 # Lets Study PHYSICS !!!

hello all,i am starting dis thread so that we non engineers,science grads can revise and prepare a bit on physics so that we don’t go blank when questions are showered on us during the interviews… I tried to search alot but couldn’t find any…

hello all,

i am starting dis thread so that we non engineers,science grads can revise and prepare a bit on physics so that we don't go blank when questions are showered on us during the interviews...
I tried to search alot but couldn't find any thread so here goes one...

kindly put all your queries related to physics and science here...and lets together discuss them 😃  a few questions from my side. 1. Optical fibres — how they work?
2. Data and voice transmission — the difference between the two

3. Mobile vs land phones (PSTN). Technology differences.
4. State of Internet in India. What should be done to improve it?
5.
What is Boyle's laws?
6. Kepler's laws and problems to solve
7.
What is Heisenberg's uncertainty principle?  @busar005 said:
a few questions from my side.1. Optical fibres — how they work? 2. Data and voice transmission — the difference between the two3. Mobile vs land phones (PSTN). Technology differences. 4. State of Internet in India. What should be done to improve it?5.What is Boyle's laws? 6. Kepler's laws and problems to solve 7. What is Heisenberg's uncertainty principle?
1. They work using the principle of Total Internal Reflections. TIR is when a ray of light is incident on a refracting surface such that all the energy is reflected back and not transmitted.

5. something to do with the pressure, volume, temperature relations.

6. They state the orbits of planets around the sun are elliptical and the orbits sweep equal areas in equal time. 3rd one can't remember.

7. It states that for any pair of canonical variables, the uncertainty of their product is always greater than or equal to h/2pi . h= Planck's constant. Examples of pairs of canonical variables : momentum and postions ; energy and time

P.S. - I have not googled any of the answers. Otherwise sab complete aur spot on hota. I think we should give it a try without googling it. and later post the correct and complete answers!
What say?

@FingersCrossedd yeah lets try all questions wid out googling nd den we can put correct answers to al the questions at the end of the day 😃 😃
keep posting more questions :)
@busar005 nice start 😃 keep up wid the gud work :)

8. What is Bragg's Law?

9. Briefly explain the principle of relativity
10. Who is your favourite physicist and why?

@sonvi Yeah, lets keep 10 pm as the deadline for each day. and after 10 we'll post the correct answers!

11. What are Newtons Laws ?
12. What is Einstein's contribution in physics ?
@busar005 1) TIR
2) Data Binary , Voice -> analog signal
3) PSTN uses hard lines and wire based, well mobile is mobile 😛 n air wave based
@Brooklyn

Keppler effect bhi padh lo...laws ke allwa wo bhi hoga :P
@FingersCrossedd good suggestion yes,we will try first and then will post answers at the end of the each day..@Brooklyn
@busar005
1 the optical fibres work on the principle of T.I.R(total internal reflection) while the communication through optical fibres is due to intensity modulation of the light rays .

Q3) mobile vs land line: mobiles phones are based on air waves model they have a horn antenna attached to the hand set that sends signals at the specific predefined frequencies. while the land lines uses time division multiplexing techniques and are connected by wires.

Q5) boyles law states that for gases the pressure and volume are inversely proportional provided the temperature is constant.

Q7) uncertainity principle states that its impossible to determine the position as well as speed of a particle. if any of them is determined accurately then the other shall be calculated with an uncertainity of h/4pi.

Q8) braggs law .related to differactions and given by n times wavelength equals to twice the spacing between two planes times sine of angle formed between the incident raay and scattered ray.

Q9) theory of relativity was divided into 2 parts the special theory of relativity and the general thoery of relativity .which proved that speed of light in vacuum is a constant and doesnt depend on the observer .also that time and length can dilate or contract when the bodies or particles are moving with velocitites near to speed of light . the creation of mesons and their reaching the surface of earth is a practicle example.

Q10) fav physicist richard feynman .he always emphasized on the difference between knowing the name of the thing and knowing the thing.

Q11) there are various laws given by newton about motion ,gravitation optics .the classical model of physics is itself caleed the newtonian physics..please be a lil specific .

Q12) classical or newtonian physics failed when the bodies were moving with velocities closer to light . the theory of relativity given by einstein helps us here. the most popular einstein equation energy = mass times velocity of light squared gave the energy mass equivalent.
little less known facts are the prediction of dark matter in the universe by einstein .whihc he could prove that time but now its known to be true . also he tried to give the unified theory .that is one theory that combines everything .which he could not reach to. stephen hawkings is working on the same .

boyle's law i guess suggests that keeping the temperature constant..pressure is inversely proportional to volume

heisenberg's uncertainity principle suggests dat the position nd speed of a perticel cannot be given at the same tym...

