Physics: A Bitch of an exam

irishbucsfan

Thats right. Its horrible, disgusting and even a little bit perverse.

I spent all day today studying for it and Ive made very little progress (Im thinking of ordinary...)

And so to make things interesting Ive invented something. Something revolutionary and exciting. I call it:

A Quoz. The name might need a little tinkering but I think I like Quoz.

So in a Quoz what happens is this, a question is asked, and then the next person answers.

Here are the rules. If you want to ask a question, you must answer the on above, or make an attempt at it. You may ask for help at any stage.

Lets say... Person who gets the most questions right gets a prize, selected by the Quozmaster (me).

If you dont do physics then you're inelligible, find your own quoz. I know who you are and how to find you and if you sabotage my quoz ill get you.

I'll start things off with some nice easy mechanics:

A force of 2400N causes a car to accelerate from rest to a speed of 20 m/s^-1 in 10 seconds.  Calculate (i) the mass of the car, (ii) the distance travelled by the car in the first 10 seconds

nyangnyang

1200kg and 100m

DemocAnarchis

A force of 2400N causes a car to accelerate from rest to a speed of 20 m/s^-1 in 10 seconds. Calculate (i) the mass of the car, (ii) the distance travelled by the car in the first 10 seconds

.

Is m/s^-1 not redundant? Works out as m.s or metre second. You mean m.s^-1 or m/s

I think providing worked answers is probably more condusive to learning, so...

(i) Force = Mass x Acceleration

A = (Vx-V0)/(Tx-T0)

Vx = 20m/s
V0 = 0m/s
Tx = 10s
T0 = 0s

A = (20m/s-0m/s)/(10s-0s) = (20m/s)/(10s) = 2m/s^2

F = 2400N
M = y
A = 2m/s^2

2400N = y.2m/s^2

.: (2400 kg.m/s^2)/(2m/s^2) = y

Mass of car y = 1200kg

(ii)

s = ut + 0.5at^2
v^2 = u^2 +2as

U = Initial Velocity
V = Final Velocity
T = Time taken
S = Distance Travelled
A = Acceleration

U = 0m/s
V = 20m/s
T = 10s
S = ?
A = 2m/s^2

We can use either formula to solve for s. The first has less squaring so less hassle.

S = 0m/s.10s + 0.5(2m/s^2.((10s)^2))
= 0 + 0.5(2m/s^2.100s^2)
= 0 + 0.5(200m)
S = 100m


Way way oversimplified for an easy question, but meh :pac:

Cokehead Mother

Two people answered and nobody asked a question sooo...

Derive the formula v = fλ (technically not on the syllabus but can be done easily enough with LC physics knowledge).

kaki

Speed = Distance / Time

Frequency = 1 / Time
therefore Time = 1 / Frequency

Speed = Distance / (1 / Freqency)

So speed = Distance x Frequency
Distance= one wavelength=λ

v=λf

Is that okay?

If so...someone hit me with an equation to represent the Cookroft and Walton exp....

Cokehead Mother

7_3 Li + 1_1 p -> 4_2 He + 4_2 He + energy

What's the quark structure of a proton?

starkinter

Cokehead Mother wrote: »

What's the quark structure of a proton?

u u
d

Who proposed the neutrino?

Decerto

wolfgang pauli proposed it fermi named it the little neutral one,
explain string theory!

devinejay

String theory - All sorts of crazy jabberwocky that explains why light is both particles and a wave motion. How does this theory achieve this you ask? Cause the guys who made it up seem to know what they're on about.

