Edexcel Unit 2: Physics at Work ~9th June 2014

Original post by Lewisallows

Has anybody got a solid definition for amplitude I can learn?

The maximum displacement from equilibrium position

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Reply 181

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Hey! Could someone help me with part b please. Thanks!

Reply 182

jtbteddy

Original post by yasminh118

Hey! Could someone help me with part b please. Thanks!

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Reply 183

Original post by jtbteddy

Oh thanks! That makes sense! I wonder if you could help me with this one too, I don't understand why the answer is B and why it can't be C :s-smilie:

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Reply 184

Lunarr

Original post by yasminh118

Oh thanks! That makes sense! I wonder if you could help me with this one too, I don't understand why the answer is B and why it can't be C :s-smilie:

Hey, could you explain why the point of rest on the above question is the crest of the wave?!

And with your question I'd say it's due to the fact that reflection is not linked to the angle of contact - all waves will have at least a small amount of energy reflected back whenever they reach a boundary. That would be my answer anyway, can't say for sure if it's correct.

Reply 185

jtbteddy

Original post by yasminh118

Oh thanks! That makes sense! I wonder if you could help me with this one too, I don't understand why the answer is B and why it can't be C :s-smilie:

Im not sure but I think that at angles less than the critical angle, both reflection and refraction occur.

Someone confirm this?

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Reply 186

Original post by Lunarr

Hey, could you explain why the point of rest on the above question is the crest of the wave?!

And with your question I'd say it's due to the fact that reflection is not linked to the angle of contact - all waves will have at least a small amount of energy reflected back whenever they reach a boundary. That would be my answer anyway, can't say for sure if it's correct.

Sorry I have no idea why the point of rest is at the crest :s-smilie:

So you're saying that waves will always be reflected slightly when they reach a boundary?

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Reply 187

Original post by jtbteddy

Im not sure but I think that at angles less than the critical angle, both reflection and refraction occur.

Someone confirm this?

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I think you're right! I never knew that but I found this online.

For any angle of incidence less than the critical angle, part of the incident light will be transmitted and part will be reflected. The normal incidence reflection coefficient can be calculated from the indices of refraction. For non-normal incidence, the transmission and reflection coefficients can be calculated from the Fresnel equations.

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/totint.html

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(edited 9 years ago)

Reply 188

BP_Tranquility

OP

Original post by yasminh118

Oh thanks! That makes sense! I wonder if you could help me with this one too, I don't understand why the answer is B and why it can't be C :s-smilie:

Original post by Lunarr

Hey, could you explain why the point of rest on the above question is the crest of the wave?!

And with your question I'd say it's due to the fact that reflection is not linked to the angle of contact - all waves will have at least a small amount of energy reflected back whenever they reach a boundary. That would be my answer anyway, can't say for sure if it's correct.

Original post by jtbteddy

Im not sure but I think that at angles less than the critical angle, both reflection and refraction occur.

Someone confirm this?

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Original post by yasminh118

Sorry I have no idea why the point of rest is at the crest :s-smilie:

So you're saying that waves will always be reflected slightly when they reach a boundary?

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Original post by yasminh118

I thought if the angle is less than the critical angle then light is just refracted. I'm not sure though.

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I asked my physics teacher this the other day and when the angle of incidence is smaller than the critical angle, most of the light is transmitted but some also gets reflected. However, he said that that there was no explanation for this which scientists agreed upon even at a quantum level...That seems like a really cruel question to put in

Reply 189

Catb97

1

With Electricity questions, when they ask you to explain, how do you know if they want you to explain using a description of the electrons vibrating faster etc or through use of equations?

Reply 190

Original post by BP_Tranquility

I asked my physics teacher this the other day and when the angle of incidence is smaller than the critical angle, most of the light is transmitted but some also gets reflected. However, he said that that there was no explanation for this which scientists agreed upon even at a quantum level...That seems like a really cruel question to put in

Ohh that makes sense, I was never told that before!

Reply 191

Original post by Catb97

With Electricity questions, when they ask you to explain, how do you know if they want you to explain using a description of the electrons vibrating faster etc or through use of equations?

any examples?

Reply 192

Catb97

1

Original post by yasminh118

any examples?

June 2013

Q13b
The student applies a force to the wire and measures the new length. He calculates the increase in the resistance to be 0.035 Ω. He measures the increase in resistance
and finds it to be 0.070 Ω.
The student suggests that the difference between these two values is because the
cross-sectional area of the wire changes under strain.
Explain why a change in cross-sectional area would cause this difference.

How would I know whether they want me to explain the equation R=pl/A or the actually ion lattice description?

Reply 193

Catb97

1

Can someone describe an experiment to measure the resistivity of a piece of wire?
And then how you would use the equation R=pl/A to apply to the graph you would draw?

Reply 194

PhRose

2

Explain why, when using an Ohmmeter, the resistance of the resistor should not be measured when it is in a circuit.

Reply 195

BP_Tranquility

OP