General Thoughts: Physics (1 Viewer)

panda15

Alligator Navigator
Joined
Feb 22, 2012
Messages
675
Gender
Male
HSC
2013
Lol. Would their be a mark for saying. "The photoelectric effect is the basis for its operation. The photoelectric effect is..."?
Btw would the diagram be 1 or 2 of the 5 marks?
I'd say the diagram would be worth 2.
 

anomalousdecay

Premium Member
Joined
Jan 26, 2013
Messages
5,769
Gender
Male
HSC
2013
So according to physics in focus... they are used to activate alarms and automatic doors. Is this correct? Just hoping I can get 1/5 considering I wrote all the lines. Didn't do a diagram though...
I actually wrote on mine that it uses any type of EMR and one example as is used in burglar alarms for the solar cell set-up.
I am may be wrong because I am not sure whether electrons can be knocked out of the depletion layer simply by infra-red. I did write about threshold frequency but then again you need a complex semiconductor that can still work for infra-red.
 

Menomaths

Exaı̸̸̸̸̸̸̸̸lted Member
Joined
Jul 9, 2013
Messages
2,373
Gender
Male
HSC
2013
I actually wrote on mine that it uses any type of EMR and one example as is used in burglar alarms for the solar cell set-up.
I am may be wrong because I am not sure whether electrons can be knocked out of the depletion layer simply by infra-red. I did write about threshold frequency but then again you need a complex semiconductor that can still work for infra-red.
That's not how they work. When there's a lack of incident ray (when the burger crosses the emitter) an alarm goes off due to the lack of the elections being emitted. (overly simplified)


My English is probably peaking because I'm tired af atm so excuse the B6 English :p
 

anomalousdecay

Premium Member
Joined
Jan 26, 2013
Messages
5,769
Gender
Male
HSC
2013
That's not how they work. When there's a lack of incident ray (when the burger crosses the emitter) an alarm goes off due to the lack of the elections being emitted. (overly simplified)


My English is probably peaking because I'm tired af atm so excuse the B6 English :p

I always thought it was the opposite. Does the human body release infra-red or does it absorb?
 

Menomaths

Exaı̸̸̸̸̸̸̸̸lted Member
Joined
Jul 9, 2013
Messages
2,373
Gender
Male
HSC
2013
I always thought it was the opposite. Does the human body release infra-red or does it absorb?
Releases, what do you mean opposite? Theres an emitter and an reciver, I'll show a diagram:

O-----------------------------------------------)
^Emitter............................................Receiver^
Everything's all good.
Now put a burger there

O---------- (]|||] -------------------------------)

Since the ray can't hit the receiver, an alarm goes off :)
 
Last edited:

anomalousdecay

Premium Member
Joined
Jan 26, 2013
Messages
5,769
Gender
Male
HSC
2013
Not the ones I have in my house.
Ours is just infra-red and when someone walks past it goes off.
 

Menomaths

Exaı̸̸̸̸̸̸̸̸lted Member
Joined
Jul 9, 2013
Messages
2,373
Gender
Male
HSC
2013
Not the ones I have in my house.
Ours is just infra-red and when someone walks past it goes off.
Obviously there can be different types of alarms that work on different principles.
 

anomalousdecay

Premium Member
Joined
Jan 26, 2013
Messages
5,769
Gender
Male
HSC
2013
I really, really, really hope that the markers for my paper have done Age of Silicon, cause they will know what point I tried to make.
 

MATHmaster

Member
Joined
Dec 3, 2011
Messages
195
Location
Sydney
Gender
Male
HSC
N/A
Unless she is in the group of teachers who come up with the marking scheme for the question, her 'confirmation' means diddly squat!

In terms of the syllabus, photocells and solar cells are two COMPLETELY different dot points, in two COMPLETELY different sections.

Whenever the word photocell or photoelectric cell has been used in HSC previously, it has been referring to the anode / cathode arrangement. A solar cell has never been referred to as a photocell previously.

I can see the arguments for either side, but i would put my money on them saying anode / cathode arrangement is a photocell. I suppose we need to wait til the marking guidelines are released!
Well she had a look at the paper months before it was released, and thus knew the marking guidelines beforehand. I called her and she said solar cells are fine to use and I won't get penalised for it
 

Menomaths

Exaı̸̸̸̸̸̸̸̸lted Member
Joined
Jul 9, 2013
Messages
2,373
Gender
Male
HSC
2013
Well she had a look at the paper months before it was released, and thus knew the marking guidelines beforehand. I called her and she said solar cells are fine to use and I won't get penalised for it
What? Is that why JR is coming #1 all the time?
 

nerdasdasd

Dont.msg.me.about.english
Joined
Jul 29, 2009
Messages
5,354
Location
A, A
Gender
Male
HSC
2012
Uni Grad
2017
Looks like you guys had to do a decent paper (y)
 

uart

Member
Joined
Dec 10, 2008
Messages
66
Gender
Male
HSC
N/A
This is what the Jacaranda textbook says about photocells, why are solar cells wrong to mention?

A photocell is a device that uses the photoelectric effect. These devices include photovoltaic, or solar cells, which convert electromagnetic energy, such as sunlight, into electrical energy. Other examples are photoconductive cells and phototubes.

pg 207

Someone explain why drawing a solar cell is wrong?
You make a really good point. I hate the use of the term photocell to describe a light dependent resistor.

The technically correct term for a solar cell is a “photovoltaic cell” and the best term for a light dependent resistor is (in my opinion) “a light dependent resistor” or a "photoresistor", not a “photocell”. (I always prefer a more descriptive name over one less so).

Also the word “cell” usually carries a connotation of a source of electrical power when used in an electrical context, which is another reason not to like the term “photocell” to describe a light dependent resistor. Having said that however, people do often use the term photocell to refer to a light dependent resistor, so I think that was indeed what you were expected to describe here. Sorry :(

The use of the term photocell to describe what many would more commonly know as a light dependent resistor, and could easily confuse with a photovoltaic cell, is a total act of bastardy by the BOS. Particularly to have a whole 5 mark question hanging on just the meaning of this one word, with absolutely no other clues or context to guide you. I mean how fricking hard would it have been for them to word the questions as:

With the aid of a diagram explain how a photocell (light dependant resistor) works.

Grrrrrrrrrr.
 
Last edited:

uart

Member
Joined
Dec 10, 2008
Messages
66
Gender
Male
HSC
N/A
I got 51.91 but not sure why g is 9.8. Is the space station being tested on earth
No, but it's simulating the gravity of Earth, hence we use the same value.

BTW. Sorry I haven't read all the replies here but from what I've read it looks like no one has put this answer into units of *rotational* speed (eg radians per second, revs per second, revs per minute etc).

The correct linear speed at the circumference is 51.91 m/s, but shouldn't you divide this by (2 pi r) and give the results in revolutions per second or similar units? Or is circumferential speed considered a good enough answer for "rotational speed".
 
Last edited:

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top