Yacoubb's Physics 3/4 Thread

[Yacoubb]

IMHO, I really think you should revise Unit 2 motion. Test your knowledge with some Year 11 motion exams. Chapter 1 in the Heinemann Physics 12 book does go over Unit 2 motion topics but not to a great depth. You might not feel like it, going back a year and all, but it's better to have that foundation first.

Option 2: If you don't believe me, try any Physics Unit 2 practice exam. PM me if you don't have any; I have quite a few. Let your performance on that be an indicator of what you need to revise from now on. Once again, there's no point in moving on when you don't understand the basics.

Thanks for that. I'm going to do that; I'll go over unit 2, and then retackle chapters 1 and 2 of the Jacaranda textbook. Thanks so much!

[Rod]

Ok I feel like I'm screwed for Physics. What do I do D: I feel like I know nothing & that's really concerning me! I've done up to chap 3 and I'm really not satisfied with my knowledge of motion. Fml! I need help! What should I do??

You have not had a single lesson of Physics, why do you feel screwed? Go over your basics in unit 2, watch some tutorials. If you need any help, PM me I've gone through it and have good notes.

PS - What happened to that chem sess LOL 

[Yacoubb]

Would this be a suitable written type answer for a question about crumple zones and how they minimise injury? Thanks

• X acts as a crumple zone, increasing the collision time between X and the occupants of Y.
• Force is inversely proportional to time; that is, as time increases, force decreases.p
• Thus, increasing collision time between X and occupants decreases the force exerted on occupants by X, in turn minimising the chance of injury.

[Rod]

Would this be a suitable written type answer for a question about crumple zones and how they minimise injury? Thanks

• X acts as a crumple zone, increasing the collision time between X and the occupants of Y.
• Force is inversely proportional to time; that is, as time increases, force decreases.p
• Thus, increasing collision time between X and occupants decreases the force exerted on occupants by X, in turn minimising the chance of injury.

That's literally exactly how I wrote it in my SAC and my teacher gave me full marks

[Yacoubb]

That's literally exactly how I wrote it in my SAC and my teacher gave me full marks

Sweet! Thanks Rod

Also, for questions asking for explanations in terms of Newton's Laws, my template would be:
* State which law the problem is relevant to & actually state the law.
* Explain the scenario
* Make explicit link to the law in which the scenario is relevant to

^^ Would this be sufficient for a 3-mark question? I'm really just compiling these because I'm going to dedicate like a whole page of my A3 cheat sheet to these template answers. VCAA seems to really like them in differentiating students.

[Rod]

Sweet! Thanks Rod

Also, for questions asking for explanations in terms of Newton's Laws, my template would be:
* State which law the problem is relevant to & actually state the law.
* Explain the scenario
* Make explicit link to the law in which the scenario is relevant to

^^ Would this be sufficient for a 3-mark question? I'm really just compiling these because I'm going to dedicate like a whole page of my A3 cheat sheet to these template answers. VCAA seems to really like them in differentiating students.

Not 100% sure for that one sorry, not really good with the newton law explanation questions myself. But it definitely sounds right.  Might have to wait for PB and lxnl .

You're definitely right about the dot point template. The first thing our physics teacher told us this year was to make all our explanation answers in dot point form and make templates throughout the year. VCAA examiners love dot points + it really shows that you have great understand of the topic, and you're not just writing long body paragraphs with a lot of bull-crap like the rest of the state

[Yacoubb]

Not 100% sure for that one sorry, not really good with the newton law explanation questions myself. But it definitely sounds right.  Might have to wait for PB and lxnl .

You're definitely right about the dot point template. The first thing our physics teacher told us this year was to make all our explanation answers in dot point form and make templates throughout the year. VCAA examiners love dot points + it really shows that you have great understand of the topic, and you're not just writing long body paragraphs with a lot of bull-crap like the rest of the state

Thanks anyway And yeah, I thinking employing formulae is also helpful. It shows that you can make associations to formulae, and not merely memorising them for the sake of it.

[PB]

Hey Yacoubb,
That explanation seems fine but yes, like you said as well, it would be wise to prove your arguments using formulae. An example of how I might answer is:
-Crumple zones increase the duration of the impact.
-As t increases, a decreases (a=v/t)
-As a decreases F decreases because m stays the same (F=ma)
-Thus, less average force is exerted on the crash victims, minimising injuries.

[Yacoubb]

The actual AC generator consists of 100 turns of wire in a square loop with the length of the sides of the square being 10cm. The strength of the magnetic field is 1.0T. The generator rotates at a frequency of 5 Hz.

What is the magnitude of the average emf induced as the coils turn from perpendicular to parallel to the field?

Using Faraday's Law, it is nBA/t = 100 * 0.01/t = 1/t

Now, using 1/t = frequency, 1/5 = t. However, the solutions indicate that t = 1/20. Could someone explain why this is so? Your help is much appreciated.

[Zealous]

Now, using 1/t = frequency, 1/5 = t. However, the solutions indicate that t = 1/20. Could someone explain why this is so? Your help is much appreciated.

Even though the frequency of the generator is 5Hz, this does not mean that you substitute t=1/5 into Faraday's Law.



Have a look at the two positions above. The first is where there is 0 magnetic flux threading the coil (parallel to magnetic field), while the second shows a position of maximum magnetic flux through the coil. Imagine the coil rotating in a clockwise direction. It can be broken up into four different motions (to simplify it):
1: Rotating from 0 to 90 degrees, going from 0 magnetic flux to maximum magnetic flux. (This is a quarter of a rotation and hence 1/20th of a second)
2: Rotating from 90 to 180 degrees, going from maximum magnetic flux back to 0 magnetic flux.
3: Rotating from 180 to 270 degrees, going from 0 magnetic flux to maximum magnetic flux.
4: Rotating from 270 degrees to 360 degrees (originally position), going from maximum magnetic flux back to 0.

So to find the average EMF induced, we can just take one of these sections of the motion and use 1/20th of a second - that is it takes 1/20th of a second for the coil to go from 0 flux to maximum magnetic flux (or vice versa). You could also use 4 times the magnetic flux (as it goes from a maximum to 0 four times in the motion) with 1/5th of a second if that suits you.

[Yacoubb]

Thanks Zealous really appreciate that.

Just confirming - so is it always multiply 1/t * 4?? I'm really confused, and appreciate your patience. Just don't quite get that little bit. Is it 1/20th by default, or ..?

Thanks

[Zealous]

Just confirming - so is it always multiply 1/t * 4?? I'm really confused, and appreciate your patience. Just don't quite get that little bit. Is it 1/20th by default, or ..?

I probably could've explained the last bit better haha. As a general rule (may not always work!!!), if you are given the frequency F, the delta time (change in time) you put into Faradays Law is 1/(4f) which is one quarter of the period. This is because it only takes a quarter of a period for the magnetic flux to change from zero to a maximum. From a calculus view, it's the average rate of change of the magnetic flux with respect to time.

[Yacoubb]

Hi guys I have a question, and assistance with this would be much appreciated.

1. Explain how a beam of electrons can be used to investigate the atomic structure of metals?

[lzxnl]

Beam of electrons => waves => choose right momentum, can diffract through gaps in metal crystals => diffraction pattern => get distances between metal ions

[Yacoubb]

Beam of electrons => waves => choose right momentum, can diffract through gaps in metal crystals => diffraction pattern => get distances between metal ions

Legend! Thank you so much!