Prelim Physics Thread (3 Viewers)

[jathu123]

Why would moving at a constant velocity imply zero acceleration?

acceleration basically means change in velocity, if the velocity is constant then there is no change, hence no accelration

 

[eyeseeyou]

note: ΣF=ma is the same thing but this one implies net force. But yeah the answer should be obvious now..

Why would (sigma)F=ma imply net force?

 

[cookie_dough]

sigma means net

 

[porcupinetree]

Oh yeah, where is F=MA derived from?

The equation ΣF=ma (where ΣF and a are vector quantities pointing in the same direction), which is one way to write Newton's 2nd law, isn't as much derived from other equations/laws, rather, it provides a definition of net force - i.e. if an object is accelerating, then there is a net force acting upon the object. It's a fundamental law.

In fact, Newton didn't specifically specify the equation F=ma to be his 2nd Law. Rather, Newton wrote:

That is, the net force on an object is the time derivative of its linear momentum. This can be rearranged as follows to form the more familiar expression for Newton's 2nd law:

 

[InteGrand]

Why would (sigma)F=ma imply net force?

ΣF stands for the sum of all forces, which is by definition the net force (which is also what the "F" in "F = ma" stands for).

 

[Green Yoda]

Bump!
A simple question to start of again:
Describe one application of a concave reflecting surface. (3)

 

[Green Yoda]

A question I need help with:
What would happen to the intensity of light from a lamp if the intensity at the source were to half and the distance were to triple?

 

[Green Yoda]

BUMP

 

[InteGrand]

A question I need help with:
What would happen to the intensity of light from a lamp if the intensity at the source were to half and the distance were to triple?

(See: https://en.wikipedia.org/wiki/Inverse-square_law#Example )

 

[Green Yoda]

Bump!
A simple question to start of again:
Describe one application of a concave reflecting surface. (3)

No one answered lel

Radio Telescopes are an example of an concave reflecting surface as they collect incoming parallel signals from the distant and concentrate the signal by reflecting it to a single focus area where the aerial is located in which the data is detected and processed.

 

[eyeseeyou]

No one answered lel

Radio Telescopes are an example of an concave reflecting surface as they collect incoming parallel signals from the distant and concentrate the signal by reflecting it to a single focus area where the aerial is located in which the data is detected and processed.

Do you have the marking criteria?

 

[Green Yoda]

Do you have the marking criteria?

I think so but the marking criteria talks about the torch but I have researched Radio Telescopes for my notes.

 

[Nailgun]

No one answered lel

Radio Telescopes are an example of an concave reflecting surface as they collect incoming parallel signals from the distant and concentrate the signal by reflecting it to a single focus area where the aerial is located in which the data is detected and processed.

not sure if srs answer but pls dont try and answer a 3 marker with 1 sentence (although pree good sentence)

 

[Green Yoda]

not sure if srs answer but pls dont try and answer a 3 marker with 1 sentence (although pree good sentence)

Yeah I did fill up all the space given tho
Yeah I know it is not much info there but that's all I could find about the application of reflection in the radio telescopes.

 

[Green Yoda]

Outline one application of the Ionosphere for a particular EM wave.

 

[Green Yoda]

Outline one application of the Ionosphere for a particular EM wave.

The ionosphere reflects a percentage of radio waves which are sent back towards the Earth. This allows the information in the radio waves to be sent over long distances.

 

[Green Yoda]

Quick question
For the dot point:
Outline how total internal reflection is used in optical fibres

I have written:
The optic fibres have 2 layers of glass with the reflective index of the outer layer less than the inner layer. Therefore when light enters the optic fibre it is internally reflected between the outer and inner layers and continues moving forward within the optic fibre instead of escaping through the surface.

Does this correctly answer the dot point? I'm quite unsure if I am missing any other information.

 

[leehuan]

From memory the main thing with total internal reflection is basically that because the ratio of refractive indices is so large the ray ends up bouncing back in. I don't remember finer details.

 

[jathu123]

Along with the different refractive index, I think you should also mention the other requirement for total internal reflection, that the angle of incidence must be greater than the critical angle.

 

[Green Yoda]

Along with the different refractive index, I think you should also mention the other requirement for total internal reflection, that the angle of incidence must be greater than the critical angle.

Critical angle is also defined as:
The critical angle is the angle where total internal reflection prevents the ray from escaping from a higher optical-density medium to a lower optical-density medium.

In my answer I have stated that the refractive index of the inner layer is higher than the outer layer thus being more dense which prevents the light from refracting so the angle of incidence exceeds the critical angle which is assumed by the previous statements.