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Wednesday, July 12, 2017

A cathode-ray oscilloscope (c.r.o.) is connected to an alternating voltage. The following trace is produced on the screen. ...





Question 1
A cathode-ray oscilloscope (c.r.o.) is connected to an alternating voltage. The following trace is produced on the screen.


The oscilloscope time-base setting is 0.5 ms cm-1 and the Y-plate sensitivity is 2 V cm-1.
Which statement about the alternating voltage is correct?
A The amplitude is 3.5 cm.
B The frequency is 0.5 kHz.
C The period is 1 ms.
D The wavelength is 4 cm.





Reference: Past Exam Paper – June 2014 Paper 12 Q3





Solution 1:
Answer: B.

Amplitude is the maximum voltage. It can be obtained by considering the vertical position of the trace from the central line on the screen.
Y-plate sensitivity = 2V cm-1
Amplitude = 3.5 cm = 3.5 × 2 = 7 V
[A is incorrect]

Frequency = 1 / period = 1 / T
A value of time (not ‘wavelength’) can be obtained horizontally. [D is incorrect]
Time-base setting = 0.5 ms cm-1
Period T = 4 cm = 4 × 0.5 = 2 ms       [C is incorrect]
Frequency = 1/T = 1 / (2×10-3) = 0.5 kHz

10 comments:

  1. In Q1, the wavelength is also correct i.e 4cm Then why Option ?

    ReplyDelete
  2. In Q1
    Why D is incorrect. The wavelength is 4cm.

    ReplyDelete
    Replies
    1. The wavelength is NOT 4cm.
      THe horizontal axis on the CRO gives the time (on the distance).

      Wavelength is in metre while time is in second.

      Also, it does not even give the period directly. On a cro we need to use the time-base setting as shown above.

      Delete
  3. Thanks so much for this site!

    ReplyDelete
  4. Why cant the answer be A the amplitude is 3.5 cm

    ReplyDelete
    Replies
    1. the y-sensitivity is 2V / cm
      that is,
      1 cm -> 2V
      3.5 cm -> 3.5 x 2 = 7 V

      the amplitude is 7V

      Delete
  5. Replies
    1. the time-base setting is in millisecond/cm (ms/cm). we need to convert to SI unit (which is second)

      Delete

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