HSC Physics Question Thread

[jamonwindeyer]

Hey! Thanks for response.
I don't know, I just find it confusing because if I picture myself manually rotating a motor faster, it just seems like the torque would increase.
How do I wrap my head around this? Just remember the torque equation?

Picture how fast a car is moving versus the 'revs' of the car. You can have low revs but high speed - Or, high revs but low speed. It shows that torque and speed aren't necessarily going to go up and down together - It depends on the load attached to the motor you don't need to worry about this much at HSC level!

[julies]

Hey there!

I just have a few questions from the Quanta to Quarks option module and was hoping to get some help

1. What was it about Thomson’s model that led Rutherford to believe no large angle deflections would occur?

Hey, so Thomson's plum pudding model consisted of negatively charged particles dispersed in a diffuse positively charged "dough". This dough is uniformly charged, and large in size, meaning that the charge at any particular point of the "dough" is quite weak. This is in opposition to Rutherford's model, where the small size of the nucleus essentially lends itself to carrying a very concentrated positive charge. If positive alpha particles are fired at a weakly positive region, then the deflection is expected to be small.   
Hope this helped haha

[Sukakadonkadonk]

No worries

I think keeping in mind the formula is a good thing to do. Perhaps you're trying to link increasing the rate of rotation with the concept of magnetic flux. Because indeed, when you start to turn the coil faster, the rate of change in magnetic flux increases, and the more it increases, the greater the current that is induced. But other than that, torque is only dependent on the variables I listed above because torque is the turning effect of a force acting on an object. The speed will not change how the coil will turn in terms of the forces experienced

Let me know if you have anymore questions

Alright, I think I get it. Just gotta remember formula.
Cheers!

[katnisschung]

impact of the development of the oscilloscope on experimental physics?
I talked quite vaguely in my answer....ability to make variations in electric currents visible and measure, analyse...
any specific examples?

[clarence.harre]

This the Quanta to Quarks option topic from 2010 (question 36.G)
The marking guidelines don't really give an understanding of the depth I needed to go to, so I'm hoping one of you could please check my answer.
***
Question:
'Important fundamental discoveries in physics often lead to applications which
have a significant effect on society.’

Evaluate this statement, with reference to the contributions of Rutherford,
Einstein and Fermi to the development of the atomic bomb.
***
Response:

Rutherford's analysis of 1909 Geiger-Marsden gold foil experiment catalysed the development of the Rutherford-Bohr model of the atom. It depicted the atom as consisting mainly of empty space, which separates orbiting electrons from a very small, dense, positively charged central mass (nucleus). His work pioneered the exploration of nuclear physics, and was thus significant in developing the bomb.

Einstein's 1905 'Theory of Special Relativity' proposed that a large amount of energy could be released from a small quantity of matter, commonly expressed in the equation E = mc2
where the energy of matter in its rest state is equal to the its mass multiplied by the speed of light squared. While this work was integral to the bomb's operations, his greatest contribution to its development was signing a letter in 1939 to President Roosevelt warning of German's advancements towards their own nuclear bomb.

Fermi's 1942 Chicago experiment utilised the work of Rutherford and Einstein to create the first controlled nuclear chain reaction. His nuclear pile consisted of a graphite moderator, cadmium control rods and fissile Uranium-235 pellets. After firing a neutron into the reaction chamber, he used the control rods to absorb neutrons, and thus controlled the reaction. This demonstration was integral in developing the uncontrolled chain reaction used in the bomb.

n+ 235U  >> 236U >> 139Ba + 94Kr + 3n

The bomb negatively impacted society, as it was used to systematically wipe out entire cities (Hiroshima and Nagasaki). These areas are still radioactive, and the descendants of the survivors suffer from radiation poisoning. A positive impact of the bomb was a peace based on Mutually Assured Destruction.

The statement is valid, as the exploration of nuclear physics authorised important fundamental discoveries which resulted in the development of the atomic bomb: an application of nuclear physics that had a major impact on society.

[yattmoani]

Hi guys, just got a few quick questions here. Would be great to have some help

[blasonduo]

Hi, guys, just got a few quick questions here. Would be great to have some help

Hello! Let's see what I can do!

