Physics Pop Quiz

nedward

Hardly an original idea, but the exam is on Monday, and if it helps...


Give three factors affecting the capacitance of a parallel plate capacitor.

Tomlowe

distance between plates
permittivity of the medium between them
area of plates

three leptons and one property common to all leptons

or

one contribution made by nicholas callan

microbiek

permitivity and distance and dielectric?

sternn

nedward wrote:

Give three factors affecting the capacitance of a parallel plate capacitor.

Distance between the plates
Area of plates
Material that the plates are made of

State Newtons 2nd law

microbiek

too slow damn haha and wrong!!!

JC 2K3

Area of overlap of the plates.
Distance between the plates.
Permittivity of the medium between them.(dielectric)

At B the sound intensity of a source is double the intensity at A. What is the difference in the sound intensity level between A and B?

microbiek

3db

microbiek

distinguish between tranverse an longitudinal waves

JC 2K3

Tranverse Waves oscilate perpendicular to the plane of their direction.
Longditudal Waves oscilate parallell to the plane of their direction.

mathew

tomelowe wrote:

three leptons and one property common to all leptons

The electron, the negative muon and the negative tau.
All leptons are fundamental particles, ie they cannot be broken down into smaller particles.

define the ampere

JC 2K3

1 A = current in 2 infinitely long conductors with negligible cross section 1 m apart that put a force of 2*10^-7 N on each other in a vacuum.

Explain how a depletion layer is formed in a PN Junction.

tolosenc

Holes move from P->N, and an equal number of electrons form N->P, or some such. Right?

Why is Coulomb's Law an example of an inverse square law?

eZe^

Because the resultant force is proportional to the square of the distance between the point charges.....



Describe an experiment to find the critical angle of a medium.

microbiek

state keplers 3rd law

carlowboy

microbiek wrote:

state keplers 3rd law

Not on the syllabus

Why is Coulomb's Law an example of an inverse square law?

Force is proprtion to 1 over the square of the distance (I'm translating from irish to english so apologies for the poor wording.)

Tomlowe

critical angle of a solid medium

put block of medium on a white piece of paper. place two pins at an angle to the medium and look through from the other side of the medium. find the line on which the further pin is hidden behind the nearer and insert two pins on that line

trace around the medium, and find the tangents at the point of contact of the medium and the rays (if the medium is irregularly shaped)

draw normals perpendicular to these tangents

draw the lines which the pins are on, and connect the points at which they meet the medium. find the angles of incidence and refraction using a protractor. Find Sin(i)/Sin(r). this is the refractive index n. the inverse sin of 1/n is the critical angle C.



Why does a metal covered by a piece of ordinary glass not emit electrons when incident photons are above the threshold frequency?

(i actually dont know that one)

eZe^

Tomlowe wrote:

critical angle of a solid medium

put block of medium on a white piece of paper. place two pins at an angle to the medium and look through from the other side of the medium. find the line on which the further pin is hidden behind the nearer and insert two pins on that line

trace around the medium, and find the tangents at the point of contact of the medium and the rays (if the medium is irregularly shaped)

draw normals perpendicular to these tangents

draw the lines which the pins are on, and connect the points at which they meet the medium. find the angles of incidence and refraction using a protractor. Find Sin(i)/Sin(r). this is the refractive index n. the inverse sin of 1/n is the critical angle C.



Why does a metal covered by a piece of ordinary glass not emit electrons when incident photons are above the threshold frequency?

(i actually dont know that one)

Ordinary glass doesnt transmit UV rays so the work function of the metal would not be overcome by the energy of the incident photon...


Btw, with the critical angle experiment make sure the medium is a hemisphere, not a block, because otherwise the light will never be able to enter the normally and be bent properly.

Tomlowe

medium doesnt have anything to do with the shape of it... refractive index for a square block of glass is the same as a circular, cubic, elliptoidical, whatever block of the same glass

do we not get a question from you?

carlowboy

I'll start again. Derive F=QVB

That's on the syllabus isn't it?

eZe^

Tomlowe wrote:

medium doesnt have anything to do with the shape of it... refractive index for a square block of glass is the same as a circular, cubic, elliptoidical, whatever block of the same glass

do we not get a question from you?

