VCE Physics Question Thread!

[rui97]

For complete diffraction, you need your slit to be smaller than the wavelength.

Is complete diffraction the same as significant diffraction?

[lzxnl]

No. Complete diffraction is when your light wave completely spreads out around the slit with no intensity minimum. Significant diffraction is when the most significant part of the light wave is wide, but it does allow for intensity minima. Look at http://en.wikipedia.org/wiki/Diffraction and the pictures for this.

[Brunette15]

Are there any main difference's between a split ring commutator and slit ring commutator that we should note? So far on my cheat sheet I have only put that split rings are for DC and produce a DC output, and slip rings are for AC and produce an AC output... 

[RKTR]

Are there any main difference's between a split ring commutator and slit ring commutator that we should note? So far on my cheat sheet I have only put that split rings are for DC and produce a DC output, and slip rings are for AC and produce an AC output... 

Split ring reverse direction of current every half turn but slip ring maintains it.
Can anyone confirm?

[Thorium]

Split ring reverse direction of current every half turn but slip ring maintains it.
Can anyone confirm?

Yep that is right.

In addition, in generators, slip rings are used to produce AC EMF. This type of generator is also called alternator. And split ring is used to reverse current every half cycle, so that the produced EMF remains in the same direction. (So DC)

The Voltage vs time graph of an alternator looks like a sinusoidal graph.
If a split ring is used, the negative values of the sinusoidal graph are flipped, i.e. they become positive.

Hope that helps

[speedy]

For the cheat sheet, do we have to stick the two A4 pieces together?

[myanacondadont]

For the cheat sheet, do we have to stick the two A4 pieces together?

Afaik they have to be bound together by tape. Otherwise you can use a single piece of A3 doublesided.

[myanacondadont]

Got a few questions:

What should I chuck on my cheat sheet for modulation? I don't think we touched on it during the year but the exams seem to look to ask questions on it. I was thinking of just putting what an information signal/unmodulated signal/modulated signal/carrier wave looks like.

If anyone is doing structures & materials; What's the difference between strain energy and toughness? Are they both the same thing or is one multiplied by volume? Also, when reading a f-x graph do we calculate the area under the graph (similar to a stress-strain graph) for strain energy?

[silverpixeli]

Got a few questions:

What should I chuck on my cheat sheet for modulation? I don't think we touched on it during the year but the exams seem to look to ask questions on it. I was thinking of just putting what an information signal/unmodulated signal/modulated signal/carrier wave looks like.

If anyone is doing structures & materials; What's the difference between strain energy and toughness? Are they both the same thing or is one multiplied by volume? Also, when reading a f-x graph do we calculate the area under the graph (similar to a stress-strain graph) for strain energy?

modulation: yeah just a diagram is fine, make sure you know the few key points they look for in worded questions like

• the reason for modulating signals for transmission
• the process, from modulating to sending to demodulating and what waves are involved (signal wave, carrier wave, modulated carrier wave, etc)

strain energy: the energy of an object under load due to its strain which is given by the area under stress-strain graph, then multiplied by volume. the area in question might not be the whole graph, all the way to failure.

toughness: the maximum strain energy density of a material, a property of the material that describes how much energy a unit of volume or that material can take to failure. because of this, it's always calculated as the full area under the stress strain graph, and because it's not object-specific, it's material specific, you don't multiply by volume.

hope that helps!

[speedy]

Saw this in the 2011 Exam 2 assesors report...

Spoiler

I usually just used the first and last points that are given to estimate Planck's constant -> would you lose marks for this (let's say they weren't exactly on the line of best fit)?

Edit: Yup, not marks was confirmed later in the report.

Spoiler

I'm still kinda unsure though, because my points were on the line of best fit, but I'm sure my answer was the "accepted value"

[jumcakes]

does anybody have a suitable definition for single slit interference? I have it such that when light passes through a slit it diffracts and the waves from each side interfere with each other creating bright/dark bands but am still a bit unclear.

furthermore would the purpose of modulation be to transmit information more effectively since higher frequency waves diffract less (hence why we impose the signal wave onto the carrier wave)

[lzxnl]

does anybody have a suitable definition for single slit interference? I have it such that when light passes through a slit it diffracts and the waves from each side interfere with each other creating bright/dark bands but am still a bit unclear.

furthermore would the purpose of modulation be to transmit information more effectively since higher frequency waves diffract less (hence why we impose the signal wave onto the carrier wave)

It's not like you really need a definition for this and I haven't tried to define it myself before so I'll see what I come up with here.
Huygen's wave model of light assumes that in a light wave, every point on the edge of the light wave acts as a new site of propagation of the light wave. In other words,you can think of light as originated from every single point on a light wave. Therefore, in single slit diffraction, you can think of light as radiating from every single point in the slit. Considering light being emitted from different parts of the slit and considering their path differences allows for analysis of the single slit diffraction phenomenon.

Yes, modulation transmits information more effectively, but I would have thought simply that it would have been because the shape of the original signal is more readily maintained in a high frequency wave than in a low frequency wave. Just what I always thought last year.

[speedy]

It's not like you really need a definition for this and I haven't tried to define it myself before so I'll see what I come up with here.
Huygen's wave model of light assumes that in a light wave, every point on the edge of the light wave acts as a new site of propagation of the light wave. In other words,you can think of light as originated from every single point on a light wave. Therefore, in single slit diffraction, you can think of light as radiating from every single point in the slit. Considering light being emitted from different parts of the slit and considering their path differences allows for analysis of the single slit diffraction phenomenon.

Do we need to know about Huygen's wavelet model? It hasn't been assessed before has it?

[lzxnl]

Heck no. Hence why I said you don't need a definition of this.

[speedy]

Heck no. Hence why I said you don't need a definition of this.

Ahk, yeah I just recall my teacher mentioning it and wanted to clarify