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YOUR PARTICIPATION FOR THE GROWTH OF PHYSICS REFERENCE BLOG

Monday, December 18, 2017

The following trace is seen on the screen of a cathode-ray oscilloscope. The setting of the time-base is then changed from 10 ms cm-1 to 20 ms cm-1 and the Y-plate sensitivity remains constant.



Question 7
The following trace is seen on the screen of a cathode-ray oscilloscope.
The setting of the time-base is then changed from 10 ms cm-1 to 20 ms cm-1 and the Y-plate sensitivity remains constant.

Which trace is now seen on the screen?







Reference: Past Exam Paper – June 2016 Paper 13 Q5





Solution:
Answer: C. 

The time-base setting affect the trace horizontally while the Y-plate sensitivity affects the trace vertically.

Initially, the time-base setting is 10 ms cm-1.

The period T occupies 4 cm.
Period T = 4 × 10 = 40 ms


The time-base setting is changed to 20 ms cm-1.

Even if the setting is changed, the period of the wave remains the same.
Period T = 40 ms


From the new setting, 1 cm represents 20 ms. The period will now be correspond to 2 cm. That is, in 2 cm, we can obtain a complete wave.


The Y-plate sensitivity has not been changed. So, the amplitude of the trace remains as it was initially.

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