Post your Physics questions here. (2 Viewers)

[lusiv]

put I=100 and d=100 into teh equation

Still don't get0 how to get K... :S

 

[AAEldar]

We know that when I=100, d=100 so we can use these values to find k.





Now when d=200,

 

[Fizzy_Cyst]

Alternately, as some people find the whole concept of 'k' a bit hard to understand, you can use the following:

 

[clementc]

Why do you need to find k?! This is a normal proportionality question.
So intensity varies with , where r is the distance from the source. You can write this as . Say that r is the 100km from the source, so the intensity there is proportional to 1/r^2 ().

So since (to 200km), then the new where I_0 is the original intensity.

So it's a quarter of it's initial strength, so 25.

 

[smilingface]

anyone know how to find direction of eddy current? thats so confusing....especially when you need to describe whether its clockwise or anticlockwise >.< how can you use your right hand thumb to work out~~~ thanks in advance

 

[FCB]

Use the right hand cork screw rule and the thumb is the direction of current and the fingers curl to show the direction of the current

 

[smilingface]

Use the right hand cork screw rule and the thumb is the direction of current and the fingers curl to show the direction of the current

ohhh i thought thumb is the direction of the magnetic field…@.@
thanks

 

[Aclipse]

When explaining superconductivity,

Do I need to know about phonons?



Also, can you explain how Braggs used X-ray to do find out about the lattice structure of things


just need to know enough to answer hsc questions...

 

[Uzername]

The answer is 2.4A, but could someone explain how to get this please.

 

[cheezcake]

Do you know the length of the conductors in the field?

 

[cheezcake]

When explaining superconductivity,

Do I need to know about phonons?



Also, can you explain how Braggs used X-ray to do find out about the lattice structure of things


just need to know enough to answer hsc questions...

Okay first things first, the superconductivity explanation given in the HSC is absolute bullshit. Our teacher says it doesn't even obey the law of conservation of energy. But yes you should talk about phonons or at least mention them as lattice vibrations.

The Braggs' proposed that X-rays due to their short wavelength could penetrate the surface of matter and be reflected by the atomic planes in the matter. They then used collimated X-ray beams to strike the sample under investigation, these x-rays were then scattered from adjacent atomic planes in the crystal. As they scattered, x-ray beams interfered constructively and destructively with another producing a regular pattern. The Braggs used an ionisation chamber to detect the scattered beams position and intensity, from this they were able to measure the angles at which the beams were reflected and hence were able to calculate the spacing and atomic planes within the crystal which they found to be a regular lattice structure. => ULT BASIC EXPLANATION

 

[Uzername]

Do you know the length of the conductors in the field?

No, that's all they give you. It's a multiple choice question from a CSSA paper. In the marking criteria it was also mentioned as a band 5/6 question...

 

[cheezcake]

Mind posting the various answers?

 

[jangbang69]

The answer is 2.4A, but could someone explain how to get this please.

Hey uzername, they give you a force per metre so you need to use force per length: (f/l)=(kII/D)
you can get the answer that way

so its I = root of (5.76x10^-6 x 0.2 / 2;10^-7) = 2.4 A

 

[cheezcake]

Woops, need to read the question more carefully haha. And yeh that should work then

 

[rrlm910]

a) Outline the relationship between Bohr’s atomic model and Planck’s equation E = hf.

Can anyone help? I just dont understand how I should be explaining this.

 

[o_0]

basically, you should talk about how bohr based his model of the atom around planck's hypothesis; that energy is quantised. Bohr's second postulate states that when an electron moves up an orbit level, it absorbs a quanta of energy, and when the electron transits down, it emits energy (in the form of EMR). The energy absorbed/released is proportional to the frequency of the emr, i.e E=hf.

Also, Bohr's first postulate states that electrons remain in discrete stationary orbits without emitting energy, that is, the principle energy shells are quantised (building on Planck's hypothesis)

8)

edit: you could also mention Bohr's third postulate which states that the angular momentum of the electrons is quantised as mvr = nh/2Pi, but that can be explained better with de Broglie's matter wave model

 

[rrlm910]

^ Thanks heaps! So much easier to understand than the sample answer on board of studies Appreciate it!

 

[clementc]

You don't need the common length of the conductors.

or something yeah? I just called the current I because the question gives that both have the same magnitude.

(I like calling k as because it avoids confusion - in the normal ampere force law k=1x10^-7 instead, and then you have k for a billion other things)

BUT ANYWAY

So the force per metre is given as 5.76 x 10^{-6} N. What does force per metre mean? It's the same as F/l

So that means
Rearranging that, you can solve for I^2, and hence I. Remember that d = 0.2m, using SI UNITS!!

 

[chevlr]

You don't need the common length of the conductors.

or something yeah? I just called the current I because the question gives that both have the same magnitude.

(I like calling k as because it avoids confusion - in the normal ampere force law k=1x10^-7 instead, and then you have k for a billion other things)

BUT ANYWAY

So the force per metre is given as 5.76 x 10^{-6} N. What does force per metre mean? It's the same as F/l

So that means
Rearranging that, you can solve for I^2, and hence I. Remember that d = 0.2m, using SI UNITS!!

clementc??? is this who i think it is??? i don't think you need to give olympiad answers to these noobs