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Physics: Post your doubts here!

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Ahmed H. Al-Neel said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w07_qp_1.pdf
question 25 please!
Click to expand...
25)
Use dsinθ = nλ
So given, θ = 45 and n = 3
so d x sin45 = 3λ ---> equation 1
We need to find highest order yes so check at which values of θ the sinθ has its maximum value, that is sin90 = 1
so we get other equation :
d x sin90 = nλ ---> equation 2
Now divide Equation 1 by 2 so that d and λ gets cut and you get n
so sin45 = 0.7 and sin90 = 1 ; (d x 0.7 = 3λ) / (d = nλ) this will give :
0.7 = 3/n
so n = 3 / 0.7 ≈ 4
so you get your answer as 4th :)
 
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Student12 said:
Doubts in waves :Question 25 (B)
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s05_qp_1.pdf
Question 24 (B)http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w05_qp_1.pdf
Click to expand...
I = kA²
k=I/A² (equation 1)
at other position of meter that is equation 2 :
2I=k(x²)
2I= (I/A²) * x²
( 2I * A² ) / I = x²
Taking √ both the sides, x = √ 2 * A

24)
I α a^2 and I α f^2.

Rather than doing all the math to do this, compare the amplitude and frequency of the waves and use the formula to figure out this stuff:

If Q's amplitude is twice as much, the intensity will be four times as much.
If Q's frequency is half that of P, the intensity will be one-fourth.

Net change = 0, so the intensity remains the same.
 
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