Physics marathon (hsc) (7 Viewers)

[Danstar2]

Outline the Braggs experiment in determining the crystal structure of material.

The Bragg's used x-ray diffraction to identify the distance between inter atomic planes within a crystalline substance. This was done by directing x-ray rays at a crystal backed by a film. This film gave a diffraction pattern, the Bragg's identified that through constructive interference the x-ray rays would reflect from from parallel planes of atoms. Using the formula n(wavelength) = 2dsin(theta), the Braggs could find d (the interatomic spacing), by using simple right angle trigonometry.

Something like that.

Also @Someth1ng, I said superconductors, (EMS) the German one, uses conventional electromagnets. You only really need to know (EDS) imo. Unless you have to compare them.

 

[someth1ng]

Also @Someth1ng, I said superconductors, (EMS) the German one, uses conventional electromagnets. You only really need to know (EDS) imo. Unless you have to compare them.

What are you talking about? Meissner effect and Maglev trains are two totally different concepts and are unrelated.

 

[barbernator]

What are you talking about? Meissner effect and Maglev trains are two totally different concepts and are unrelated.

No, he is saying that you don't need to talk about EMS in a question that asks about application of superconductors because they don't utilise superconductors, rather conventional electromagnets.

 

[Danstar2]

What are you talking about? Meissner effect and Maglev trains are two totally different concepts and are unrelated.

From Jacaranda textbook "The EDS system, developed in Japan, uses superconducting magnets on the vehicle". Also, "The EMS system, currently used in Germany, uses conventional electromagnets mounted under the train". I never mentioned the Meissner Effect.

 

[RivalryofTroll]

(SGS-05) Explain the importance of Newtons law of Universal Gravitation in understanding and calculating the motion of planets around the sun. (4 marks).

 

[Danstar2]

(SGS-05) Explain the importance of Newtons law of Universal Gravitation in understanding and calculating the motion of planets around the sun. (4 marks).

That's a pretty hard question, but I haven't revised Space yet, I do that tomorrow. I'd say that the gravitational force is inversely proportional to the distance between the planets and the sun, yet we need to also consider the mass of the planets. I'd basically say that using Newtons law of Universal Gravitation we can understand that the gravitational force between planets becomes greater as the mass of the planets increase, or the distance decreases. Not sure, I'm sure someone else knows.

Could probably explain the 'motion' using r^3/t^2 = GM/4(pi^2) let the right side equal a constant. Radius proportional to time... :/

 

[someth1ng]

Oh, yeah. I thought you were referring to my critique of the other response. My bad, sorry.

 

[shongaponga]

lol shonga just realised

the three I was going to say are (spoiler alert highlight below)

g-force = apparent weight/true weight. Apparent weight is the sum of the contact forces acting on a body, and true weight is the normal force on the body when it is stationary on the earth's surface

- Eyes in instead of eyes out approach, and this transverse application of force ensures that blood stays in the brain
- Specially designed suits that support and mold to the astronauts body to ensure minimal stress on body
- Multi stage rocket shutdown to minimise the peak g-force the astronaut is subject to

Hahaha, i read the question wrong

 

[someth1ng]

I would talk about Universal Gravitation giving a possible way of determining the mass of the Sun. The gravitational force between two objects is proportional to the product of their masses and inversely proportional to the square to the distance (inverse square law) between their centres of mass. Refer to F=G... where equating with centripetal force can be used to calculate the mass of the Sun. Without the Law of Universal Gravitation, it would be difficult to predict the force between two masses and so, astronomy would be heavily limited as it would need to rely on significant guesses where the Law of Universal Gravitation could easily explain.

 

[egnaro315]

Maximum EMF occurs when the flux through coil is 0 and the change in flux is a maximum. So when we draw the emf vs time graph for an ac generator do we get a cos graph?

 

[egnaro315]

woops meant emf vs rotation

 

[nirukk]

Explain why the gravitational potential energy of the satellite orbiting Mars is a negative value. (2 marks and only 2 lines given) Any simpler and concise answers ?

 

[Demise]

Explain why the gravitational potential energy of the satellite orbiting Mars is a negative value. (2 marks and only 2 lines given) Any simpler and concise answers ?

The gravitational potential energy is always negative as it is the energy required to move an object from an infinite/very far distance to the point of the gravitational source (0). As it moves closer, the GPE increases to 0, not decreases. - I hope that's concise enough.

 

[J-Wang]

A satellite is to be launched into a geostationary orbit. Given that the Earth's radius is 6.38x10^6m, calculate the height of the satellite above Earth's surface (3m)
Anyone know how to do this?

 

[GoldyOrNugget]

A satellite is to be launched into a geostationary orbit. Given that the Earth's radius is 6.38x10^6m, calculate the height of the satellite above Earth's surface (3m)
Anyone know how to do this?

Kepler's law where T = 24 hours. Solve for r.

 

[Demise]

A satellite is to be launched into a geostationary orbit. Given that the Earth's radius is 6.38x10^6m, calculate the height of the satellite above Earth's surface (3m)
Anyone know how to do this?

Aren't geostationary satellites 36000km above the Earth?

 

[Danstar2]

We'd be looking around 36,000km, so we need approx 3.6x10^7m as our answer. Using r^3/T^2 = GM/4(pi^2)

r^3 = (6.672x10^-11 x 6x10^24)/4(pi^2) x 86400^2)

Then cube root both sides to get r= 4.23x10^7

Take 6.38x10^6m away from the answer and you will get: 3.59x10^7m

For T, I just used 24hours as we know thats the period (hopefully) and you convert it to seconds.

 

[deswa1]

(SGS-05) Explain the importance of Newtons law of Universal Gravitation in understanding and calculating the motion of planets around the sun. (4 marks).

I would talk about Universal Gravitation giving a possible way of determining the mass of the Sun. The gravitational force between two objects is proportional to the product of their masses and inversely proportional to the square to the distance (inverse square law) between their centres of mass. Refer to F=G... where equating with centripetal force can be used to calculate the mass of the Sun. Without the Law of Universal Gravitation, it would be difficult to predict the force between two masses and so, astronomy would be heavily limited as it would need to rely on significant guesses where the Law of Universal Gravitation could easily explain.

Just a general idea of what else I would add- you probs know this but yeah, just in case. You can use Newton's law of gravitation together with centripetal force etc. to calculate orbital velocity (equate the two - use equations) which helps understand the motion of planets around the Sun. Talk about the relation of Newton's law and Kepler's law of periods as well.

A satellite is to be launched into a geostationary orbit. Given that the Earth's radius is 6.38x10^6m, calculate the height of the satellite above Earth's surface (3m)
Anyone know how to do this?

Probs the easiest way to do this is to use the fomula:

r^3/T^2=GM/4pi^2. You know that mass of the Earth (M), you know T (remember to convert to seconds) and then solve for r, remembering to subtract the radius of the Earth from your answer

 

[Keelan134]

gather, process and present secondary information to discuss how shortcomings in available communication technology lead to an increased knowledge of the properties of materials with particular reference to the invention of the transistor

Yeah I dont have any notes on this and HSC online is useless for it.

 

[barbernator]

Here are some more perceptive questions.

a) A satellite was launched from Earth to Mars. What is the optimal point of interception of the satellite with mars' orbit in relation to where it was originally launched from earth to ensure minimal fuel is required for the journey? (2 marks)

b) A satellite is going to use the slingshot effect to gain maximum speed towards a distant star. At what point within the earth's orbit (see diagram) would it be optimal for the spacecraft to use the slingshot effect, and from what direction should it approach and what direction should it leave to maximise speed (assume the spacecraft can approach from anywhere) (3 marks)