Question

A cathode ray oscilloscope (CRO) is a device that converts electrical signals into an active graphical representation on a fluorescent screen. The x-axis is always the time axis, where the 1cm is equal to the present time scale called the time base. A sound wave is displayed on the screen of a cathode-ray oscilloscope. The time base of CRO is set at 2.5ms/cm. What is the frequency of the sound wave?
          

A. 50Hz
B. 100Hz
C. 200Hz
D. 400Hz

Answer 1

Hint: Cathode ray oscilloscope is known as CRO. It is used by the student while doing practical. You can see the waveforms of a diode or any device. By looking at waves, we can determine many terms and get many conclusions using output waves.

Complete step by step answer:
CRO works on electric voltage. Using CRO in the laboratory, we can determine the time, VPP, amplitude, and the type of wave frequency over a wide range.
As the signal covers 4 divisions at 2.5 ms/cm, therefore signal period will be:
$\mathrm{T}=4\times 2.5\times {\displaystyle \frac{{10}^{-3}\mathrm{s}}{\mathrm{c}\mathrm{m}}}\times 1\mathrm{c}\mathrm{m}=10\times {10}^{-3}\mathrm{s}={10}^{-2}\mathrm{s}=0.01\mathrm{s}$
Therefore frequency,
$\mathrm{T}={\displaystyle \frac{1}{\mathrm{f}}}$
Where T is the time period, and f represents frequency.
$\Rightarrow \mathrm{f}={\displaystyle \frac{1}{\mathrm{T}}}={\displaystyle \frac{1}{0.01}}=100\mathrm{H}\mathrm{z}$

Hence the correct option is (B).

Additional information:Ray in the oscilloscope, uses a bright spot, which results from striking a beam of electrons. This spot shows variation as the input varies. The common effect of a beam of an electron is used for obeying the changes in the instantaneous values of continuously changing input waves.

Note:To focus electron beams, we used two methods, electrostatic focusing, and electromagnetic focusing. Do not get confused between CRO and CRT. CRO stands for a cathode-ray oscilloscope while CRT stands for a cathode ray tube.