Physics Marathon! (1 Viewer)

[polyspaston*]

They were doing this for chemistry and business so why not in physics?
Basically, the rules are:
1) Ask a question and allow someone else to answer it
2) Once the question has been answered, the person who answered it must ask another question and let someone else answer it.
3) Questions should be (but does not have to be) exam-style questions.
4) Option questions are allowed but try not to ask consecutive option questions otherwise people doing different options won't get the chance to answer the question.

OKAY... ready steeaddyy.... GO!!

Here's my question:

Discuss the effects of time dilation, length contraction and mass increase for space travel?

 

[wrxsti]

lol. i started the chem thread on this
ok anyways.

Firstly the nearest galaxy towards us is the Andromeda galaxy which is over 10 million light years away.... the nearest star is Alpha Centauri. travelling at half the speed of light would take around 8 years, time dilation and length contraction would make this journey seem relatively quick for Passengers on board, From earths perspective this would still take a very long time.
Althought time dilation amd length contractions work in our favour... relativistic mass increases mean we would need an infinite ammount of fuel to create an infinite force. to acclerate our aircraft which is approaching infinite mass as it approached the speed of light... none of this is physically possible. so travel outside our solar system is not feasible ..

Ok my questions.... i asked this in another thread and didnt get a reply so ill ask it here

2) Discuss Evidence for the particle nature of light (5marks)

 

[thehootman]

The results of the photoelectric effect could only be explained if light carried energy in discrete packets, or quanta. This was direct evidence for the particle nature of light, as each packet of energy could be linked to an individual particle, known as a "photon".
Additionally, black body radiation could not be explained successfully with classical (light as a wave) physics. Classical physics predicted that as the wavelength of the radiation going into the black body decreased, the radiation emitted by the body would increase to infinite amounts. This was in direct contrast to experimental results. When the quantum theory of light being particular was applied to black body radiation, theory was in agreement with experiment. This was further evidence for the particle nature of light.

I havnt studied for physics since the trials so please excuse any wrong things with that answer.

3) A transformer has large insulators on one side, and smaller insulators on the other. Account for the different size of insulators.

 

[Forbidden.]

The results of the photoelectric effect could only be explained if light carried energy in discrete packets, or quanta. This was direct evidence for the particle nature of light, as each packet of energy could be linked to an individual particle, known as a "photon".
Additionally, black body radiation could not be explained successfully with classical (light as a wave) physics. Classical physics predicted that as the wavelength of the radiation going into the black body decreased, the radiation emitted by the body would increase to infinite amounts. This was in direct contrast to experimental results. When the quantum theory of light being particular was applied to black body radiation, theory was in agreement with experiment. This was further evidence for the particle nature of light.

I havnt studied for physics since the trials so please excuse any wrong things with that answer.

3) A transformer has large insulators on one side, and smaller insulators on the other. Account for the different size of insulators.

In a practical transformer, the power output is slightly less than the power input.
i.e almost like P_input = P_output , V_inputI_input = V_outputI_output

(In an ideal transformer, P_input = P_output for sure)

There is greater current on one side than the other according to that relationship.
Additionally according to the equation P = I²R, the power loss is proportional to the current.

There is more current on one side than the other so there are obviously larger insulators on the side with larger current.

That's how I can explain.

Next,
4)

• describe the significance of Einstein’s assumption of the constancy of the
  speed of light

This seems to be an ideal thread to place this so,
I emailed my Physics teacher for some some I2I help,
none of the contents of the email has been modified except in bold, due to a unit error.
(The unit for electric field strength is N/C not J/C)

1. Electric fields
If a question asks "Calculate the electric field strength between two plates with a potential difference of 100V and 10cm apart" I would use E = V/d = 100/0.1 = 100 x 10 = 1000 V/m.

Can I also write 1000 N/C, since the "electric field stregth is defined as the force per unit of charge i.e. E = F/q ?"



Yes:



1 J = 1 Nm Dividing both sides by 1 C gives

1 J/C = 1 N/C * m since 1 J/C = 1 V:

1 V = 1 N/C * m dividing by 1m gives:

1 V/m = 1 N/C



2. Hertz's Experiment
Does the polarisation of the radio waves prove it was an electromagnetic wave ?

No, the Hertz experiment proved that electromagnetic waves existed, which had been predicted from Maxwell's equations, i.e. that soemthing could be produced from changing magnetic and electric fields which had wave properties. These are the original electromagnetic waves, the easiest ones to produce. It had to be shown that light and shorter wavelentgth waves are also EM - waves. The polarisation does follow from Maxwell's equations.



