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March 29, 2024, 01:50:14 am

Author Topic: VCE Physics Question Thread!  (Read 603249 times)  Share 

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Zealous

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Re: VCE Physics Question Thread!
« Reply #735 on: November 09, 2014, 03:44:08 pm »
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How can we conclude that the path differences are the same?
You can make that conclusion because the position Y is in the exact same spot with both patterns.  The light from both slits has still travelled the exact same distance to reach point Y, so the difference in the path they take will still be the same.



If you see the diagram, there has been no change to the path of the light to reach point Y, the only thing that has changed is the spacing of the pattern because of the new wavelength of light.
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Plitzer

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Re: VCE Physics Question Thread!
« Reply #736 on: November 09, 2014, 05:04:15 pm »
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Could someone explain slip rings in reference to AC generators for me please? I'm having trouble understanding textbook definitions, thanks  :)
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Rishi97

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Re: VCE Physics Question Thread!
« Reply #737 on: November 09, 2014, 05:19:08 pm »
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Could someone explain slip rings in reference to AC generators for me please? I'm having trouble understanding textbook definitions, thanks  :)

Basically, slip rings allow the AC current induced in the loops to be transferred to the LOAD. Generators that are fitted with slip rings produce AC
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Mujteba

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Re: VCE Physics Question Thread!
« Reply #738 on: November 09, 2014, 05:43:11 pm »
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Could someone explain slip rings in reference to AC generators for me please? I'm having trouble understanding textbook definitions, thanks  :)

Also compared to the commutator, slip-rings remain stationary and do not rotate with the coil. The only place they are seen as far as the physics course is concerned is on the AC generator. One problem with slip rings though is because of the metal to metal contact between the coil and the rings they are very prone to wear and also cannot handle vibration too well as the coil can temporarily lose contact with the slip rings and cause sparks. This is why in many motor vehicles an alternator is used which rotates the magnet rather than the coil and hence eliminates the need for slip rings.

Went a bit off track but hope that covered all bases  ;D

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Re: VCE Physics Question Thread!
« Reply #739 on: November 09, 2014, 06:06:37 pm »
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Also compared to the commutator, slip-rings remain stationary and do not rotate with the coil. The only place they are seen as far as the physics course is concerned is on the AC generator. One problem with slip rings though is because of the metal to metal contact between the coil and the rings they are very prone to wear and also cannot handle vibration too well as the coil can temporarily lose contact with the slip rings and cause sparks. This is why in many motor vehicles an alternator is used which rotates the magnet rather than the coil and hence eliminates the need for slip rings.

Went a bit off track but hope that covered all bases  ;D
How is the current directed in the coil, though? Like a split-ring commutator reverses the current every 180degrees but slip rings maintain an AC current within the coil? How does this keep it rotating? Maybe I should have been more specific as this is really what I want to know. That gave me heaps of useful information though - so thank you!
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Re: VCE Physics Question Thread!
« Reply #740 on: November 09, 2014, 06:20:33 pm »
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They're just a circular electrical contact so that as the wires spin, they're always in contact with these rings which then connect the spinning wire back to the rest of the circuit.
As for the current in the coil, if you have an alternator, the current is generated by the motion of the coil through principles you're hopefully aware of by now. Its direction is determined by whether the flux is increasing or decreasing.
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Re: VCE Physics Question Thread!
« Reply #741 on: November 09, 2014, 06:36:24 pm »
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For the exam, are you not allowed to write anywhere in the border? Or is it only on the side closest to the centre?
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Re: VCE Physics Question Thread!
« Reply #742 on: November 10, 2014, 08:56:28 am »
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For the exam, are you not allowed to write anywhere in the border? Or is it only on the side closest to the centre?

You can't write outside the border. So only within the vicinity of that box. :)

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Re: VCE Physics Question Thread!
« Reply #743 on: November 10, 2014, 09:11:59 am »
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Would somebody be able to explain modulation and demodulation? Thanks  :)

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Re: VCE Physics Question Thread!
« Reply #744 on: November 10, 2014, 10:46:25 am »
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Would somebody be able to explain modulation and demodulation? Thanks  :)

You have some information you want to transmit, and it's in the form of a low-frequency wave. We'll call this the signal.

You know that a low frequency signal wont make it very far if you try to transmit it through a wire or the air, or something, so you want to encode your information onto a high frequency wave that we'll call the carrier. This might be a light wave, for example. The modulated wave wont suffer as much of a loss when transmitted over a distance, so your information goes further.

Modulation is the process of encoding the information into the carrier wave, and in VCE physics we talk about intensity/amplitude modulation which means we encode the changes in signal into changes in amplitude of the high-frequency carrier. (there's also frequency modulation where changes are mapped onto changes in frequency).

Demodulation is the reverse process, where the information is extracted from the modulated wave (after transmission), so basically you read the changes in amplitude of the incoming wave and that's your signal.
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Yacoubb

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Re: VCE Physics Question Thread!
« Reply #745 on: November 10, 2014, 10:53:44 am »
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Modulation is the process of encoding the information into the carrier wave, and in VCE physics we talk about intensity/amplitude modulation which means we encode the changes in signal into changes in amplitude of the high-frequency carrier. (there's also frequency modulation where changes are mapped onto changes in frequency).

So if we were using a light beam, would modulation be that we encode the changes in the signal into changes in the light brightness?

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Re: VCE Physics Question Thread!
« Reply #746 on: November 10, 2014, 11:40:27 am »
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Is it necessary to put a negative in front of voltage gain if the amplifier is inverting? Do you lose marks if you don't?

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Re: VCE Physics Question Thread!
« Reply #747 on: November 10, 2014, 11:44:07 am »
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So if we were using a light beam, would modulation be that we encode the changes in the signal into changes in the light brightness?

yeah, intensity (brightness) is proportional to amplitude squared, so essentially you're making it brighter/dimmer in accordance with the information signal you're trying to send.

Is it necessary to put a negative in front of voltage gain if the amplifier is inverting? Do you lose marks if you don't?

Do gain as the absolute value of the gradient (no minus sign either way), and then if necessary mention that it's an inverting amplifier when they ask. Putting the negative there is fine too, afaik.
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Re: VCE Physics Question Thread!
« Reply #748 on: November 10, 2014, 11:48:35 am »
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Also, Question 17b in VCAA exam 2013.

It says that there is zero emf when there is no change in flux (i.e gradient of the graph is 0) and list the possible times as 0.5,1,1.5. Wouldnt 0, 2 and 2.5 be included?


Nevermind I'm an idiot. It specifies a time restriction, gotta watch out for those aye.

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Re: VCE Physics Question Thread!
« Reply #749 on: November 10, 2014, 04:03:51 pm »
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How should we deal with the negative sign in Faraday's law when computing the average emf induced?

Quite clearly we have emf = -N(change in flux/change in time), which is likely to come out as a negative value - how should we 'convert' this to a positive average emf induced, in terms of mathematically sound working?
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