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March 28, 2024, 10:48:55 pm

Author Topic: VCE Physics Question Thread!  (Read 603198 times)  Share 

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Conic

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Re: VCE Physics Question Thread!
« Reply #150 on: September 02, 2013, 10:17:49 pm »
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If the wave model was correct, there would be a delay before electrons were emitted, as it would require time for the electron to build up energy. There would also be electrons emitted for all frequencies of light, but the energy would take longer to build up. It also predicts that higher intensities would produce more current [This is actually true. This supports the particle model as higher intensities would be predicted to decrease the delay before emission, but instead there is more current]. These have been shown to be false through experiment. The particle model can explain all of these so it is more appropriate than the wave model. Since the wave model couldn't explain it and the particle model can, the particle model was reintroduced.
« Last Edit: September 02, 2013, 10:46:41 pm by Conic »
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saifh

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Re: VCE Physics Question Thread!
« Reply #151 on: September 02, 2013, 10:34:15 pm »
+1
If the wave model was correct, there would be a delay before electrons were emitted, as it would require time for the electron to build up energy. There would also be electrons emitted for all frequencies of light, but the energy would take longer to build up. It also predicts that higher intensities would produce more current. These have been shown to be false through experiment. The particle model can explain all of these so it is more appropriate than the wave model. Since the wave model couldn't explain it and the particle model can, the particle model was reintroduced.

explains it, thanks!

lzxnl

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Re: VCE Physics Question Thread!
« Reply #152 on: September 02, 2013, 10:38:12 pm »
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If the wave model was correct, there would be a delay before electrons were emitted, as it would require time for the electron to build up energy. There would also be electrons emitted for all frequencies of light, but the energy would take longer to build up. It also predicts that higher intensities would produce more current. These have been shown to be false through experiment. The particle model can explain all of these so it is more appropriate than the wave model. Since the wave model couldn't explain it and the particle model can, the particle model was reintroduced.

Erm...higher intensities DO produce more current. Another piece of evidence was the fact that intensities had no effect on the energies of the emitted electrons.
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Conic

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Re: VCE Physics Question Thread!
« Reply #153 on: September 02, 2013, 10:39:27 pm »
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Erm...higher intensities DO produce more current. Another piece of evidence was the fact that intensities had no effect on the energies of the emitted electrons.
True. I'll edit the post.
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saifh

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Re: VCE Physics Question Thread!
« Reply #154 on: September 03, 2013, 12:18:12 pm »
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Question

Explain the role of a reverse bias voltage and an ammeter in the photoelectric effect

Robert123

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Re: VCE Physics Question Thread!
« Reply #155 on: September 03, 2013, 07:35:33 pm »
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Question

Explain the role of a reverse bias voltage and an ammeter in the photoelectric effect
A reverse bias voltage can be used to find the stopping voltage (ie. when current=0A). In doing so, the kinetic energy of the electrons (since voltage=energy/coulomb(1.609*10^19 electrons I believe).  From this, we can determine the work function of the metal (amount of energy to liberate
electrons=hf-KE)

Why is momentum measured in Ns for some questions? I know the units all add up but I thought that you just keep it as kgms^-1
« Last Edit: September 03, 2013, 08:39:16 pm by Robert123 »

~T

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Re: VCE Physics Question Thread!
« Reply #156 on: September 09, 2013, 02:06:39 pm »
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Why is momentum measured in Ns for some questions? I know the units all add up but I thought that you just keep it as kgms^-1
I presume it's from Newton's second Law, which in its true form is (I'm not sure if you do methods so I don't know if you are familiar with differential notation - force is the rate of change of momentum with respect to time)

Presuming a constant mass, and given
we get
...which should hopefully seem familiar!

But if we leave it in its original form and presume a constant force, then we can write
Rearranging yields
Thus, momentum is in Ns
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Chazef

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Re: VCE Physics Question Thread!
« Reply #157 on: September 15, 2013, 03:04:10 pm »
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Do we need to know about the thermal motion of electrons (I think that's what it's called)? A question came up about it in the second atarnotes exam from the study guide in regards to an incandescent globe
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BasicAcid

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Re: VCE Physics Question Thread!
« Reply #158 on: September 15, 2013, 04:47:05 pm »
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Do we need to know about the thermal motion of electrons (I think that's what it's called)? A question came up about it in the second atarnotes exam from the study guide in regards to an incandescent globe

I'm pretty sure not but the guys at ATARnotes seem reliable.

