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]
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