HSC Physics Question Thread

[smile123]

HELP
I figured out a) is 18.62m/s
 but I can't find b) and c)

[jakesilove]

HELP
I figured out a) is 18.62m/s
 but I can't find b) and c)

For b) we use



The final velocity is zero, as the rock is stationary for a moment. Thus,




Now, it takes 9.00-1.30=7.70s for the rock to go from the maximum height to the ground. Thus




However, this includes the height ABOVE the building. Subtracting this, 290.5-17.69=272.8m is our answer

[jamonwindeyer]

Hey so I was reading about EMF and magnetic flux and recapping stuff and the concepts are pretty clear but I'm having trouble understanding Faraday's law's formula

http://buphy.bu.edu/~duffy/PY106/14e.GIF

like flux is BAcostheta and I understand the way A is the area and costheta is the angle made with the normal but i dont get Faraday's formula :/

thank you

Hey! So that version of the formula isn't going to be useful in the HSC - Since you'll never have to deal with Faraday's law numerically! I'll give you another version - But I will explain this one first.

\(\Delta\left(BA\cos{\theta}\right)\) - This is the change in magnetic flux. Note that the \(\Delta\) symbol just means "difference" as always. The reason it is \(BA\) is from the formula \(\Phi=BA\) - You get magnetic flux by multiplying magnetic flux density by area - Which makes intuitive sense The \(\cos\phi\) term just takes care of the angle of the field, basically

\(N\) is the number of turns in the coil you are talking about, and then the denominator represents change in time. So in words:

The induced EMF in a solenoid is equal to the rate of change of magnetic flux in that solenoid, multiplied by the number of turns in the solenoid.

Again though, you'll never use this formula algebraically in the HSC. Not assessable - Faraday's Law in this algebraic form isn't even in the syllabus so I instead tell my students to use this simpler version just for the utility:



In words: The magnitude of an induced emf is proportional to the rate of change of magnetic flux. This captures exactly the same information as above, but just in a way less technical way that is far easier to convey in exams.

Oh woops, forgot something. Notice both your formula and my formula have negative signs - We can actually mathematically prove that this negative exists in the formula, but for us, it represents Lenz's Law

[itssona]

Hey! So that version of the formula isn't going to be useful in the HSC - Since you'll never have to deal with Faraday's law numerically! I'll give you another version - But I will explain this one first.

\(\Delta\left(BA\cos{\theta}\right)\) - This is the change in magnetic flux. Note that the \(\Delta\) symbol just means "difference" as always. The reason it is \(BA\) is from the formula \(\Phi=BA\) - You get magnetic flux by multiplying magnetic flux density by area - Which makes intuitive sense The \(\cos\phi\) term just takes care of the angle of the field, basically

\(N\) is the number of turns in the coil you are talking about, and then the denominator represents change in time. So in words:

The induced EMF in a solenoid is equal to the rate of change of magnetic flux in that solenoid, multiplied by the number of turns in the solenoid.

Again though, you'll never use this formula algebraically in the HSC. Not assessable - Faraday's Law in this algebraic form isn't even in the syllabus so I instead tell my students to use this simpler version just for the utility:



In words: The magnitude of an induced emf is proportional to the rate of change of magnetic flux. This captures exactly the same information as above, but just in a way less technical way that is far easier to convey in exams.

Oh woops, forgot something. Notice both your formula and my formula have negative signs - We can actually mathematically prove that this negative exists in the formula, but for us, it represents Lenz's Law

magnetic field density is like magnetic field strength right? so B is always magnetic density?

Phew, so glad it's not tested! Although it is so fkn interesting! Thank you for explaining it, I understand the rest of what you said so i feel so proud rn

The simplified formula you showed is awesome omfg, thank you Jamon!! Wait, in the HSC can I still use the formula in an extended mark question just to show off and get marks?

Lenz's law from what I read, apparently opposes motion of the current? So the negative is because it's going in the opposing direction?

Thank you for the amazing answers, much appreciated omg

[jamonwindeyer]

magnetic field density is like magnetic field strength right? so B is always magnetic density?