Explain/differentiate between a Geiger Muller tube and a solid state detector.

mike-gunners

quark structure of proton:uud(up up down)
neutron:udd
the charges of quarks:up=2/3, down=-1/3, strange=-1/3, charmed=2/3, bottom=-1/3, top=2/3.
so it makes sense to say that proton has +1 charge because:uud=2/3 + 2/3 - 1/3 = 1.
similarly, neutron has 0 charge because:udd= 2/3 - 1/3 -1/3 = 0.
the anti-quarks of these 6 quarks are given with a "dash" on top of them.an anti-quark has a reversed charge of a quark eg if "U" is a quark of charge 2/3, then anti-quark of U has a charge of "-2/3".
if u have any questions about other topics in physics, post em.

mike-gunners

starkinter wrote: »

u u
d

Who proposed the neutrino?

wolfgang pauli proposed the neutrino.he observed the following:he observed a beta decay reaction and found out that mass and momentum both were not conserved.this led him to believe that a small particle existed and , when he took this into account, he found that both momentum and mass were conserved.

irishbucsfan

devinejay wrote: »

Explain/differentiate between a Geiger Muller tube and a solid state detector.

In a Geiger/Muller tube, the detecting medium is often Argon gas, whilst in a Solid State detector a semiconductor material such as silicon or germanium is often used.

Define Faraday's Law and Lenz's Law

Cokehead Mother

Faraday's law states that enduced emf is proportional to the rate of change of the magnetic flux.

Lenz's law states that the change in flux is such to oppose the force that caused it... I think?

A man is walking away from a speaker at a speed of 2 m/s. The man appears to hear a note of frequency 480Hz coming from said speaker. Taking the speed of sound to be 330 m/s, calculate the actual frequency of the note and its wavelength.

devinejay

480 = f(330)/330+2

f = 482.9 Hz

c = f(lambda)
330 = 482.9 (wavelength)
wavelength = 0.68 m


State Einstein's Photoelectric law

Cokehead Mother

hf = h x threshold frequency + 1/2 mv^2

A current of 6A is flowing through a copper wire of length 5m and diameter 3mm. Find the voltage.

(The resistivity of copper is 1.72×10−8 Ωm)

Decerto

R= pxl/A, R = 1.72x10^-8 x 5/ pi(1.5x10^-3)^2
= .0123 ohms

v=ir
v .0123x6= .073V

dnno if thts right?

List the force carrier particles for the 4 fundamental forces(assuming gravitys one is real)

powpeach

Strong nuclear
weak nuclear
gravitational force
electromagnetic force


i think!

this is from q11 2006. may need to read the paragraph first but

Why must the strings of an electric guitar be made of steel?

i never got a chance to ask my teacher if this was correct:
Becase steel contains iron and the iron causes the magnetic field to change. thus inducing an emf!:cool:

Decerto

powpeach wrote: »

Strong nuclear
weak nuclear
gravitational force
electromagnetic force


i think!

this is from q11 2006. may need to read the paragraph first but

Why must the strings of an electric guitar be made of steel?

i never got a chance to ask my teacher if this was correct:
Becase steel contains iron and the iron causes the magnetic field to change. thus inducing an emf!:cool:

The particles which carry the forces not the forces themselves:)

Cokehead Mother

Photons carry the electromagnetic force
Graviton carries the gravitational force
Gluons carry the strong force
Bosons carry the weak force

(btw if anyone is freaking out, I don't think this is on the LC course)

I'm pretty sure what you've said about iron is fine, powpeach.

Give an equation for pair production and pair annihilation.

pocket aces

pair production: hf -> 2mc^2 + Ek1 +Ek2

pair annihilation: (E+) + (E-) -> 2hf

Define the ampere (worst definition :pac:)

fivetwenty

A current value which produces a force of 2x10(-7) Newtons on each conductor provided they are of infinite length, negligeble CSA, 1m apart in a vacuum and parallel.

Derive the relationship between Periodic Time & Radius in reference to a satellite . . .

starkinter

F = mv²/r
F = GMm/r²

mv²/r = GMm/r²
v² = GM/r
v = √(GM/r)

P = 2πr/v
= 2πr/√(GM/r)
= 2πr√(r/GM)
= 2π√(r³/GM)

I assume that's what you were looking for...