Im talking about critical angle, a special specified activity on the syllabus though. Not the refractive index question... oh ya, em...



State the laws of electromagnetic induction.

Tomlowe

Faraday - The electromotive force is proportional to the rate of change of magnetic flux linkage

lenz - The induced emf acts in such a way as to oppose the action inducing it.

Im pretty sure the derivation of bvq isnt on the syllabus, at least i hope it isnt...

Define Power.

carlowboy

Work done over time.

Oh and derive s=ut +at^2/2

eZe^

Tomlowe wrote:

Faraday - The electromotive force is proportional to the rate of change of magnetic flux linkage

lenz - The induced emf acts in such a way as to oppose the action inducing it.

Im pretty sure the derivation of bvq isnt on the syllabus, at least i hope it isnt...

Define Power.

Work done per unit time... bnqv derivation is on the syllabus, its very easy though...

take a current carrying conductor of lenght L in a magnetic field of flux density B...

I = nq/t and v = d/t (where v linear speed of charges)
v = L/t
L = vt


F = BIL
F = B (nq/t)(vt)
therefore, F = Bnqv....
for one charge, n = 1


F = Bnqv.

Derive the 3 accelerated linear motion equations.

eZe^

carlowboy wrote:

Work done over time.

Oh and derive s=ut +at^2/2

v = u + at
ds/dt = u + at
Integral ds = Integral u +at dt
s = ut + at^2/2 + c
when t = 0, s = 0, therefore c = 0..

therefore s = ut + 1/2 (at^2)


Derive the other 2.

Tomlowe

s = Integral(v)dt
v = Integral(a)dt

Integral(a)dt
= at + c
= v (acceleration is taken to be a constant)

let t=0 => c=u since u is initial velocity

Integral(v)dt
=Integral(at + u)dt
=1/2at^2 + ut + c

let t=0
=>c=0 as initial displacement is zero

therefore
s = ut + 1/2at^2

Tomlowe

damn, i hate my life

JC 2K3

carlowboy wrote:

I'll start again. Derive F=QVB

That's on the syllabus isn't it?

Yes, but the derviation in the book is ridiculous.

In a conductor with charge, q, flowing with speed v ina magnetic field with flux density B:
F = BIl
I = q/t
l = vt
F = Bqvt/t
F = qvB

cocoa

eZe^ wrote:

Btw, with the critical angle experiment make sure the medium is a hemisphere, not a block, because otherwise the light will never be able to enter the normally and be bent properly.

<annoying pedant>actually, it is still possible, it's just a major pain to set up.</annoying pedant>
of course, that is totally irrelevant and in an exam (or anywhere else) it is definitely a good idea to use the 'ole hemispherical block.

eZe^

cocoa wrote:

<annoying pedant>actually, it is still possible, it's just a major pain to set up.</annoying pedant>
of course, that is totally irrelevant and in an exam (or anywhere else) it is definitely a good idea to use the 'ole hemispherical block.

Could you explain to me how? Because I was arguing with my physics teacher that there definitely must be another way, and he was saying that other shapes would mean it can only enter normally one way, therefore you would have to have loads of different shapes to find the critical angle. I lost the argument!

carlowboy

eZe^ wrote:

v = u + at
ds/dt = u + at
Integral ds = Integral u +at dt
s = ut + at^2/2 + c
when t = 0, s = 0, therefore c = 0..

therefore s = ut + 1/2 (at^2)


Derive the other 2.

a= rate of change of velocity so
a v/t-u/t
at=v-u
v=u +at

v= u +at
square both sides
v^2= u^2 +2uat+(at)^2
.....= u^2 +2a(ut +at^2/2)
v^2= u^2 +2as

Is mine too simplistic?

JC 2K3

I presume you just measure the angle differently? Like, the angle you shine the ray at the block at would not be C, but you could get C from that...

EDIT: Or actually, yeah, could you not just mark where the ray enters and make sure the incident ray hits a point under which you've already marked and connect em, then get C like that?