# Some questions (1 Viewer)

#### GaganDeep

##### fffff
As astronaut of Mass 08 kg experiences a force 01 1176 N from his seat during launch when the rocket is just above the launch pad. What is the acceleration of the rocket.
Compare the conduction of insulators and intrinsic semiconductors at absolute zero
Compare the conduction of insulators and intrinsic semiconductors at room temp
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[FONT=&quot]Use band theory to explain to explain ur answers to above.

[/FONT][FONT=&quot]Describe how the spectral class of a star is obtainted.

what's intrinsic conduction and extrinsic relating to doping

[/FONT] 9. How many photons will be emitted from a 60 watt monochromatic light of wavelength 500nm shining for 1 minute?
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A. 1.5 x 1017
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B. 9 x 1018
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C. 1.5 x 1020
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[FONT=&quot]D. 9 x 1021[/FONT][FONT=&quot]

[/FONT]
9. Sam is sitting down watching the clock when Samantha flies past at close to the speed of light. Which of the following situations will occur according to Einstein’s theory of special relativity?
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A. Sam will see Samantha’s clock running slower than his and Samantha will see Sam’s clock running faster than hers.
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B. Sam will see Samantha’s clock running faster than his and Samantha will see Sam’s clock running slower than hers.
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C. Both Sam and Samantha will see each other’s clock as running faster than their own.
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D. Both Sam and Samantha will see each other’s clock as running slower than their own.

[FONT=&quot] <!--[if !supportLineBreakNewLine]-->
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Some astronomers have proposed the Terrestrial planet Finder array, a series a four satellites, each with an optical telescope, placed 1 km apart. With this array scientists hope top image planets around stars up to 50 light years away<o>></o>>
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Explain why adaptive optiocs is not necessary for the telescopes on board these satellites
Explain why the array uses four statllites rather than just one<o>></o>>
Describe how the resolution of the telescope would be affected by moving the satellites closer together<o>></o>>
State the name of a successful astronomical satellite and outline its contribuition to astronomy

Also what about the deflection plates in CRO and Tv. Tv uses just mag and CRo both elec and magnetic field for deflect right<o>></o>>

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#### Naylyn

##### Member
Assuming that should be 80kg
N = ma + mg
N = m(a + g)
a + g = F/m
a = F/m - g
a = 1176/80 - 9.8
a = 4.9m/s^2

#### Naylyn

##### Member
The answer to the relativity question should be D
since t1=t2/sqrt(1-v^2/c^2)
time will appear to be dilated because the speed squared will always be positive

#### commonwealth

i'm pretty sure it should be (A) for the mutiple choice...
just think of the twins paradox

#### ianc

##### physics is phun!
GaganDeep said:
[FONT=&quot]
[/FONT] 9. How many photons will be emitted from a 60 watt monochromatic light of wavelength 500nm shining for 1 minute?
<o>> </o>>
A. 1.5 x 1017
<o>> </o>>
B. 9 x 1018
<o>> </o>>
C. 1.5 x 1020
<o>> </o>>
[FONT=&quot]D. 9 x 1021[/FONT]
Ok there are 2 steps to this: first find the energy of one photon of this light and find the total energy that is emitted by the globe. Then divide.

(btw all these formulas are on the formula sheet)

So:
Energy for one photon:
E=hf
E=hc/λ
= (6.626*10-34)(3*108) / (500*10-9)
=
(6.626*10-34)(3*108)(500*109)
= something

Total energy:
Energy=VIt
(since P=VI)
Energy=Pt
= (60)(60)
=3600 J

Dividing the total energy outputted by the energy for one photon on the calculator...

And the answer i got was D: 9*10-21 photons

youve just got to make sure you use the right units - ie seconds for time, metres for wavelength

GaganDeep said:
9. Sam is sitting down watching the clock when Samantha flies past at close to the speed of light. Which of the following situations will occur according to Einstein’s theory of special relativity?
<o>> </o>>
A. Sam will see Samantha’s clock running slower than his and Samantha will see Sam’s clock running faster than hers.
<o>> </o>>
B. Sam will see Samantha’s clock running faster than his and Samantha will see Sam’s clock running slower than hers.
<o>> </o>>
C. Both Sam and Samantha will see each other’s clock as running faster than their own.
<o>> </o>>
D. Both Sam and Samantha will see each other’s clock as running slower than their own.
Like commonwealth said, think of the twin paradox. But wouldn't the answer then be D because, relative to one another, Sam and Samantha are both moving at a speed close to c and so they both think that each other's clock is slower than their own???? but i'm not sure, those relativity questions can send your brain in circles.....

