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### #1Vixus

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Posted 07 March 2006 - 08:46 PM

Is it just me or are some of the old exam questions worded in an annoying way? For example:

A wave has amplitude 0.04m, after some time it falls to 0.02m... by what factor has the Intensity of the wave changed compared to its initial value?

It's probably just me but I knew I was getting this question wrong as soon as I answered it.

Can someone also show me how to do 10b from paper 2002?
A car horn produces a 200Hz note. The horn is sounded when the car is travelling at 30ms away from the observer. What is the frequency heard by the observer?

### #2broughy

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Posted 09 March 2006 - 09:49 PM

QUOTE(Vixus @ Mar 7 2006, 08:46 PM)

Can someone also show me how to do 10b from paper 2002?
A car horn produces a 200Hz note. The horn is sounded when the car is travelling at 30ms away from the observer. What is the frequency heard by the observer?

is that not a pretty standard doppler effect question? thats just my initial thought from a glance at it, looks like a "plug in the numbers" (yes, thats a technical term ) job to me. i don't know the formlua off the top of my head, but it'll be in your notes?

edit: formula you want to use would be-

where f(obs) = observed frequency, f(s) = frequency of source, V = speed of sound, & V(s) = speed of source

this is in unit 3 though, so you might not have covered it yet?
when i'm dancin' with you,
tomorrow doesn't matter,
turn that music up,
till the windows start to shatter,
cos you're the only one who can get me on my feet,
& i can't even dance

No Tomorrow - Orson

### #3Vixus

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Posted 12 March 2006 - 03:49 PM

Yeah, I was trying to calculate the speed of sound instead of just assuming it was 340m/s.

Can you tell me the relationship between optical path difference and path difference for a ray which is sent into glass. Ray X is a reflection of the incident ray. Ray Y is a refracted internal reflection of the original refracted ray. So now X & Y travel parallel to each other.

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