Physics marathon (hsc) (7 Viewers)

[kiinto]

He first used the magnetic field to find the deflection of the cathode ray
F(b) = F(c)
qvB = mv^2/r
q/m = mv/B

Then he aligned the beam until it was straight by using an electric field
F(b)=F(E)
qvB = qE
v=E/B

Then he subbed the velocity back into the charge to mass ratio (q/m) to get
q/m = E/B^2r

Wut?

Neutrinos which have speeds that exceed the speed of light are discovered. Evaluate the effect this would have on the scientific community

 

[Ichiii]

Yeh my bad, Forgot to put the r next to the B
Should be q/m = v/Br

 

[freeeeee]

Can someone explain to me Einstein's thought experiments involving mirrors and trains and discuss the relationship between thought and reality?

Im a bit confused as the textbook says the train is travelling at c, although i remember in an assessment task the marker crossed it out and wrote 0.95c

TY

 

[nerdasdasd]

Can someone explain to me Einstein's thought experiments involving mirrors and trains and discuss the relationship between thought and reality?

Im a bit confused as the textbook says the train is travelling at c, although i remember in an assessment task the marker crossed it out and wrote 0.95c

TY

The speed of light is c in all frames of references.

Anyways, Einstein thought that if he was in a train traveling at the speed of light , would he see himself. There were two possible situations:
A) he would see himself
B) he wouldn't se himself.
He concluded that B was correct, otherwise it would conflict with the theory of special relativity.

 

[Danstar2]

Can someone explain to me Einstein's thought experiments involving mirrors and trains and discuss the relationship between thought and reality?

Im a bit confused as the textbook says the train is travelling at c, although i remember in an assessment task the marker crossed it out and wrote 0.95c

TY

There's a good Train thought experiment, different to the one you asked, but it is easy to understand and is simply the observations between a man on the train and a man off the train.

The man sits on a train, it is travelling at c. It travels to the right. In the train, there is: A light in the middle of the carriage, two doors one at either end of the carriage. The light turns on and the man in the carriage notices that the light reaches both doors at the SAME time.

A man watches the train. Same scenario. But! The man sees the light turn on. The light reaches the left door of the train carriage first. Then the right door after.

Think about it: The light is in the centre of the carriage. It gets turned on and 'shoots' light out in all directions. BUT, the train is moving to the right. So the left door will be travelling towards the centre light, the right door will be travelling away from the centre light. Get it?

Also, with the teacher thing, I think he would have just said .95c as 3x10^8m/s is apparently impossible as it will use infinite energy to reach sufficient speed, meaning the mass of the universe and more will need to be converted to energy to travel so quickly.

 

[someth1ng]

The Law of Conservation of Momentum states that total momentum must remain constant (i.e. P-rocket + P-exhaust = 0). As the rocket flies, it burns fuel, causing it to lose mass. This means that, as the momentum of the exhaust remains constant, the velocity of the rocket must increase (mv-rocket + mv-exhaust = 0). (If worth more marks: engage F=ma/g-force choip).

The loss of mass alone doesn't cause it to speed up (or accelerate) - the actual change of momentum causes the rocket to accelerate. The loss of mass causes the acceleration to increase logarithmically.

 

[kiinto]

Can someone explain to me Einstein's thought experiments involving mirrors and trains and discuss the relationship between thought and reality?

Im a bit confused as the textbook says the train is travelling at c, although i remember in an assessment task the marker crossed it out and wrote 0.95c

TY

Your teacher may have been hinting at relativistic mass increase, where as v->c, m-> infinity. This means that the force required to accelerate to the speed of light is (F=ma) infinite, and therefore speed of light travel is impossible. However, I'm not sure that the practical impossibility of achieving c impinges upon Einstein's ability to theoretically consider it. As far as I know he considered a train at the speed of light, and I'd stick with that unless the question suggests practicality.

 

[VJ30]

The loss of mass alone doesn't cause it to speed up (or accelerate) - the actual change of momentum causes the rocket to accelerate. The loss of mass causes the acceleration to increase logarithmically.

i thought that momentum remained constant...

 

[nerdasdasd]

i thought that momentum remained constant...

The momentum changes because, momentum = force x time. BUT force = mass x acceleration.

Edit nvm, I'm wrong.

 

[deswa1]

The speed of light is c in all frames of references.

Anyways, Einstein thought that if he was in a train traveling at the speed of light , would he see himself. There were two possible situations:
A) he would see himself
B) he wouldn't se himself.
He concluded that B was correct, otherwise it would conflict with the theory of special relativity.

No- he concluded that A was correct as otherwise it would conflict with relativity as if he couldn't see himself, then that means that he is travelling at c and he has therefore worked out that his speed in an inertial frame without referring to an outside frame of reference. After concluding that he would see himself, he then realised that space and time must become relative in order for A to work

 

[VJ30]

The momentum changes because, momentum = force x time. BUT force = mass x acceleration.

DAFUQ??? momentum= mass x velocity......

 

[nirukk]

This question came up in my trial: With an aid of a diagram or otherwise, explain how a solar cell works. (5marks)

 

[deswa1]

i thought that momentum remained constant...

Momentum does remain constant. The exhaust gases are ejected at a constant speed and rate, thus the momentum of the exhaust gases is constant. The momentum of the rocket therefore also remains constant (in the other direction). As the mass of the rocket is decreasing however but the momentum remains the same, then its velocity must be increasing-> acceleration. This is also shown through F=ma, because the thrust of the rocket (F) remains constant but m decreases, therefore a must increase

 

[kiinto]

The momentum changes because, momentum = force x time. BUT force = mass x acceleration.

That's impulse. Momentum = Mass * Velocity.

Law of Conservation of Momentum states that momentum is a closed system (i.e. total momentum remains constant).

 

[nirukk]

DAFUQ??? momentum= mass x velocity......

Impulse you mean ?

 

[VJ30]

Impulse you mean ?

i meant momentum...the original thing i wrote!

 

[deswa4]

Momentum does remain constant. The exhaust gases are ejected at a constant speed and rate, thus the momentum of the exhaust gases is constant. The momentum of the rocket therefore also remains constant (in the other direction). As the mass of the rocket is decreasing however but the momentum remains the same, then its velocity must be increasing-> acceleration. This is also shown through F=ma, because the thrust of the rocket (F) remains constant but m decreases, therefore a must increase

WHAT a HERO!

 

[kiinto]

This question came up in my trial: With an aid of a diagram or otherwise, explain how a solar cell works. (5marks)

Solar cells exploit the photoelectric effect to function. P and n-type semiconductors are placed side-by-side to form a junction. When light falls upon the n-type semiconductor, electrons are excited and move across to the p-type semiconductor. This sets up a potential difference across the junction which accelerates electrons back across the junction and blocks them from returning back over it. If connected to a circuit, this will generate a current which can power a load. (Diagram)

The Jacaranda is pretty poor on the explanation of Solar Cells, so I'm unsure, when excited do photoelectrons move around the circuit to the p-type layer to create the potential difference, or across the junction?

 

[Keelan134]

WHAT a HERO!

Whats with this sexual tension between Deswa4 and Deswa 1?

Furthermore, where are Deswa 2 and 3??

 

[RishBonjour]

Whats with this sexual tension between Deswa4 and Deswa 1?

Furthermore, where are Deswa 2 and 3??

fkn lol'ed

and whats with all the confusion over momentum?

Solar cell question has been answered I think.