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[obimoshman1234]

Heat: The considerable kinetic and potential energy possessed by an orbiting spacecraft must be lost during re-entry. As the atmosphere decelerates the spacecraft, the energy is converted into a great deal of heat. This heat must be tolerated and/or minimised. The heat can be tolerated by using heat shields that use ablating surfaces (as used on Apollo capsules) or insulating surfaces (as used on the space shuttle). The heat can be minimised by taking longer to re-enter, thereby lengthening the time over which the energy is converted to heat. The space shuttle uses this technique. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o></o>
g forces: The deceleration of a re-entering spacecraft also produces g forces, typically greater than those experienced during launch. High g forces can be better tolerated by reclining the astronaut, so that blood is not forced away from the brain, and by fully supporting the body. The g forces can be minimised by extending the re-entry, slowing the rate of descent. This strategy is employed by the space shuttle.


ok my uestion:
The Hertz experiment was thought, in 1888, to have provided the final experimental evidence of the nature of light. Discuss the methods employed by Hertz in the experiment and the model of light that his experimental results clearly supported 7marks

 

[sonnylongbottom]

The Hertz experiment was thought, in 1888, to have provided the final experimental evidence of the nature of light. Discuss the methods employed by Hertz in the experiment and the model of light that his experimental results clearly supported 7marks

Hertz used an induction coil to generate a spark. What he observed in a transmitter with a gap, was that another spark jumped across the gap. This spark was generated from the electromagnetic radiation from the induction coil. This was known as the photoelectric effect. He showed these waves behaved just like light waves as they could be reflected, refracted, polarised and diffracted. Hertz used a determined frequency in an oscillating circuit and a known wavelength, he determind the velocity of the waves. By comparing it to Maxwell's equations v=f/(, these waves corresponded to the speed of light 3 x 10^8 m/s.

Outline the discovery of electromagnetic induction by Faraday and evaluate implications of his discovery

 

[a1i2d3e4n5]

Outline the discovery of electromagnetic induction by Faraday and evaluate implications of his discovery

Michael Faraday predicted that if a force could be made in a current carrying conductor via a magnetic field then by applying a force to a conductor which is inside a field then a current will be produced. Faraday Moved a conductor relative to a magnetic field and observed this.
(not sure about implications but ill give it a shot anyways)
Faraday made conclusions about the implications of his discovery:
Strength of Magnet
relative velocity between magnet and conductor
angle of relative motion
length of conductor within the Field

Describe the term "back emf" and account for Lenz's law in terms of conservation of energy and relate it to the production of back emf in motors.

 

[aussiechick007]

Outline the discovery of electromagnetic induction by Faraday and evaluate implications of his discovery

Michael Faraday discovered that by moving a magnetic field relative to a conductor, so that the conductor is cutting a magnetic flux, a current can be induced in the conductor. This discovery formed the basis of the modern generator, allowing electricity to be produced simply. Before this time, electricity had to be produced by galvanic cells, in which the current produced decreases over time. With Faraday's discovery which formed the basis of the generator, there was now a more reliable source of electricity. This was a good thing because now electricity was readily accessible.

How does Einstein's Theory of Special Relativity explain the result of the Michelson-Morley experiment? (4 marks)

 

[sonnylongbottom]

How does Einstein's Theory of Special Relativity explain the result of the Michelson-Morley experiment? (4 marks

Einstein's theory of Special Relativity states that the speed of light is constant irrespective of the frame of reference. The Michelson Morley experiment aimed to detect the presence of the aether (the medium which light travels through). By projecting a beam of light at a half silvered mirror, the light ray split, forming two rays, one perpendicular to the other and in phase with one another. By rays hit mirrors which are equidistant and then reach an inferometer where a pattern was recorded. The experiment was rotated 90 degrees and repeated as a new pattern was expected from the light travelling relative to the aether at a different velocity. However no new pattern was recorded, determining the null result and proving the speed of light is constant regardless of what frame of reference it travels through.

Describe the main features of an AC motor and their operation

 

[Graceofgod]

How does Einstein's Theory of Special Relativity explain the result of the Michelson-Morley experiment? (4 marks

Einstein's theory of Special Relativity states that the speed of light is constant irrespective of the frame of reference. The Michelson Morley experiment aimed to detect the presence of the aether (the medium which light travels through). By projecting a beam of light at a half silvered mirror, the light ray split, forming two rays, one perpendicular to the other and in phase with one another. By rays hit mirrors which are equidistant and then reach an inferometer where a pattern was recorded. The experiment was rotated 90 degrees and repeated as a new pattern was expected from the light travelling relative to the aether at a different velocity. However no new pattern was recorded, determining the null result and proving the speed of light is constant regardless of what frame of reference it travels through.

Describe the main features of an AC motor and their operation

That barely answers the question imho.

