Oscilloscope calculations

1. Oct 30, 2016

eehelp150

1. The problem statement, all variables and given/known data
V1 = 10cos(10^4t)
V2 = 5cos(10^4t + pi/3)
Time Base setting = 0.1msec/div

By how many divisions will these two traces differ?
2. Relevant equations
W = 2pi/T

3. The attempt at a solution
W = 2pi/T
T = 2pi/W
W = 10^4
T = 0.628 milliseconds
0.628milliseconds/(0.1msec/div) = 6.28 divisions
Would the difference between 10cos and 5cos add a factor of 2 or 1/2 to the # of divisions?

2. Oct 31, 2016

CWatters

No. The 10 and 5 give you the amplitude. For example at a peak, when cos(...) =1, one waveform has the value 10 and the other 5.

Hints:

a) Both waveforms have a common 104t term. What does that mean?
b) One also has another term pi/3. What does that represent?

3. Oct 31, 2016

Staff: Mentor

You are making this difficult for yourself if you are attempting to answer this question without first sketching how the oscilloscope is displaying these two signals.

If you think you don't need to sketch this, then I say you most certainly do need to‼‼

4. Oct 31, 2016

eehelp150

a. Same frequency
b. Phase shift

5. Oct 31, 2016

CWatters

Correct.

Which of a and b shifts the trace left to right along the time axis relative to the other?

6. Oct 31, 2016

eehelp150

B would shift the graph over to the right by pi/3?

7. Oct 31, 2016

CWatters

Correct.

Although I think V2 would be shifted left relative to V1.

8. Oct 31, 2016

eehelp150

So how many divisions will these two traces differ?

Pi/3 divisions?

9. Oct 31, 2016

Staff: Mentor

You have calculated the period of the signals (the time for one cycle). How much of one period does the phase angle represent? What is it in milliseconds?

10. Oct 31, 2016

eehelp150

1/3 of the period?
0.209 ms?

11. Nov 1, 2016

Staff: Mentor

Can you show how you determined the 1/3 value? Is pi/3 really 1/3 of a full circle?

12. Nov 1, 2016

eehelp150

Pi/3 is 1/6 of the total period, so would it be 0.105ms or 1.05 divisions?

13. Nov 1, 2016

Staff: Mentor

That looks better!