3. Black Body Radiation
At the peaks or maximum points on the Black Body Radiation i.e. Intensity vs. Wavelength graph, does it mean at certain wavelengths, a black body will emit more energy at those certain frequencies ?



Yes, i.e. the black body will emit more photons all of the energy h * f at these wavelengths.

 

[wrxsti]

Significance of Einsteins speed of light as constant

-Spacee and time are relative
All observers see light travelling at 3x10^8
All intertial frames are equivalent.
It also provides explanation on why a Null result was achieved in the Michealson morley experiment.

I thinkk thats right

Question.
What is function of brush?

 

[thehootman]

1)To provide a steady electrical contact onto the commutator/slip ring and pass current through to these.
2) To make the female species feel happier in the knowledge that their hair is neat and orderly.

Explain newton's concept of escape velocity.

 

[wrxsti]

Newtons concept of escape velocity.....
Our good old friend Isaac reasoned that if he were standing on top of a mountain, the further he projected a stone the further it would go, he thus reasoned that there was a velocity at which the object would go into stable orbit and escape the earths gravitational field. hence; escape velocity

By equating Gravitational potential energy and Kinetic Energy equations we can obtain an expression for escape velocity.


Question.

Assess the impact of transistors on society....

lol Nah jokes

Question: Explain how thermionic Devices work

 

[arwin]

In a practical transformer, the power output is slightly less than the power input.
i.e almost like P_input = P_output , V_inputI_input = V_outputI_output

(In an ideal transformer, P_input = P_output for sure)

There is greater current on one side than the other according to that relationship.
Additionally according to the equation P = I²R, the power loss is proportional to the current.

There is more current on one side than the other so there are obviously larger insulators on the side with larger current.

That's how I can explain.


Correct me if I'm wrong, but I think the answer to that question is related to the voltage as opposd to size of current.
The question was
3) A transformer has large insulators on one side, and smaller insulators on the other. Account for the different size of insulators.

-On one side the voltage is larger than the other
-Insulators are necessary to prevent sparks jumping from the transformer to the pole/electric cables
-The ease with which a spark can jump across a gap is proportional to the voltage
-Thus for a larger voltage, a larger insulator is needed to prevent sparks

In answer to the next question, explain how thermionic devices work:
wow this is a hard question but i'll have a go anyway
Diode:
-It uses a glass vacuum tube with an anode on one end and a filament for a cathode
-A heating circuit connected to the filament/cathode heats up the filament and electrons are "boiled" off the filament
-a separate circuit is connected with positive terminal on the anode and negative on the filament, used to either accelerate the electrons to the anode, or stop the electrons
-by varying the voltage across the second circuit, we can make electrons flow or not flow, thus it works as a switching device

Triode:
-same set up as triode but with the addition of a grid, which is just an electrode placed close to the cathode. The grid circuit is connected with positive terminal on the grid and negative on the cathode
-without the grid, electrons flow from the cathode to anode due to the voltage in the anode circuit
-by adjusting the voltage across the grid circuit, it works to either assist or impede the electron flow. So the variations, or signal, in the grid circuit becomes replicated in the anode current. Thus the triode works as an amplifier

Next question: How does Einstein's tehroy of special relativity explain the result of the Michelson Morley experiment? (4 marks)

 

[twilight1412]

The point was that it doesnt =)
im not sure if you know this but einstein's theory of relativity showed how aether wasnt neccessary
the purpose of the MM experiment was so that they could prove the existance of a mythical being called aether which filled all space to allow the propagation of light waves
if the aether existed then we would have what would be called a universal frame of reference against which all measurements could be taken
einstein's relativity relies on the fact that the velocities are measured relative to the observer not a universal reference frame =)

i guess you could say if you needed something to talk about
length contraction along the axial arm of the MM experient which caused the interference pattern to be constructive although we know this is bullshit =)
anyway einsteins equations of length contraction/time dialation were proposed by someone called lorenz to explain the contraction of the arm =)

so you could propose that the arm did indeed contract as far as the aether was concerned .. that is if it really existed =)

btw you have a minor error in your last paragraph =)
it should me 'similar to the DIODE'

ok my question? hahaha
AC motors (not induction) how do they work? we know that australian power supplies works at 50Hz so does this mean that AC motors have to make 25 complete revolutions per sec??



dc motors rely on the commutator to switch the current but thats dependant on the speed at which the motor turns, but with the AC motor since it switches by itself does this mean that the speed is preset at 25 revs a sec?


side note: hahaha man i miss this place =) havent been here in months


EDIT: .......... did i make my question too hard?changed my question slightly to give you guys a better idea of what exactly im talking about