 

[sonnylongbottom]

ok what did i need

 

[old.skool.kid]

How does Einstein's Theory of Special Relativity explain the result of the Michelson-Morley experiment? (4 marks

Einstein's theory of Special Relativity states that the speed of light is constant irrespective of the frame of reference. The Michelson Morley experiment aimed to detect the presence of the aether (the medium which light travels through). By projecting a beam of light at a half silvered mirror, the light ray split, forming two rays, one perpendicular to the other and in phase with one another. By rays hit mirrors which are equidistant and then reach an inferometer where a pattern was recorded. The experiment was rotated 90 degrees and repeated as a new pattern was expected from the light travelling relative to the aether at a different velocity. However no new pattern was recorded, determining the null result and proving the speed of light is constant regardless of what frame of reference it travels through.

Describe the main features of an AC motor and their operation

Induction AC motor:
Stator- is a powered, radial AC electromagnetic coil.
Rotor- is a "squirrels cage" which is not electrically connected to the stator or any power supply. The huge advantage of the induction motor is that it has no connutator. As the external magnetic feild of the stator changes due to the AC supply, it causes a flux change in the squirrles cage. this induces an emf which induces a current in the mrotor bars. These induced current experience the motor effect and causes a torque which turns the rotor at the same rate as the changing B field.

Also universal motor but cbf.

Next: In a cathode ray tube an electron gains a velocity of .6c. The distance between the anode and the screen, as measured in the electrons frame of reference, is 0.24m.

Calculate this distance as measured in the labaratory frame of reference.

 

[alez]

l=lrt(1-v^2/c^2)
.24=lrt(1-.6^2)
.24=.8l
l=.3m

 

[aussiechick007]

Next: In a cathode ray tube an electron gains a velocity of .6c. The distance between the anode and the screen, as measured in the electrons frame of reference, is 0.24m.

Calculate this distance as measured in the labaratory frame of reference.

0.24 = lo (1-0.6^2)^0.5
lo = 0.3 metres

Some materials become superconductors when cooled to extremely low temperatures. Identify THREE properties of superconductors.

 

[old.skool.kid]

Okay so you guys were right, but i got that question wrong when i did it. I always get confused, how do you guys work out which ones are lo and lv?

 

[alez]

the electron is moving close to c, so from its p.o.v length will contract
the observer would see the object that is moving contracting in length, not where it is travelling (eg in the q, the electron would be seen to contract, not the crt)

 

[alez]

Some materials become superconductors when cooled to extremely low temperatures. Identify THREE properties of superconductors

Below critical temp, no resistance
Exclude magnetic field lines
Can carry large currents with no heat (but i think this is just an expansion on the first one and not really a point)

Explain how the addition of trace amounts of certain elements can change the electrical resistance of semiconductors at a given temp

 

[Graceofgod]

ok what did i need

More about einstein, don't really explain the connection.

 

[old.skool.kid]

Ok thanks i think i get it..

Intrinsic semiconductors have too little conductivity to be useful in circuits. Their conductivity can be increased by adding impuritites.
P-type semiconductors use a group 3 element such as alluminium, as these only have three valence electrons, allowing the fourth bonding position to become a positive hole. positive holes move in the direction of the aplied voltage.
N-type semiconductors use a group 5 element such as phosphorus as these have 5 valence electrons, with one electron becoming relativly free for conduction. The free electrons move in against the applied voltage.
The doping of semiconductors using these elements significantly decreases their electrical resistance.

Next:Explain how an understanding of black body radiation changed the direction of scientific thinking in the early 20th century.

 

[dwarven]

0.24 = lo (1-0.6^2)^0.5
lo = 0.3 metres

Some materials become superconductors when cooled to extremely low temperatures. Identify THREE properties of superconductors.

0 resistance.
diamagnetic
something else

 

[dolbinau]

Could we just say electrons travel in pairs (Cooper pairs), separate to 0 resistance? That's three, lol.

 

[Pwnage101]

hey guys, can someone help me with something thats buggiong me - what was 'the contribution of einstein to quanum theory and its relation to black body radiation'?

i can explain how einstein explained the photoelectric effect, but i cant explain how he helped explain BB Radiation - i though that was all planck????

help much appreciated!!!

 

[helper]

0 resistance.
diamagnetic
something else

SAy analgous to diamagnetic because it isn't diamagnetic. Meissner effect would be a better way if identifying that.

OTher things, can't remember what others have posted.

Critical Temperature
Critical MAgnetic Field Strength

 

[helper]

hey guys, can someone help me with something thats buggiong me - what was 'the contribution of einstein to quanum theory and its relation to black body radiation'?

i can explain how einstein explained the photoelectric effect, but i cant explain how he helped explain BB Radiation - i though that was all planck????

help much appreciated!!!

Link is that he took Plank's idea and applied it to light. This meant it wasn't a property of the blackbody producing quantised eneergy amounts but it was a property of the energy that meant it had to be emitted in quanta. He gave a physical meaning to the quanta being emitted by the black body.