Physics marathon (hsc) (1 Viewer)

[nucgaek]

Junction between P and N type semiconductors, is subject to high frequency light from the sun. This allows electron-hole flow across the p and n type semiconductors. Holes move to the Positive side, electrons move to the negative side. Electrons are gathered by an outer metal grid which is connected to a circuit and allows current to flow.

Probably need a bit more depth... would that be photoelectric effect?

 

[someth1ng]

Probably need a bit more depth... would that be photoelectric effect?

Yes.

 

[dawooddaman]

Yes.

Brother if Someth1ing tell you to do something you better do that something, or something really bad is going to happen

 

[someth1ng]

Brother if Someth1ing tell you to do something you better do that something, or something really bad is going to happen

Inception shit right there man...LOL

 

[nirukk]

Prediction for an 8/7 marker ?

 

[2xL]

Prediction for an 8/7 marker ?

Will be on motors i think. Hopefully its not space.

 

[tarce94]

Okay so im totally freaking out about tomorrow.

But I have a question its from a trial paper and is worth 5 marks, I was just wondering how people would go about answering it as there isnt much space for writing.

In early studies, the observed characteristics of cathode rays led to the belief that they were electromagnetic waves.
Describe the wave-like properties of cathode rays and explain how other evidence shows them to be particles.

 

[RishBonjour]

Okay so im totally freaking out about tomorrow.

But I have a question its from a trial paper and is worth 5 marks, I was just wondering how people would go about answering it as there isnt much space for writing.

In early studies, the observed characteristics of cathode rays led to the belief that they were electromagnetic waves.
Describe the wave-like properties of cathode rays and explain how other evidence shows them to be particles.

you just regurgitate the wave and particle properties of cathode ray?
e.g. moves a paddle wheel--> momentum-->hence mass--> hence particle (according to early studies)
2 of each would be enough for 5 marks.

 

[someth1ng]

you just regurgitate the wave and particle properties of cathode ray?
e.g. moves a paddle wheel--> momentum-->hence mass--> hence particle (according to early studies)
2 of each would be enough for 5 marks.

I would aim for more than 2 each...

Wave: could pass through metal foil, travelled in straight lines, Hertz invalid experiment showed that it wasn't deflected in electric fields.
Particle: could move a paddle wheel, deflected in both magnetic and electric fields, emitted at right angles from the cathode, velocity far below that of light.

Obviously, I only identified them and you would need more detail in the actual exam.

 

[freeeeee]

Okay so im totally freaking out about tomorrow.

But I have a question its from a trial paper and is worth 5 marks, I was just wondering how people would go about answering it as there isnt much space for writing.

In early studies, the observed characteristics of cathode rays led to the belief that they were electromagnetic waves.
Describe the wave-like properties of cathode rays and explain how other evidence shows them to be particles.

Well firstly you would talk about the limitation of technology (poor vacuum pumps) made experimental data invalid, this is why there were inconsistent results about whether cathode rays were particles or waves.
Secondly you would need to describe at least two experiments for particle (paddle-wheel, electric plate) and explain what the results meant for the nature of CR
Thirdly describe at least two experiment for wave (maltese cross, aluminium foil) and "_____like above____"

thats consistent with the verbs used and should get you 5marks

 

[RishBonjour]

I would aim for more than 2 each...

Wave: could pass through metal foil, travelled in straight lines, Hertz invalid experiment showed that it wasn't deflected in electric fields.
Particle: could move a paddle wheel, deflected in both magnetic and electric fields, emitted at right angles from the cathode, velocity far below that of light.

Obviously, I only identified them and you would need more detail in the actual exam.

But its 5 marks. 1 mark of each property and explaining should get 5 i think :/ Also, note, she said, there isn't much space for writing.

 

[freeeeee]

Question (not a real HSC q) but if someone could explain this to me it would be much appreciated

One of the factors influencing the magnitude of atmospheric drag is the amount of solar wind and radiation, from Jac Txtbook it says solar wind causes the outer-atmosphere to expand, increasing air density so subjecting satellites to more atmospheric drag.

But how does expanding the atmosphere increase density? since D = M/V, if mass stays constant and volume increases shoudlnt density decrease?

 

[tarce94]

Is everyone just doing past papers today for study?

 

[dawooddaman]

Is everyone just doing past papers today for study?

Cramming =(

 

[deswa1]

Is everyone just doing past papers today for study?

I'm lightly going over some theory again and then I'll look at more papers.

Next question: Discuss the advantages and disadvantages of AC and DC motors. (no need to follow write an answer- just dot point it)

 

[barbernator]

I'm lightly going over some theory again and then I'll look at more papers.

Next question: Discuss the advantages and disadvantages of AC and DC motors. (no need to follow write an answer- just dot point it)

DC motor advantages:
- DC motors are used in most household appliances so if DC power transmission was instated, the current would not need to be rectified before being used
- Direct current can be used in superconducting wires with 0 heating loss, so the DC motors can be almost 100% efficient. The continual flux change of AC current causes power loss even in superconducting wires.
- Can have varied rotational speed without using gearing
disadvantages:
- DC motors have split ring commutators which are expensive to manufacture and can be unreliable
- Currently power distribution is AC so rectifiers must be used to provide DC current

AC motors:
- Transformers can only be used for AC current and this makes AC motors easy to use without having to change the direction of current.
- Cheaper to produce
- Less hassles with parts (slip rings do not cause as many problems as split ring commutators)
- Induction motors are easily linked to a three phase AC generator.
disadvantages:
- Synchronous motors must rotate in sync with the AC frequency, 3000 RPM, and to change this gearing must be employed
- Induction motors have considerable power losses and are inefficient

will add more when I think of them

 

[RishBonjour]

for a given power supply, which motor is more powerful, AC or DC and why?

 

[Squishxmishyx]

Advantages of solid state devices vs advantages of thermionic devices.

 

[RishBonjour]

Advantages of solid state devices vs advantages of thermionic devices.

solid state:
- small size--> thermionic devices involve vacuum tubes and are bulky--> limits their use on more complex electrical systems.
- efficient--> thermionic devices have significant heat dissipation thus electrical energy is lost as heat where as solid state devices lose only a fraction of this. Also, thermionic devices require large voltages to run, solid state devices such as transistors, run on much smaller voltages
- No starting time lag---> Thermionic devices need to be heated up first thus slow processing speed
- relatively tough--> solid state devices can endure more physical impact while thermionic devices --> lol--> made of glass and stuff
- Last longer--> thermionic devices have several parts need to be replaced often e.g. the cathode
- cheaper to produce + maintain.



edit:
ohh, advantages of thermionic devices? hmm not sure

 

[barbernator]

solid state:
- small size--> thermionic devices involve vacuum tubes and are bulky--> limits their use on more complex electrical systems.
- efficient--> thermionic devices have significant heat dissipation thus electrical energy is lost as heat where as solid state devices lose only a fraction of this. Also, thermionic devices require large voltages to run, solid state devices such as transistors, run on much smaller voltages
- No starting time lag---> Thermionic devices need to be heated up first thus slow processing speed
- relatively tough--> solid state devices can endure more physical impact while thermionic devices --> lol--> made of glass and stuff
- Last longer--> thermionic devices have several parts need to be replaced often e.g. the cathode
- cheaper to produce + maintain.



edit:
ohh, advantages of thermionic devices? hmm not sure

can create a warmer/more vintage sound than solid state devices which is an advantage for musicians.