Not sure about the next few questions cos i don't do the astrophysics option....

Then for the motors question:

GaganDeep said:

When the motor is running slower, there is less back emf so more current is drawn from the power supply. At higher speeds, there is more back emf induced by the motor's rotation so less current is drawn. The other 3 graphs are sloped the wrong way, so C is the only answer.

GaganDeep said:
Also what about the deflection plates in CRO and Tv. Tv uses just mag and CRo both elec and magnetic field for deflect right>>
I don't think it really matters what deflection system they use, in the excel book it says they use electrical plates but I don't think it really matters

Just if theres a question on it make sure you say something about there being 2 sets of plates/coils - one for horizontal deflection and the other for vertical.

edit: I was just looking at this syllabus, and this is the dot point relating to your question:

It says "Deflection plates or coils", so either is acceptable

Hope this helps!

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#### The Gate Keeper

##### Member
for the relativity question, both aren't travelling at the speed of light though, only Samantha is. The fact that Sam can see Samantha travel at the speed of light, well good luck on that, but i would say the answer is A as well.

Compare the conduction of insulators and intrinsic semiconductors at absolute zero
Compare the conduction of insulators and intrinsic semiconductors at room temp
Use band theory to explain to explain ur answers to above.
For insulators, the valence band is filled with electrons, no open spots are available. This is true for both room temp and absolute zero conditions. However, in semiconductors, at room temp the valence band has holes as the electrons are able to move across to the conduction band because thermal energy allows for the electrons to cross the gap. However, at subzero, there is no thermal energy, and therefore electrons cannot cross the gap, meaning semiconductors' valence bands are then filled (no holes), making them equal to that of an insulator's valence band.

Like ianc, i don't do astrophysics, so can't help you with that question, and the other questions have been answered.

#### ianc

##### physics is phun!
GaganDeep said:
[FONT=&quot]
what's intrinsic conduction and extrinsic relating to doping
[/FONT]
just saw another question hiding in that tiny font...

intrinsic conduction simply describes the conduction in a naturally occurring semiconductor (group IV element such as Si or Ge).

extrinsic conduction is the artificially boosted conductivity of a semiconductor by doping it to either make it P-type or N-type

#### Naylyn

##### Member
commonwealth said:
i'm pretty sure it should be (A) for the mutiple choice...
just think of the twins paradox
Look at it this way;
considering the observer who is moving fast the stationary observer can be considered to be moving at -v, where v is the speed of the observer, then v^2 will be positive and time will appear to have dilated, by the time dilation formula.

Also when considering the twins paradox both will think the other is moving slower and it is only through general relativity that it is known that the travelling twin will be younger, but because the syllabus doesn't do general relativity they try to explain the twins paradox through special relativity, which is really quite stupid.

#### Naylyn

##### Member
I just rang the HSC advice line and the answer to the relativity one is D

#### The Gate Keeper

##### Member
Thanks for putting explaination to it all Naylyn. It is always good to debate, and understand the correct answer, i just hope i can remember this type of stuff tomorrow.

#### Naylyn

##### Member
The Gate Keeper said:
Thanks for putting explaination to it all Naylyn. It is always good to debate, and understand the correct answer, i just hope i can remember this type of stuff tomorrow.
I agree debate is good and there is no point knowing the correct answer if you dont know why it is correct...any way good and remember the HSC isn't the end of the world

#### The Gate Keeper

##### Member
yea i know it isn't. But would be good to do as well as i could, that way, gives me the best chance of getting into the course i want at the unis i would like to go to. Otherwise, there's always TAFE. Not all that bad.

Good luck all with tomorrow's physics exam.