CSSA Exam - How was it ? (1 Viewer)

[hasm]

underthesun, well, that's what I put, and I got it
Yes, I got full marks in both potential energy q's . Are you talking about the written one or the calculation specifically?

 

[underthesun]

multiple choice

boo, everytime i read these threads, the less mark it seems I am getting..

maybe i'll stop this habit

 

[wogboy]

Actually the emf produced by the photoelectric effect is independent of the intesity of the light. It just depends on the frequency of the light.

So then you might ask what happens when you increase the intensity of the incoming light (but not its frequency). Only the current increases, but the emf isn't affected. This is because even if you increase the intensity, the energy per unit charge is still the same (each electron still receives the same amount of energy), so the emf is unchanged (emf = energy/charge). It's just there will be more electrons that will be ejected, so the current will increase.

So I believe the correct answer for the multiple choice question is increasing the frequency (not intensity) causes a increased emf.

 

[Huy]

Originally posted by wogboy
Actually the emf produced by the photoelectric effect is independent of the intesity of the light. It just depends on the frequency of the light.

So then you might ask what happens when you increase the intensity of the incoming light (but not its frequency). Only the current increases, but the emf isn't affected. This is because even if you increase the intensity, the energy per unit charge is still the same (each electron still receives the same amount of energy), so the emf is unchanged (emf = energy/charge). It's just there will be more electrons that will be ejected, so the current will increase.

So I believe the correct answer for the multiple choice question is increasing the frequency (not intensity) causes a increased emf.

I'm going to have to remember this point, because our teachers are convinced that it should be increasing intensity = increased emf (i think it was A).

But I put the frequency (I think it was C?), as below a certain frequency no current was measured.

 

[underthesun]

You see, these kinds of problems happens when students gets too smart, and teachers are required to test students on things, that sometimes the teacher themselves have no concrete understanding on..

edit: whoops, i hope no BOS officials read my slander. Teachers are the best tho, they dedicate their time towards our good, and the country's education. They're truly the underrated hero of our country..

 

[The One(Vers 2)]

Originally posted by wogboy
Actually the emf produced by the photoelectric effect is independent of the intesity of the light. It just depends on the frequency of the light.

So then you might ask what happens when you increase the intensity of the incoming light (but not its frequency). Only the current increases, but the emf isn't affected. This is because even if you increase the intensity, the energy per unit charge is still the same (each electron still receives the same amount of energy), so the emf is unchanged (emf = energy/charge). It's just there will be more electrons that will be ejected, so the current will increase.

So I believe the correct answer for the multiple choice question is increasing the frequency (not intensity) causes a increased emf.

Damn! Another mark down the drain for not reading the q correctly.

 

[wogboy]

I'll mention another point just for interest: (it's not in the HSC syllabus, so don't worry if you don't fully understand it )

EMF (electromotive force) is NOT (always) the same as the output voltage. In a solar cell, increasing the light intensity can possibly increase the output voltage, but NOT the EMF. So what's the diff. between EMF & output voltage? Well the EMF IS the output voltage when the load resistance is infinite (or when the circuit is open, when zero current flows). Whenever current is drawn from the solar cell (i.e. the circuit is closed), this loaded output voltage is no longer equal to the EMF, but is a bit lower (in fact the loaded output voltage is proportional to the current, V = I*R ).

Whenever you measure the output voltage of a solar cell with a voltmeter, you are in fact measuring the EMF, since the voltmeter has a very very high resistance (~10 megaohms) so that little if any current flows (effectively an open circuit). As soon as you add a load resistor across the terminals of the solar cell (in parallel with the voltmeter), current flows, and the reading on the voltmeter is not the EMF. Since this loaded voltage reading is proportional to the current, an increase in incident light intensity will increase this loaded voltage reading. But the increased light intensity cannot cause the EMF to increase.

Huy, maybe your teacher is confused between loaded output voltage, and the EMF (unloaded output voltage)?

PS If you have any other questions, post them.

 

[ozan]

so, now that you have no doubt recieved your marks, what do the respective schools say is correct? surely they are not simply taking the provided catholic answers, because they were pure hoshposh, most of them. (particularly reading the sample written questions... oh my god).

our head of physics is saying intensity. mind you, our head of physics is about as useful as the proverbial inanimate carbon rod.

to me the the intensity response seems neither correct, nor particularly relevant if it were true.

 

[Ragerunner]

i just saw the marking guidelines for the medical physics section, our teacher photocopied it for us.

all i can say is i reckon the guy who wrote the exam did it overnight while chugging down 10 glasses of coffee because seriously, half the answers are WRONG or utterly suck.

i can't imagine what the rest of the paper guidelines will be like

 

[Dash]

Has anyone got their results back yet???

 

[Ragerunner]

only medical so far for me.

23/25

 

[Dash]

That heaps good....

I doubt ill get my result soon...

Our teacher is a lazy F**K!

 

[Ragerunner]

same. they marked the option and dumped the core somewhere. i doubt my school is gonna get their marks until september or something lol

 

[Dash]

Hahahaha!

Teachers should get the marks back asap...

I mean, its the freakin hsc n they're still making excuses ova marking delays!

EDIT: September?!?!?! WTF!!!

 

[Ragerunner]

well if they marked it like how they marked my halfyearly i'd say the earliest is late august

 

[Chand]

hmm..got 67%, came second..4 ppl got over 60% and 4 ppl failed..so im guessin that our avg is lower than my score..highest was 77/78%..

edit: I just got two more marks..now back to finishing the option..

 

[Dash]

Scabbing marks... My specialty

 

[Ragerunner]

my teachers never budge. Once its marked its very hard to scab any extra. they think they are never wrong -_-

 

[~TeLEpAtHeTiC~]

i'm still fucking waiting 4 my physics mark..all other subject marks i got as soon as i got back..but my teacher for physics is sooooo fucking slow...
his excuse.. he would PREFER to spend time with his kids.. wtf... i uderstand he need his family time etc... but fucking hell he is a teacher by profession os he should take sum account for it.... on top of that.. THIS IS THE HSC.. wtf..i want my marks back..and if i dont get em tuesday..he has hell to pay.....
anyways physics was my worst exam so i estimate 50-70%