Help Please .. Physics Question

[7amwakingupinthemorning]

Can someone please tell me how we could find the frequency of a wave using a cathode ray oscilloscope???

And tell me how the the answer to Question 5 in http://www.xtremepapers.me/Edexcel/Advanced%20Level/Physics/2010%20Jan/Edexcel%20Physics%20Unit%202%206PH02%20January%202010%20QP.pdf  (January 2010) is 50 ??   


Thanks xx

[Malak]

For Q5: Yes it is 50 Hz
Just telling you why, if ur not sure..

It says that one square is 5 ms, so you count squares for one wavelength i.e 4 squares so it takes 20 ms for a complete wave.
Now you know that this is the period 'T'
And frequency is 1/T , so 1/ 0.02 (20 changed to s)
That will give you 50