HSC Physics Marathon 2013-2015 Archive (1 Viewer)

[el_manu]

re: HSC Physics Marathon Archive

Why is the answer C?
Is it because this a p-n junction?
Don't holes move in opposite direction to electrons?

Somone help please!

 

[el_manu]

re: HSC Physics Marathon Archive

BUMP!!!

 

[el_manu]

re: HSC Physics Marathon Archive

Why is the answer C?
Is it because this a p-n junction?
Don't holes move in opposite direction to electrons?

Somone help please!

this doesn't make sense. Please help

 

[godofindolence]

re: HSC Physics Marathon Archive

Why is the answer C?
Is it because this a p-n junction?
Don't holes move in opposite direction to electrons?

Somone help please!

This is my assumption.
To be carrying a current, it necessitates that electrons flow in opposite directions to the holes. From the right hand palm rule, the flow of holes- conventional current- would be downwards when subjected to the magnetic field. Similarly the electrons will also encounter a downward force (use your left hand) and thus, both would move to the same side of the rod (downwards).

 

[keepLooking]

re: HSC Physics Marathon Archive

"Both the positive holes flowing in one direction and the electrons flowing in the other direction will experience a force to the same side of the rod, i.e. the bottom side." - Success One.

 

[Zlatman]

re: HSC Physics Marathon Archive

Why is the answer C?
Is it because this a p-n junction?
Don't holes move in opposite direction to electrons?

Somone help please!

Use the right-hand palm rule for the holes, and left-hand (or reverse right-hand) palm rule for the electrons.

With the RHPR, point your thumb in the direction of the holes (conventional current) and fingers in the direction of the magnetic field. Your palm will be facing down, so the holes experience a force downwards.

With the LHPR, point your left thumb in the opposite direction to the holes (i.e. in the direction of the electrons) and fingers in the direction of the magnetic field. Again, your palm will be facing down, so the electrons experience a force downwards.

Thus, both the holes and the electrons move to the bottom of the rod.

(lol rekt, got beaten to it twice)

 

[el_manu]

re: HSC Physics Marathon Archive

It's a dumb question as "side" could literally mean anything.
The electrons are traveling towards us to the nearest side and holes to the far side. Yet, side the question is talking about is the up or down side. Fuckin dumb question.

 

[el_manu]

re: HSC Physics Marathon Archive

thx guys.

 

[Mr_Kap]

re: HSC Physics Marathon Archive

this is bullshit and wrong. Using the reverse right hand rule the palm faces upwards, meaning electrons deflect up

 

[atargainz]

re: HSC Physics Marathon Archive

this is bullshit and wrong. Using the reverse right hand rule the palm faces upwards, meaning electrons deflect up

This is what I was thinking, already switching to the left hand but in order to get it facing downwards, you would still need to reverse the current (direction of your thumb). I thought changing hands already did this? I could be missing something though

 

[Mr_Kap]

re: HSC Physics Marathon Archive

This is what I was thinking, already switching to the left hand but in order to get it facing downwards, you would still need to reverse the current (direction of your thumb). I thought changing hands already did this? I could be missing something though

yeh. If you use the left hand rule then you dont need to change current direction with your thumb. I think this is a faulty answer and the answer should be they move to opposite side

 

[godofindolence]

re: HSC Physics Marathon Archive

Uh, I think it's because electrons and holes travel in opposite directions the first place.

 

[godofindolence]

re: HSC Physics Marathon Archive

The acceleration of the planet is greater than the deceleration of the planet when leaving. The answer is :
According to the planet there is no change in velocity while in the frame of reference of the sun the spaceship gained speed.
If youre on a planet and you see a spaceship use the slingshot effect there would be no change in speed from your perspective

I don't understand, why is there no change in speed from the perspective of the observer on the planet?

 

[keepLooking]

re: HSC Physics Marathon Archive

I don't understand, why is there no change in speed from the perspective of the observer on the planet?

Principle of Conservation of Momentum. When the spaceship gains momentum, the planet will lose momentum hence there is no change of speed from the perspective of the observer on the planet.

 

[spatula232]

re: HSC Physics Marathon Archive

What's the purpose of the dry ice in a Wilson Cloud Chamber?

 

[mrpotatoed]

re: HSC Physics Marathon Archive

Principle of Conservation of Momentum. When the spaceship gains momentum, the planet will lose momentum hence there is no change of speed from the perspective of the observer on the planet.

The velocity change of the planet is negligible though, the velocity change of the spaceship is large

 

[Crisium]

re: HSC Physics Marathon Archive

What's the purpose of the dry ice in a Wilson Cloud Chamber?

I don't do this option but is it something to do with the dry ice melting to the carbon dioxide gas form and radiation ionising these particles and then there's something about droplets forming a path (beta has a zig zag one iirc) --> tbh I have no idea LOL I came across it a few times in chem though

 

[Mr_Kap]

re: HSC Physics Marathon Archive

The velocity change of the planet is negligible though, the velocity change of the spaceship is large

m1v1 = m2v2

The large mass of the planet, compared to the small mass of the spaceship balance out and momntum is conserved

 

[mrpotatoed]

re: HSC Physics Marathon Archive

Momentum is the same but the relative velocity would different after the slingshot effect has occurred?

 

[TQuadded]

re: HSC Physics Marathon Archive

Momentum is the same but the relative velocity would different after the slingshot effect has occurred?

Yes.

For example, if a planet is rotating at 100,000,000,000 km/h, then a spaceship takes advantage using Slingshot Effect and gains 1,000 km/h, that is a large increase of velocity for the spaceship, but barely any decrease for the planet.