
Table 2
Resistor (Ω) |
Current (A) |
Number of complete oscillations per minute |
20 |
|
|
40 |
|
|
60 |
|
|
80 |
|
|
100 |
|
|
Observation
Table 2
Resistor (Ω) |
Current (A) |
Number of complete oscillations per minute |
20 |
0.60 |
48 |
40 |
0.30 |
24 |
60 |
0.20 |
16 |
80 |
0.15 |
12 |
100 |
0.12 |
10 |
(h) Slope = Y2 – Y1
X2 – X1
40 – 20
0.5 – 0.25
= 20
0.25
:. Slope = 80 cycles/min/A.
(i) Comment on result
- The higher the resistance, the lower the current flowing in the circuitOR current flowing through the circuit is inversely proportional its resistance.
- The higher the resistance, the lower the number of complete oscillations/minute of the wiper motor and vice versa OR speed of the wiper motor is inversely proportional to the resistance of the circuit.
- The higher the current flowing through the circuit, the higher the number of complete oscillations/minute of the wiper motor and vice versa. OR The speed of the wiper motor is directly proportional to the current flowing through the circuit
(j) Precautions in carrying out the experiment
- I ensured tight connection
- I avoided error due to parallax in meter reading
- I repeated each step of experiment to reduce random errors
To obtain maximum mark, the graph is expected to be drawn with correct title, points of values, line of best fit, scales and labeling of axes units. Only a few candidates attempted this question.