Phew, so glad it's not tested! Although it is so fkn interesting! Thank you for explaining it, I understand the rest of what you said so i feel so proud rn

The simplified formula you showed is awesome omfg, thank you Jamon!! Wait, in the HSC can I still use the formula in an extended mark question just to show off and get marks?

Lenz's law from what I read, apparently opposes motion of the current? So the negative is because it's going in the opposing direction?

Thank you for the amazing answers, much appreciated omg

Everything you propose up there is correct - B is flux density which is field strength, and yep, that's the reason the negative is there

You can use the formula in those sorts of questions! But they'd be equally impressed by your version or my version, so pick your poison

[itssona]

Everything you propose up there is correct - B is flux density which is field strength, and yep, that's the reason the negative is there

You can use the formula in those sorts of questions! But they'd be equally impressed by your version or my version, so pick your poison

Yaaaaayy!!

Ooh nice, I shall do that next year in the HSC lol

[crazycodpro]

 

[wyzard]

For a), use the formula , since there are no initial vertical speed. For part b), as there are no horizontal acceleration, you can use the formula to work it out easily.

[beau77bro]

can someone please state an exact definition of in and out of phase. i understand that constructive mean they add together to produce a greater amplitude resultant wave and destructive is the reverse. but phase gets me... is 'in phase' when the crests both line up? like is that the ONLY time its in phase? or is just when they are in a phase that makes constructive interference? then out of phase means '180 difference in phase' or like the troughs line up with crests? again is it that single situation? then what about antiphase? is that when they are completely out of phase, or is that when they are out of phase completely and have the same amplitude? and what does in a constant phase mean on its own omg?


sorry for the billion questions, but appreciate any responses to as many as u can ahhahaha

[jakesilove]

can someone please state an exact definition of in and out of phase. i understand that constructive mean they add together to produce a greater amplitude resultant wave and destructive is the reverse. but phase gets me... is 'in phase' when the crests both line up? like is that the ONLY time its in phase? or is just when they are in a phase that makes constructive interference? then out of phase means '180 difference in phase' or like the troughs line up with crests? again is it that single situation? then what about antiphase? is that when they are completely out of phase, or is that when they are out of phase completely and have the same amplitude? and what does in a constant phase mean on its own omg?


sorry for the billion questions, but appreciate any responses to as many as u can ahhahaha

Yep, you're right on the money! In phase means that the two waves are exactly identical; ie they will entirely constructively interfere. Out of phase just means that they are NOT perfectly aligned; some areas will interfere constructively, but many will interfere destructively. Anti-phase is when they are perfectly unaligned; ie a creset meets a trough and cancels it out.

[beau77bro]

Yep, you're right on the money! In phase means that the two waves are exactly identical; ie they will entirely constructively interfere. Out of phase just means that they are NOT perfectly aligned; some areas will interfere constructively, but many will interfere destructively. Anti-phase is when they are perfectly unaligned; ie a creset meets a trough and cancels it out.

Yep, you're right on the money! In phase means that the two waves are exactly identical; ie they will entirely constructively interfere. Out of phase just means that they are NOT perfectly aligned; some areas will interfere constructively, but many will interfere destructively. Anti-phase is when they are perfectly unaligned; ie a creset meets a trough and cancels it out.

ohhh ok thankyou jake, you really cleared it up. thankyouuuu

[beau77bro]

why is it important that x-rays have wavelengths of similar distance to the distance between atoms in the crystal lattice in the x-ray diffraction experiments by the braggs?

also when is the next lecture from you guys?

[beau77bro]

can someone please explain the first paragraph? do we need to know this? i dont really get the apparatus or its workings/how it works. any help appreciated, thankyou lots atarnotes forum

[jakesilove]

why is it important that x-rays have wavelengths of similar distance to the distance between atoms in the crystal lattice in the x-ray diffraction experiments by the braggs?

also when is the next lecture from you guys?

To be honest, when it comes to that dotpoint I wouldn't bother knowing WHY, just that it is an important factor. Basically, the waves need to be able to 'get between' the layers, and thus create a diffraction pattern. So, wavelengths of similar size sort of allow that.

Keep an eye out for future lecture dates; we'll be doing some mid-year Trial prep lectures

No, you don't need to know the first paragraph of information.

[beau77bro]

ok thankyou jake, much appreciated, and i cant wait