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Physics: Post your doubts here!

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Q30- d sin theta=n lambda
sin theta=1 as its normal to the grating. then d=1/N. N=300 per mm means 300000 per m. so 1/300000=(690*10^-9)*n
n will be around 4. then multiply by 2 and u get 9 :D

how come you multiply it by 2?
 
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you always multiply by 2 to find the maxima. i think it was because n is only for one side or something...i dont really remember the reason :p but just remember 2 do it everytime :)


and for 27..if the diameters being halved shouldnt it be 1/2?

sorry can you do 36 as well..last question :p
 
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and for 27..if the diameters being halved shouldnt it be 1/2?

sorry can you do 36 as well..last question :p
no diameter gets halved but the radius gets decreasd by 1/4th then. Try it using a value for diameter and find the area. Then repeat using half value of diameter. Area will be 1/4th :)
 
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and for 27..if the diameters being halved shouldnt it be 1/2?

sorry can you do 36 as well..last question :p
you have to split it into 2 parts. 1st take the positive part. I=2. then find P. P=I^2R=2*2*100=400W
then take the negative part where I=-1. P=-1*-1*100=100
then average it as they want the mean power. so 100+400/2=250W :)
 
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1__Two springs P and Q both obey Hooke’s law. They have spring constants 2k and k respectively.
The springs are stretched, separately, by a force that is gradually increased from zero up to a
certain maximum value, the same for each spring. The work done in stretching spring P is WP,
and the work done in stretching spring Q is WQ.
How is WP related to WQ?
A WP =  1/4 WQ B WP =1/2  WQ C WP = 2WQ D WP = 4WQ
i get C ... but the answer is B


2___A wave of amplitude a has an intensity of 3.0Wm–2.
What is the intensity of a wave of the same frequency that has an amplitude 2a
A_12 .. i used I>A^2 and still not coming
 

Tkp

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M/J/12 paper 12 questrion no 30. If anyone can help, I would be very obliged.
see the cro rises to a maximum at a position X, falls to a minimum and then rises once again to a maximum at a
position Y. so the distance between the adjacent antinodes is .5lambda
so 33*2/100=lambda
v=flambda
and f is 500
so the time base for 1 div is .5ms
so it takes 4 div to complete a wave that means 4*.5
=2 ms
2/1000=1/500
and f=1/t
so it matches and the ans is B
Hope ur clear nw
 
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