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Monday, February 4, 2019

A student is investigating an electrical signal using a cathode-ray oscilloscope (c.r.o).


Question 15
A student is investigating an electrical signal using a cathode-ray oscilloscope (c.r.o).

The frequency of the signal is 50 kHz.

Which time-base setting on the oscilloscope should be used?
A 50 ms cm-1                   B 1 ms cm-1                     C 10 μs cm-1                 D 0.5 μs cm-1





Reference: Past Exam Paper – March 2017 Paper 12 Q4





Solution:
Answer: C.

Frequency = 50 kHz = 50 × 103 Hz


On the screen of the c.r.o, the period of the signal can be found.

Frequency f = 1 / T

Period T = 1 / f = 1 / 50×103
Period T = 2.0×10-5 s = 20 × 10-6 s

Period T = 20 μs

The time-base setting should be such that a complete wave may be seen.


A and B are obviously incorrect.

If the time-base setting is 10 μs cm-1, one complete wave may be observed within 2 cm.
 
If the time-base setting is 0.5 μs cm-1, one complete wave may be observed within 20 cm. The screen of the c.r.o is smaller than 20 cm. So, a complete wave cannot be seen on the screen. [D is incorrect]

1 comment:

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