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.