Physics Q's Help!! (1 Viewer)

[x.Exhaust.x]

I need help with the question below. Physics half yearly tomorrow as well... :burn: Explain how you answered them because this is the only question I'm confused with, and it's the 1st question in the sheet...

Students sitting on a wharf measure the wavelength of some passing waves at 3.0m. They find that four waves pass in 6.0s.

a) Calculate the period of the waves
b) Calculate the frequency of the waves
c) Calculate the speed of the waves

Use Velocity = Frequency x Wavelength

And would anyone happen to have questions of Snell's Law. I know the formula but I'm still not so sure about the formula. In the law, one of them changes from v1/v2 to v2/v1. So confused...

Thanks.

 

[Continuum]

Explain how you answered them because this is the only question I'm confused with, and it's the 1st question in the sheet...

Students sitting on a wharf measure the wavelength of some passing waves at 3.0m. They find that four waves pass in 6.0s.

a) Calculate the period of the waves

The period of a wave is basically how long it takes for one complete wave to pass you. There are four waves in 6 seconds, so each wave would take 6/4 seconds to pass. Thus, the answer is 1.5 seconds.

b) Calculate the frequency of the waves

The frequency of the waves is how many waves pass in a 1 second time frame. You use the 'f=1/P' rule here, where 'f' is frequency and 'P' is period. We already figured out the period of the wave in the question before (1.5 seconds), so the frequency would simply be 1/1.5. Thus, the answer is 2/3 Hz (the unit of measurement for frequency).

c) Calculate the speed of the waves

We use the rule 'v=f x wavelength' here. We already know its frequency (2/3Hz) and the wavelength (3m, as given in question), so we just times 2/3 and 3 together. Thus the answer is 2m/s.

Good luck.

 

[x.Exhaust.x]

Thanks a lot continuum. One last question.

I know that for sin i / sin r = constant, but sometimes it switches to sin r / sin i (a reciprocal). Why is that? Only part I'm confused with.

Thanks.

 

[Continuum]

Snell's law doesn't equal to a constant though... it states that:

sini/sinr = nr/ni = vi/vr (n is the refractive index and v is the velocity)

Thus, when you switch it from sini/sinr to sinr/sini, you must also switch the other fractions around. Maybe you're talking about the refractive index of air, because 1/1.0...x would be no different from 1.0...x/1.

I'm doing this from memory, so you should check everything I said with other people as well.

 

[Aerath]

Sometimes, it depends on what you're trying to find. I prefer to have what I'm trying to find in the top left hand corner. That's why I'd have it as a reciprocal.

 

[x.Exhaust.x]

Thanks guys. I don't think the exam went so well. I memorised my 'theory' dotpoints and they went well. But when the practicals came, especially graphing (60% of the whole paper was practicals I believe :burn: ), it didn't go so well.

Oh well can't change the past...