Mind posting/PMing me the question? Maybe you're misinterpreting the question or something. :P

Robert123

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Re: VCE Physics Question Thread!
« Reply #159 on: September 18, 2013, 04:43:07 pm »
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Question related to the detailed study photonics?
By having more modes in fibre optics, does that give any more advantages?

joey7

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Re: VCE Physics Question Thread!
« Reply #160 on: September 23, 2013, 01:44:24 pm »
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In the examiners report of last years second exam, in relation to the last question it stated "a common misconception was that the electrons moved around the orbit in a wave pattern"
If someone explain to me how this is wrong that would be great

availn

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Re: VCE Physics Question Thread!
« Reply #161 on: September 23, 2013, 01:57:32 pm »
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In the examiners report of last years second exam, in relation to the last question it stated "a common misconception was that the electrons moved around the orbit in a wave pattern"
If someone explain to me how this is wrong that would be great

The standing waves you draw around the nucleus are not the paths the electron takes, i.e. they do not continually move towards and away from the centre of orbit. The electrons are a matter wave, so the standing waves show the possible circumferences the electrons can use to orbit, because with these circumferences, constructive interference occurs.
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SocialRhubarb

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Re: VCE Physics Question Thread!
« Reply #162 on: September 23, 2013, 02:33:05 pm »
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The electrons don't orbit in a 'wave' pattern - electrons are the wave. This is probably a bit tricky for most people to understand, since it's difficult to comprehend something being a particle and a wave at the same time.

The electron exhibits both particle-like properties and wave-like properties. They have a rest mass, like a particle, but it's easiest to explain the orbitals of electrons using a wave model for electrons. The electrons can only form orbits when the 'wavelength' of the electron fits exactly into the circumference of their orbit, and they form a 'standing wave' structure. The electron cannot take any other orbital, or else it will 'destructively interfere' with itself, and so it can only exist at certain orbits and at certain energy levels. If you do chemistry, this is what causes the shells and sub-shells.

So the electron's orbit is not a wave-pattern, but instead we find the orbits by treating the electron as a wave.
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lzxnl

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Re: VCE Physics Question Thread!
« Reply #163 on: September 23, 2013, 03:57:48 pm »
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The electrons don't orbit in a 'wave' pattern - electrons are the wave. This is probably a bit tricky for most people to understand, since it's difficult to comprehend something being a particle and a wave at the same time.

The electron exhibits both particle-like properties and wave-like properties. They have a rest mass, like a particle, but it's easiest to explain the orbitals of electrons using a wave model for electrons. The electrons can only form orbits when the 'wavelength' of the electron fits exactly into the circumference of their orbit, and they form a 'standing wave' structure. The electron cannot take any other orbital, or else it will 'destructively interfere' with itself, and so it can only exist at certain orbits and at certain energy levels. If you do chemistry, this is what causes the shells and sub-shells.

So the electron's orbit is not a wave-pattern, but instead we find the orbits by treating the electron as a wave.

At the same time...electrons in multi-electron atoms do not form orbitals solely when the wavelength of the electron fits the circumference of the orbit. There are electron-electron repulsions which cannot be neglected. This is why the Bohr model of the atom fails completely for even helium.
The VCE course isn't entirely right when they use the fitting standing waves argument to atoms in general. It is only valid for species with one electron, such as H, He+, Li 2+ etc...even Au 78+.

Just keep this in the back of your mind. VCE only requires the answer that electrons form standing waves around the nucleus, although they generally don't.
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sin0001

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Re: VCE Physics Question Thread!
« Reply #164 on: September 23, 2013, 04:27:28 pm »
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Need some help with VCAA's 2013 Sample exam (linked below):
http://www.vcaa.vic.edu.au/Documents/exams/physics/physics-specs-samp-w.pdf
-For 6b, isn't the Impulse meant to calculated using the resultant force, which is 17 N up (i.e. 17 N x 1.5s)? In Itute's solutions, the force of 22 N was used o.O
-For question 16a, shouldn't the graph of the induced EMF begin under the x-axis from 0 to 1 seconds and be drawn above the x-axis for 2 to 4 seconds? Well Itute, their solutions, have drawn it starting from above the x-axis; who's wrong?
-And finally, for question 18, why is the total resistance of the two wires 5 ohms? I thought the two wires would represent a parallel circuit so that the current splits up equally amongst them, so that the total resistance becomes 1.25 ohms (using: 1/R= (1/r + 1/r))

Thanks, would appreciate any help!
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