HSC Physics Question Thread

[S200]

Hi guys, could someone please help me in getting a basic understanding with examples of rotational and transitional velocity - Astrophysics.

Thankyoou!

Although this is more down to earth than astrophysics, this YouTube video does explain the concept of concurrent translational and rotational velocity...
Hope it helps

[dermite]

Hi there, i need some help with this question:
While drilling into a tough material, the DC motor in an electric drill is slowed significantly. This causes its coils to overheat. Explain why this occurs with reference to physics principles (4mks)

thanks in adv!

[S200]

Hi there, i need some help with this question:
While drilling into a tough material, the DC motor in an electric drill is slowed significantly. This causes its coils to overheat. Explain why this occurs with reference to physics principles (4mks)

thanks in adv!

Hmmm.
Well the motor would be under stress, and going slower. If its slower, would that mean that the slip rings are in contact longer and the current causes the overheating?

[jamonwindeyer]

Hi there, i need some help with this question:
While drilling into a tough material, the DC motor in an electric drill is slowed significantly. This causes its coils to overheat. Explain why this occurs with reference to physics principles (4mks)

thanks in adv!

Hey! To extend on above, it is back emf. In regular operation, back emf acts against the supply current to reduce the current flowing in the coils of the motor. We design motors expecting this reduced current flow. When we force the motor to slow down, we reduce the amount of back emf, since the coil experiences a lower rate of change of magnetic flux. This increases the current in the coils beyond what was designed to be tolerable for extended periods, causing the coils to overheat!

Key principles to mention in your answer would be induction and back emf

[clovvy]

Hey, I have something that has bugged me for a while regarding the solutions for the physics topic test gravity test 2 q8 solution... I am not getting the results provided in the solution when I plug them in my calculator so I am suspiscious that there may be an error made.... Finding Ep was fine, but when finding the velocity where it became an issue....

[blasonduo]

Hey, I have something that has bugged me for a while regarding the solutions for the physics topic test gravity test 2 q8 solution... I am not getting the results provided in the solution when I plug them in my calculator so I am suspiscious that there may be an error made.... Finding Ep was fine, but when finding the velocity where it became an issue....

Hey Hey! I just did the calculations, and they worked for me, may I see your working so I can see the problem?

An important note here though is how to define potential energy, especially as if you should make the surface of the earth as 0, or the centre of the earth as 0. This tripped me up a tonne, but the primary rule of thumb that occurred to me was that if they say radius, they refer to the centre of the earth. If they say altitude, they refer to the surface Nonetheless, this question is looking out for the change in potential energy. Maybe this will help in your new calculations

[clovvy]

Hey Hey! I just did the calculations, and they worked for me, may I see your working so I can see the problem?

An important note here though is how to define potential energy, especially as if you should make the surface of the earth as 0, or the centre of the earth as 0. This tripped me up a tonne, but the primary rule of thumb that occurred to me was that if they say radius, they refer to the centre of the earth. If they say altitude, they refer to the surface Nonetheless, this question is looking out for the change in potential energy. Maybe this will help in your new calculations

Unfortunately I was unable to get around that so I gave up..

My next question is "assess the effectiveness of solid state devices compared to their termionic equivalence"... This question did not have an answer provided to me, and instinct alone tell me to list the advantages of solid states instead..  How should I answer this question (this is also from Jamon's physics topic test)..

[radnan11]

this question is doing my head in, keep on getting it wrong

[S200]

Isn't it just the right hand slap rule, so force is straight down up?

And for Magnitude, shouldn't it just be that \(F=nBiL\)?

So \(20\times 0.005 \times 0.025 \times 0.15\)? So \(\therefore \quad F=0.0375\) upwards??

The angle should only affect the flux produced right?

[Fergus6748]

Isn't it just the right hand slap rule, so force is straight down up?

And for Magnitude, shouldn't it just be that \(F=nBiL\)?

So \(20\times 0.005 \times 0.025 \times 15\)? So \(\therefore \quad F=0.0375\) upwards??

The angle should only affect the flux produced right?

That's what I got as well. Except the distance is in metres for SI units. So:
15cm = 0.15m

[iimooncabbageii]

Hi, bit confused with this question.
Why is the answer A? Wouldn't the bright spot move sideways?

[jamonwindeyer]

Hi, bit confused with this question.
Why is the answer A? Wouldn't the bright spot move sideways?

Hey there!! Not quite - We have to remember we are talking about a magnetic field not an electric field! For those we use the right hand slap rule, or a similar rule.

Magnetic field to the left of the page, charges moving out of the page. So, fingers to the left of the page, thumb pointed out of the page - This points our palm downwards. However, electrons are negative charges, so we flip our answer - The electrons will experience a force upwards towards A

[clovvy]

Hey, now that I am paying close attention to Jake's lecture slide, he mentioned that the BCS theory is wrong so I decided to google it and I still don't quite understand... can anyone explain?

[jamonwindeyer]

Hey, now that I am paying close attention to Jake's lecture slide, he mentioned that the BCS theory is wrong so I decided to google it and I still don't quite understand... can anyone explain?

You don't need to! The BCS theory is what you learn in this course - With contemporary knowledge, we know it doesn't fully explain superconductivity, but that isn't something you need to worry about. For HSC Physics, treat it as gospel

[Jane20]

Hi guys
How can I explain the Meissner effect? I read different sources and they all say different things, induced current, exclusion of magnetic field. I dont know what should I write in the exam?
Thank you !!