Exam thoughts?? (1 Viewer)

mrstripedshades

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Found it really easy tbh especially in comparison to my trials. Most trouble I had with was mc probably and kinda bullshitted some of Astro
 

DatAtarLyfe

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It definitely was one of the easiest papers in the last couple of years.
I expect the cut off will be ~85-87
 

Ambility

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I think it was a pretty easy exam. I finished with plenty of time to spare. Here's a couple questions for everyone:

What did everyone use for their three discoveries including the electric generator?
Did anyone else freak out when they saw eV and didn't know what it was?
For the solar panel multiple choice question, does light create electron hole pairs or a pd between the PN junction?
For the last multiple choice question, with a DC motor connected to an AC power supply, does it vibrate to the frequency of the AC or does it alternate a half turn backwards and forwards?
For the makeshift light source of Mars, what happens when the switch is open?

Cheers.
 

henryg124

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^ for the last MC
I thought it only turned clockwise because the AC turns the magnets into electromagnets which changes the electromagnetic field constantly, turning the coil constantly
 

cookie_dough

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1. I wrote about semiconductors and superconductors
2. Nope :)
3. I am under the impression it was electron-hole pairs
4. I thought it alternated half turn forwards then half turn backwards
5. I said that mass will fall faster when switch is open. I thought that the induced emf generates a current opposing the change in flux (Lenz's Law) and therefore slowing the rotation when the switch is closed, cos current is allowed to flow. BUT I was not sure
 

RachelGreen

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1. I wrote about semiconductors and superconductors
2. Nope :)
3. I am under the impression it was electron-hole pairs
4. I thought it alternated half turn forwards then half turn backwards
5. I said that mass will fall faster when switch is open. I thought that the induced emf generates a current opposing the change in flux (Lenz's Law) and therefore slowing the rotation when the switch is closed, cos current is allowed to flow. BUT I was not sure
I feel like it would be incorrect to talk about Lenz law for 5. I just said that due to law of conservation of energy, the rotor coils would be harder to turn (rotational kinetic energy) would decrease as the mass falls faster, thus mass falls experiences opositional force compared to when switch it open
 

RachelGreen

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For the last question in core topics, regarding Mars and energy supplies to light bulb. Did anyone get 7.48 joules??? Or am I wrong
 

thomasdo1

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^ for the last MC
I thought it only turned clockwise because the AC turns the magnets into electromagnets which changes the electromagnetic field constantly, turning the coil constantly
split-ring tho
 

Spoderman19

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That's the idea of a universal motor. The split-ring reverses the current direction (so keeps the current in the rotor coil constant in direction) but the magnetic field reverses direction due to the AC (instead of the current changing direction of a normal DC motor) to keep the torque constant in direction.
 

jazz519

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I think it was a pretty easy exam. I finished with plenty of time to spare. Here's a couple questions for everyone:

What did everyone use for their three discoveries including the electric generator?
Did anyone else freak out when they saw eV and didn't know what it was?
For the solar panel multiple choice question, does light create electron hole pairs or a pd between the PN junction?
For the last multiple choice question, with a DC motor connected to an AC power supply, does it vibrate to the frequency of the AC or does it alternate a half turn backwards and forwards?
For the makeshift light source of Mars, what happens when the switch is open?

Cheers.
When the switch is open the rotor coil in the AC generator still experiences a change in magnetic flux which induces an emf, BUT because the circuit is not closed no current can form and therefore the light bulb does not glow
 

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