CONFIRMED mc answers! (2 Viewers)

[pdoueihi]

wwell... actually not so sure anymore.. can u tell me ur reasoning for d?

ok well we know that conductance is measured by the ability of an electron to jump to the conduction band from the valence band...
therefore, it makes sense that electrons travel through conduction bands, as electrons (or holes) in the valence band of an insulator must go to the conduction band to travel to another atom, coz if they could travel in valence bands, this contradicts the notion that insulators are non-conductive as electrons cant jump to the conduction band.

i rekon 15 is D

 

[pdoueihi]

what difference does it make if its a hole or an electron... a hole is just the opposide flow direction of the electron... its more of a conceptual thing rather than a literal thing. the hole never travels... the electron travels leaving holes it the usual path on opposite direction.

hope that makes sense

 

[poisonives]

but don't the positive holes from p-type doping reside in an 'acceptor' level just above the valence band, and electrons can easily 'jump' into this level (not the conduction band)..? correct me if im wrong

 

[Kings407]

did any one else put 5 a - this is what i got wheni put tv as the dilated time on the spaceship and to as the time on earth

Yeah i put 5a) coz on the earth clock they will register what they get as the time to be the true time hence 0.40s. the time on the spaceship is there true time but not on earth therefore it is dilated according to earth.

 

[pdoueihi]

Yeah i put 5a) coz on the earth clock they will register what they get as the time to be the true time hence 0.40s. the time on the spaceship is there true time but not on earth therefore it is dilated according to earth.

u might be right... now that i think of it the earth and spacecraft both constitute an inertial frame... but the thing is... the craft is moving away if u think practically the light must travel further each time the clock ticks to get to earth, thus takes longer. correct me if im wrong

 

[pdoueihi]

but don't the positive holes from p-type doping reside in an 'acceptor' level just above the valence band, and electrons can easily 'jump' into this level (not the conduction band)..? correct me if im wrong

ur right about that acceptor lvl, but it is "above" the valence band as u said. so its definately not in the valance band as B states either way...

thats my logical explanation... tell me if i said something wrong

 

[pdoueihi]

Yeah i put 5a) coz on the earth clock they will register what they get as the time to be the true time hence 0.40s. the time on the spaceship is there true time but not on earth therefore it is dilated according to earth.

kings what school u go to?

 

[Kings407]

kings what school u go to?

Orange High School its in the central west

 

[Kings407]

u might be right... now that i think of it the earth and spacecraft both constitute an inertial frame... but the thing is... the craft is moving away if u think practically the light must travel further each time the clock ticks to get to earth, thus takes longer. correct me if im wrong

extremely good point but wont length contraction come into it coz the wave will travel at c?? im not sure i could be a completely different tangent.... hmmmmm

 

[poisonives]

ur right about that acceptor lvl, but it is "above" the valence band as u said. so its definately not in the valance band as B states either way...

thats my logical explanation... tell me if i said something wrong

well, from the definition of any semiconductor, the valence band is nearly full.
so once an electron moves into the acceptor level, these is ONE positive hole, and the rest are electrons. therefore the positiveholes move in one direction, while the electrons (successively) move in the other.
i'm fair sure of this

 

[pdoueihi]

extremely good point but wont length contraction come into it coz the wave will travel at c?? im not sure i could be a completely different tangent.... hmmmmm

lol i think were both going off on a tangent...
but if were not, then the speed of light is constant irrespective of the speed of the observer or source, so length contraction doesnt really matter for the speed of an electromagnetic wave, or distance..

