IB Physics help

guys it would be great if we could help each other with Physics, whether it's at GCSE level, IB or A-levels.
I'm struggling loads after all so I think team-work and support is the best solution, not only for me but for you too!
After all, teaching is the most efficient way to learn!

Reply 1

Levi23317

15

What do you need help with.

Reply 2

mikaelalrc

OP

8

hi!! hahah everything, but with the waves topic to start with, I guess. It's mostly applying my knowledge to practice questions that I find the hardest, I think.

Original post by Levi23317

What do you need help with.

Reply 3

Levi23317

15

If theres any questions you want help with im happy to help

Reply 4

mikaelalrc

OP

8

Hi,
I don't understand the inverse square law - at all. Like I get that it means that if the distance doubles then the intensity quadruples or something idk but... Any help please?

Original post by Levi23317

If theres any questions you want help with im happy to help

Reply 5

Levi23317

15

Original post by mikaelalrc

Hi,
I don't understand the inverse square law - at all. Like I get that it means that if the distance doubles then the intensity quadruples or something idk but... Any help please?

So the inverse square law in terms of intensity refers to the power per unit area from a a wave source that is emitting waves equally in all directions. So if you picture an expanding sphere whos centre is the wave source e.g core of a star, it expands, so the power for a given area decreases the further away you are since the sphere is larger. Since its a sphere the intensity (power per unit area) is p/4piR^2 , as 4piR^2 is the surface area of a sphere. Therefore intensity is inversely proportional to the separation from the centre of the source (radius) squared.

Reply 6

username4697360

16

The waves topic is a personal favorite of mine! If you have any questions send them :smile:

Reply 7

Levi23317

15

Original post by JasmineLLB

The waves topic is a personal favorite of mine! If you have any questions send them :smile:

Yo me are we like best friends or somethin

Reply 8

mikaelalrc

OP

8

Thank you! But I still don't quite understand it... It's the maths that confuses me. And what does inversely proportional mean again?

Original post by Levi23317

So the inverse square law in terms of intensity refers to the power per unit area from a a wave source that is emitting waves equally in all directions. So if you picture an expanding sphere whos centre is the wave source e.g core of a star, it expands, so the power for a given area decreases the further away you are since the sphere is larger. Since its a sphere the intensity (power per unit area) is p/4piR^2 , as 4piR^2 is the surface area of a sphere. Therefore intensity is inversely proportional to the separation from the centre of the source (radius) squared.

Reply 9

Sinnoh

22

Original post by mikaelalrc

Thank you! But I still don't quite understand it... It's the maths that confuses me. And what does inversely proportional mean again?

Y is inversely proportional to X:

Y = \dfrac{k}{X}

where k is some constant, doesn't matter. So as X gets bigger, Y gets smaller - because you're dividing by a bigger number.
So if X is made twice as big, Y is made half the size.

Y is inversely proportional to the square of X - aka inverse-square relationship:

Y = \dfrac{k}{X^2}

Same rule - as X gets bigger, Y gets smaller - but it happens a lot quicker. So if X doubles, Y is reduced 4 times. If X is tripled, Y is reduced 9 times. Substitute 3X and square it, and you'll see.

Y is directly proportional to X: