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Physics: Post your doubts here!

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Thing is, the ray is being absorbed twice and is being total internally reflected once.
So first I is being absorbed so we have 0.39I being transmitted to the bone and muscle boundary. 0.33 times 0.39 is then being internally reflected so we have 0.33 x 0.39I. Then again when it is moving from the boundary to the outside, it is again being absrbed so we have 0.39 x 0.33x 0.39 I which is why they squared the 0.39.

Why 0.33 x 0.39I ?
 
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First, it's essential that you know the meaning and definition of internal energy.
Internal Energy: Internal Energy of a substance is equal to the sum of the kinetic and potential energies of all of it's particles.
Q2 (a) - When you freeze water, there is obviously no change in it's height and kinetic energy decreases because molecules are being cooled, so there is no increase in internal energy of the body, in fact there is a decrease. Answer is no.
For the second part, there are changes but you need to know that kinetic energy increases exponentially and potential energy decreases linearly. They have told us that the stone is falling under gravity in a VACUUM, so the answer is no.
For the second last part, there would be an increase in internal energy, because of the increase in kinetic energy, the heating process is still on constant temperature.
The answer is yes.
For the last part, even a vision less person can answer this question, i think you should try this yourself. :)
 
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Why 0.33 x 0.39I ?
Because it is after the first absroption that the internal reflection occurs. That is I is incident on the muscle and then atenuation or absroption occurs and then it reaches the boundary where it is internally reflected when it is comming back it is atenuated again.
 
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Describe the change to K.e, P.e and total internal energy of the molecules of a block of ice as it melts at 0 degree celcius ?
anyone?
 
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First, it's essential that you know the meaning and definition of internal energy.
Internal Energy: Internal Energy of a substance is equal to the sum of the kinetic and potential energies of all of it's particles.
Q2 (a) - When you freeze water, there is obviously no change in it's height and kinetic energy decreases because molecules are being cooled, so there is no increase in internal energy of the body, in fact there is a decrease. Answer is no.
For the second part, there are changes but you need to know that kinetic energy increases exponentially and potential energy decreases linearly. They have told us that the stone is falling under gravity in a VACUUM, so the answer is no.
For the second last part, there would be an increase in internal energy, because of the increase in kinetic energy, the heating process is still on constant temperature.
The answer is yes.
For the last part, even a vision less person can answer this question, i think you should try this yourself. :)
yes but the change in internal energy of a system= work done on/by a gas + change in thermal energy of the system
in the freezing part the temprature is constant but there is work done on the gas by the atmosphere cause it contracts. or is the oposite cause of abnormal behaviour of water?
 
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2,703
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273
First, it's essential that you know the meaning and definition of internal energy.
Internal Energy: Internal Energy of a substance is equal to the sum of the kinetic and potential energies of all of it's particles.
Q2 (a) - When you freeze water, there is obviously no change in it's height and kinetic energy decreases because molecules are being cooled, so there is no increase in internal energy of the body, in fact there is a decrease. Answer is no.
For the second part, there are changes but you need to know that kinetic energy increases exponentially and potential energy decreases linearly. They have told us that the stone is falling under gravity in a VACUUM, so the answer is no.
For the second last part, there would be an increase in internal energy, because of the increase in kinetic energy, the heating process is still on constant temperature.
The answer is yes.
For the last part, even a vision less person can answer this question, i think you should try this yourself. :)
http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_s13_qp_42.pdf Q2a(i) second part how did he find out the mass :S
 
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yes but the change in internal energy of a system= work done on/by a gas + change in thermal energy of the system
in the freezing part the temprature is constant but there is work done on the gas by the atmosphere cause it contracts. or is the oposite cause of abnormal behaviour of water?
Your doubt is valid, but you have made me confused as well. I'll have to check with someone else on this one. Nice thought.
 
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In communication systems,which of the uplink or downlink will swamp which because in the book says the opposite
 
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(iii) is really weird i get 746.
They already mentioned the volume of gas but they found it again. Dont get them. :p

We have to calculate the volume again, because there is a change in pressure when we put the balloons in the cylinder. So we use Boyle's law as the temperature remains constant.
Now this new volume is volume of the cylinder. It's the total of the balloons and the hydrogen volume in the cylinder. Read the question again try to visualize this, you will definitely get it! ;)
 
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Since the frequency of carrier wave is 50khz, that means the time period will be 20micro seconds. That means the small wave will be of 20micro seconds. Bandwith is 2 times the frequency of the information signal. So half of bandwith is 5khz which represents a time period of 200micro-herts. THAt meansin 200 microseconds, the amplitude changes from the highest to the next highest or vice versa. Im sure ive given you enough data to make the graph
 
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