Define specific latent heat of fusion.

A-Bit-Dodge

Specific Latent heat of fusion is the amount of heat needed to bring one kg of a substance from solid state to liquid state without change in temperature.


List the three factors wich affect the capacitance of a parallel plate capacitor
...

Cokehead Mother

The area of the plates
The distance between them
The permitivity of the substance between them

State two differences between gravitational force and electromagnetic force.

A-Bit-Dodge

Cokehead Mother wrote: »

The area of the plates
The distance between them
The permitivity of the substance between them

State two differences between gravitational force and electromagnetic force.

1)Gravitational only affects very large masses and is always attractive
2)Electromagnetic affects all sizes and can be attractive OR repulsive.

What is the energy change that occurs in a n motor?

Decerto

kinetic to electric or is that a dynamo?,
and the capacitance question its common area between the plates,

whats the difference between mutual induction and self induction?

Cokehead Mother

Self induction is when the emf of a coil changes because of a change in the magnetic flield of said coil.

Mutual induction is when the emf of a coil changes because of a change in the magnetic field of another coil.

A car is moving at a constant speed of 18 m/s against air restance of 3000N. What is the power output of the car?

acidstorm

A-Bit-Dodge wrote: »

1)Gravitational only affects very large masses and is always attractive
2)Electromagnetic affects all sizes and can be attractive OR repulsive.

What is the energy change that occurs in a n motor?

Electric to kinetic




Mutual Inductance occurs when a changing emf in a conductor induces an emf in a nearby conductor while self inductance occurs when the change in emf in a conductor causes a back emf which opposes the emf change in that same conductor (Lenz Law Anyone?) I stand to be corrected

Decerto

power = fv
=54000J/s?,
explain why a thermistor's resistance decreases when it heats up

Cokehead Mother

A thermistor is a semi-conductor. As it is heated, more energy is supplied to it, more outer electrons are freed for conduction and thus resistance decreases.

What does the quality of a sound depend on?

kaki

Frequency - Pitch
Wavelength - Amplitude
Harmonics - Overtones

Archimedes principle states...

Cokehead Mother

A body immersed in a liquid experiences an uptrust equal to the weight of the liquid displaced.

How can an accelerating particle have a constant speed?

kaki

If it's undergoing circular motion, it will always experience an accelerating force towards the centre, yet it's instanteous velocity will remain constant.

Describe and explain the shape of an I/V graph for a vacuum.

acidstorm

Cokehead Mother wrote: »

A body immersed in a liquid experiences an uptrust equal to the weight of the liquid displaced.

How can an accelerating particle have a constant speed?

When the body moves in a circle the magnitude of the velocity (speed) is the same but the direction is changing.

An experiment to explain the photoelectric effect?

kaki

Experiment: Charge an electroscope by induction positively by induction, place on top of a gold leaf electroscope, allow UV light to fall on the zinc sample, and watch as the gold leaves converge...

I won't ask another question yet

Cokehead Mother

I've never come across the I-V graph of a vacuum before so this may all be very wrong but...

Vaccum's are completely empty so there's no charged particles and hence they're total insulators. So I is just going to be 0... because V = IR and R = V/I then I being 0 would make R tend towards infinity which is what a 100% insulator type thing would have? So basically it's just going to be a straight line along the x-axis... I think?

Distinguish between intrinsic and extrinsic semiconductors.

kaki

Re the graph for a vacuum: You'd think it's 0 alright, but if the cathode gets hot enough, thermionic emission occurs, and electrons travel across the tube. As the p.d. increases, so does the current, until all possible electrons have been emitted, and it levels off.

Intrinsic conduction = Conduction in a pure semiconductor due to electrons moving from negative to positive, and an equal number of holes moving in the opposite direction. Extrinsic conduction = the increased conduction of a semi-conductor due to doping (addition of controlled amounts of impurities).

