More help regarding sinewave questions

[kiddog]

Hello all,

Just wondering if someone could help me with a few more questions .....

1).What is the frequency increase in octaves if a frequency is increased from 100 Hz to 25.6 kHz?

2).How many decades is to raise a frequency from 300 Hz to 3 MHz ?

3).A sinusoidal current has an average value of 7.5 Amps. Determine its r.m.s. value.

4).A sinusoidal waveform of 10 Volts r.m.s. passes through a voltage +5 Volts, 200 times in 2 seconds. Find its frequency.

Any help is greatly appreciated.

 

[albbg]

Questions are easy. I think you should try to solve your homeworks by yourself. Just two hints:

Each octave the frequency is doubled, then starting from a frequency fo, after N octaves you will have_
fN=fo*2^2

Each decade the frequency is multiplied by 10, then starting from fo
fN=fo*10^2

 

[kiddog]

Thank you very much. Is question 4 just a case of 200/2?, the question just seems to be confusing me... sorry for sounding dumb I'm just starting out so it's all new to me!

 

[albbg]

Sorry, but in my previous answer there are two typos:

fN=fo*2^N instead of fN=fo*2^2
fN=fo*10^N instead of fN=fo*10^2

About the frequency (question N. 4) you know the wave passes through the same value (5V) 200 times in 2 seconds. You have to find first if 5V are the peak value (amplitude) converting from RMS to peak. Then take into account there is only one peak each period; but for each period all other voltages are hit twice (the sinusoid increases, reach the peak, then decreases). If you draw a sketch you can figure out better.

 

[ads-ee]

For Q4 you could take a look at this.

Hmm, and look at , they must have taken the same class last year ;-)