 

[pdoueihi]

well, from the definition of any semiconductor, the valence band is nearly full.
so once an electron moves into the acceptor level, these is ONE positive hole, and the rest are electrons. therefore the positiveholes move in one direction, while the electrons (successively) move in the other.
i'm fair sure of this

well i duno... models have their limitations, can be interpreted differently... maybe thell take that qn out of marking, i duno i rekon both interpretations may be correct

 

[Kings407]

lol i think were both going off on a tangent...
but if were not, then the speed of light is constant irrespective of the speed of the observer or source, so length contraction doesnt really matter for the speed of an electromagnetic wave, or distance..

i reckon ur rite... probably just thinking too much and making the question harder than it should be meh nothing can be done about it now

 

[pdoueihi]

i reckon ur rite... probably just thinking too much and making the question harder than it should be meh nothing can be done about it now

maybe i am... but my teacher ses its neither of those, he says 0.5. maybe hes way off? lol maybe were both wrong i duno

 

[nty]

Re: Q5 MC - spaceship

I spent about 5 minutes on this one question... I think it was the hardest one for me.. Here was my thought process:

1) The clock on the ship should tick once per second, like all clocks do, so given the once every 0.5 seconds i assumed it was as observed from the earth, so each pulse of 0.5 seconds apart - A. (this is wrong - did not realise that clocks can tick faster =P)

2) according to substituting values in: the time dilation formula i got 0.4s - B
(but i mixed up t[zero] and t[v] so it's wrong)

3) according to logic: the pulse observed from earth the should be longer than in the spaceship. so it could be C or D

So. anyone want to explain what is the correct reasoning for C? do you just substitute the t v and c in? I think got it he right way this time and it still doesn't work..

 

[pdoueihi]

Re: Q5 MC - spaceship

I spent about 5 minutes on this one question... I think it was the hardest one for me.. Here was my thought process:

1) The clock on the ship should tick once per second, like all clocks do, so given the once every 0.5 seconds i assumed it was as observed from the earth, so each pulse of 0.5 seconds apart - A. (this is wrong - did not realise that clocks can tick faster =P)

2) according to substituting values in: the time dilation formula i got 0.4s - B
(but i mixed up t[zero] and t[v] so it's wrong)

3) according to logic: the pulse observed from earth the should be longer than in the spaceship. so it could be C or D

So. anyone want to explain what is the correct reasoning for C? do you just substitute the t v and c in? I think got it he right way this time and it still doesn't work..

lol well by common sense it has to be longer...

To get C u sub in the other way round, ie t0 for spacecraft and t for earth. u know it will take longer so u sub em in that way, not the other way...
carrect me if im wrong but i thought it was c

 

[nty]

lol well by common sense it has to be longer...

To get C u sub in the other way round, ie t0 for spacecraft and t for earth. u know it will take longer so u sub em in that way, not the other way...
carrect me if im wrong but i thought it was c

haha i forgot to root this time.

get it now. thanks!

 

[glockenspiel]

5 is not A. I don't know where your teacher got C, maybe they know something I don't... but the as the spaceship is travelling at relativistic speeds, 1 year will be longer for an observer on earth, 1.35 years. That means 1 second is 1.35 seconds, so the two pulses that occur in this 1 second will be measured as taking 1.35 seconds, hence it is .625 seconds between pulses.

I got B for 15, because an electron will move into a hole in the valence band. Then the electron behind it will fill the holl in the valence band it left, etc... so all the movement is happening in the valence band.

 

[pdoueihi]

5 is not A. I don't know where your teacher got C, maybe they know something I don't... but the as the spaceship is travelling at relativistic speeds, 1 year will be longer for an observer on earth, 1.35 years. That means 1 second is 1.35 seconds, so the two pulses that occur in this 1 second will be measured as taking 1.35 seconds, hence it is .625 seconds between pulses.

I got B for 15, because an electron will move into a hole in the valence band. Then the electron behind it will fill the holl in the valence band it left, etc... so all the movement is happening in the valence band.

lol dont worry i put c for 5 aswell. ill take off A for u but my teacher ses B... i still rekon C

 

[pdoueihi]

but the onli argument possible for those who say its A is that both of the frames are inertial, thus the time for the astronaut is diallated for the bloke on earth but for the astronaut, the bloke on earth's time is diallated in his opinion.

i still rekon C but thats a window for those who debate A...