Q: Explain magnetic variation

kaki

Crappy illustration of IV graph for vacuum

cartman444

hey i just cant seem to get my head round how a rocket works!lol

it says in my book the burning gas has a very high velocity so a large momentum and therefore the rocket has an equal and opposite momentum in the other direction. but if the momentii() are equal then in opposite directions does that not mean they cancel each other out and it shouldnt move!!

acidstorm

cartman444 wrote: »

hey i just cant seem to get my head round how a rocket works!lol

it says in my book the burning gas has a very high velocity so a large momentum and therefore the rocket has an equal and opposite momentum in the other direction. but if the momentii() are equal then in opposite directions does that not mean they cancel each other out and it shouldnt move!!

I think you forgot Newton's third law--> To every action, there is an equal but opposite reaction. So If the gas is being pushed out, the gas molecules kinda push the rocket the other way.

Think of this--> When you stand on the floor, there is a force pushing against your feet and obviously, a force pushing down on the floor , hence your knees start to hurt if you stand for too long. the force is equal to your weight, thats why you dont fly off the surface of the earth, however, a rocket on the launchpad for example blasts out so much more force than its own weight, hence it moves forward.

Hope this helps

acidstorm

kaki wrote: »

Q: Explain magnetic variation

This is the difference between the geographical north and the magnetic north. I actually know this as angle of declination and I had to confirm that they were the same thing before I posted

Cokehead Mother

Nobody asked a question soo...

what is the principle on which the definition of the ampere is based and briefly outline an experiment to demonstrate this.

Patrickisperfec

when 2 wires are 1 metre apart and there is a current of 1Amp flowing through them, there should be a force 1.6x10^16 (I think)N against each other.


Not sure about the exp.

Name 2 Mesons

cartman444

acidstorm wrote: »

I think you forgot Newton's third law--> To every action, there is an equal but opposite reaction. So If the gas is being pushed out, the gas molecules kinda push the rocket the other way.

Think of this--> When you stand on the floor, there is a force pushing against your feet and obviously, a force pushing down on the floor , hence your knees start to hurt if you stand for too long. the force is equal to your weight, thats why you dont fly off the surface of the earth, however, a rocket on the launchpad for example blasts out so much more force than its own weight, hence it moves forward.

Hope this helps[/QUOTE

CHEERS!!!! I think I understand now!

acidstorm

Cokehead Mother wrote: »

Nobody asked a question soo...

what is the principle on which the definition of the ampere is based and briefly outline an experiment to demonstrate this.

is that the experiment with the aluminium foil and a block where the two wires have current flowing in opposite directions. the wires move away from each other. I hope no one has answered it already

How is the ice dried in the latent heat of fusion experiment..

salman85

acidstorm wrote: »

How is the ice dried in the latent heat of fusion experiment..

crushed using pestle + mortar, dried using a tissue

explain how momentum is conserved in beta decay

acidstorm

salman85 wrote: »

crushed using pestle + mortar, dried using a tissue

explain how momentum is conserved in beta decay

By the introduction of the neutrino?

What are cathode rays

cartman444

cathode rays are rays/streams of high speed electrons.

1.they can be deflected by magnetic and electric fields.
2.they have a negative charge.
3.they are used in tv's to produced images.

how does they geiger/muller tube/counter work?

acidstorm

cartman444 wrote: »

how does they geiger/muller tube/counter work?

They have an anode and a cathode, and connected to a high voltage source. They contain gases at low pressure (Argon esp) When radiation goes into the tube, It ionises the gases, and thus allows the electrons move to the anode, the resulting current can then be connected to a speaker or an LCD to show the count. I personally think of it as electrolysis of a gas lol

Oh and by the way, I think they got it wrong on the No 5 question in this quiz -->http://www.scoilnet.ie/Quiz.aspx?id=698
Who discovered X Rays

blueepurple

rontgen i think.

who invented the cloud chamber?

salman85

blueepurple wrote: »

who invented the cloud chamber?

not on the course.