1) For this one, we can use the simple motor effect, palm downwards, fingers into the page, leaving current going towards the LEFT. HOWEVER!!!!! This current is being induced! So it must resist the change in flux (due to the law of conservation of energy) So, current travels to the RIGHT (to R). Now, electrons will always flow in the OPPOSITE direction to the flow of current, and therefore electrons will flow to P, and thus there will be a higher concentration at P. So the answer is A.


2) The question states that the INDEPENDENT (the one we change) variable is on the x-axis. In this experiment, they changed the HEIGHT, so this eliminates both C and D instantly. The next step is to identify which graph has correctly used a "line of best fit". The two graph's points are clearly beginning to plateau, but graph B is clearly ignoring this, so it must be A.

Also, we know that doubling the height of an object dropped does not double the time falling, so it can't be linear

[yattmoani]

Hey! I had the same reasoning as you but according to BOSTES, the correct answer is actually P, hence my confusion. Not sure if its an error in the question or theres something we're both missing.

EDIT: Just saw blasonduo's reply. Thanks for the help! Really cleared things up for me

[bsdfjnlkasn]

Hello! Let's see what I can do!

1) For this one, we can use the simple motor effect, palm downwards, fingers into the page, leaving current going towards the LEFT. HOWEVER!!!!! This current is being induced! So it must resist the change in flux (due to the law of conservation of energy) So, current travels to the RIGHT (to R). Now, electrons will always flow in the OPPOSITE direction to the flow of current, and therefore electrons will flow to P, and thus there will be a higher concentration at P. So the answer is A.


2) The question states that the INDEPENDENT (the one we change) variable is on the x-axis. In this experiment, they changed the HEIGHT, so this eliminates both C and D instantly. The next step is to identify which graph has correctly used a "line of best fit". The two graph's points are clearly beginning to plateau, but graph B is clearly ignoring this, so it must be A.

Also, we know that doubling the height of an object dropped does not double the time falling, so it can't be linear

Hey

With your answer to the first question, why are we considering an induced current? Isn't the constant velocity going to ensure a constant rate of change of magnetic flux?

[blasonduo]

Hey

With your answer to the first question, why are we considering an induced current? Isn't the constant velocity going to ensure a constant rate of change of magnetic flux?

Hey! This is a REALLY great question!

This is now linking to ideas to implementation, as for this question you need to understand how electrons experience forces in a magnetic field.

The formula for the FORCE on a charged particle is:

F = qvB.

Even if the velocity and magnetic field are constant, it just means that the force the electron experiences is also constant!
So, the electrons do move!

I hope this helps! If there are any more questions about this, (I know! This part is very tricky!) I'll be happy to help

[jamonwindeyer]

Hey

With your answer to the first question, why are we considering an induced current? Isn't the constant velocity going to ensure a constant rate of change of magnetic flux?

And just to respond further, if induced EMF is proportional to the rate of change of magnetic flux, then a "constant rate of change of magnetic flux" means a constant induced EMF, which is exactly what we get here

So like, you and blasonduo are definitely saying the same thing. Your statement is totally correct - You might have just misinterpreted in your head

[justwannawish]

Hey I just have a few questions
1. Does centrifugal motion cause work to be done?
2. Does the atmosphere have mass? I know it's not exactly physics but just a curiosity

[jamonwindeyer]

Hey I just have a few questions
1. Does centrifugal motion cause work to be done?
2. Does the atmosphere have mass? I know it's not exactly physics but just a curiosity

1. Centripetal (circular) motion requires acceleration, so yes, work is done!

2. Yep, ozone particles have mass!

[justwannawish]

So when we calculate the mass of the earth to be 6.0 x 10^24 does it include the mass of the atmosphere? Or is it too small to be included?

[jamonwindeyer]

So when we calculate the mass of the earth to be 6.0 x 10^24 does it include the mass of the atmosphere? Or is it too small to be included?

Seems the mass of the atmosphere is about \(5\times10^{18}\text{kg}\), give or take, so that would be inconsequential compared to the mass of the earth - Kind of like taking your earphones out before getting on the scales maybe