Kepler's law are opticals are elliptical in shape,line joining planet nd sun sweeps equal area in equal time and the square of the time taken to complete one revolution is directly propostional to cube of semi major axis of ellipse

principal of relativity E=mc^2

newton's law
1. everybody continues to be in its state unless an external force is applied on it.
2. rate of change of momentum is directly proportional to force applied..
3. to every action,there is an equal and opposite reaction.

my favourite physicist is einstein--..he has contributed not only to physics but to chemistry and maths also...nd his greatest contribution to physics was his theory of relativity...dats d base of our science,if dis theory fails whole science will change..

questions :P

13.What is Boyle's Law?
14.What is Archimedes Principle?
15.What is the difference between mass and weight?
16.What is specific gravity?
17.What is the Plimsoll Line?
18.What is surface tension? Give some examples.

OA FOR SET 1

1. optical fibres work on the principle of total internal reflection.

2 and 3. earchunifiedcommunications.techtarget.com/feature/Learning-Guide-How-is-transmitting-voice-different-from-sending-data

5. boye's law-keeping temperature constant, pressure is inversely proportional to volume i.e.

PV = CONSTANT

6.Kepler's three laws of planetary motion can be described as follows:
(I) The path of the planets about the sun is elliptical in shape, with the center of the sun being located at one focus. (The Law of Ellipses)

(II) An imaginary line drawn from the center of the sun to the center of the planet will sweep out equal areas in equal intervals of time. (The Law of Equal Areas)

(III) The ratio of the squares of the periods of any two planets is equal to the ratio of the cubes of their average distances from the sun. (The Law of Harmonies)

7.HEISENBERG UNCERTAINTY PRINCIPLE- the position and the momentum of a particle can't be measured simultaneously with arbitrarily precision. The more precisely the position is determined, the less precisely its momentum can be known at the same instant.  @sonvi said:
questions13.What is Boyle's Law?14.What is Archimedes Principle?15.What is the difference between mass and weight?16.What is specific gravity?17.What is the Plimsoll Line?18.What is surface tension? Give some examples.
13. It states that on a constant Temperature, Pressure in a confined system due to a particular gas is inversely proportional to its Volume!!
P = k* (1/v)
=> PV = k ; k = constant

It is also extended for non-constant temperature conditions as- PV/T = k

14. It states that the Upward force (Buoyant force) that acts on the body in a liquid is equal to the Weight of the Liquid displaced by you!! i.e. Fully/ partially Immerse an object in a filled-up-to-the-brim bucket... Now, if you collect the water overflown/displaced from bucket and weigh it.. it would be equal to the immersed object's weight!!

15. Mass is actually the measure of matter we are made up of, whereas Weight is the Force acting on the body due to gravity.
i.e. if your Mass = m = 20 kg
then your Weight = Force due to gravity = mg = 20*9.8 = 196 Newtons
where, g = acceleration due to gravity = 9.8 m/sec^2
Though, we often refer mass as weight in our layman language, which isn't right! :P

16. Specific gravity is the Density of an object with respect to some reference object.

S.G. = (Density of a Substance)/(Density of some reference substance, mostly Water) = Ds/Dw
=> Weights/Weightw (when, volume is same)
Since, Density= Weight/Volume
Mainly used in Fluids and Gases, Water is mostly taken as a reference substance.

17. Don't know. Where did you get this from?? :P

18. Surface Tension is the property of the 'Surface' of a liquid to resist the external forces. It is due to cohesion among molecules of similar nature that keeps it intact.
It is also the reason for the spherical shape of Water drops. Due to surface tension, the surface tends to be in the least area formation. Another example can be the Bubble formation in Water.

P.S. I need to revise my notes!! 5 years since I read them!! I may not be fully correct at some places!! @hanushanand yeah go ahead nd revise...i need al of ur's help to work on it now 😃 :)
and i will post the answers soon ... will tag you then :)

Ques : : mention the failures of third law of newton.

19. What is the difference between centripetal acceleration and centrifugal force?
20. What is the conventional direction of flow of current in a metallic conductor ?
21. Can you measure e.m.f. of a cell with a voltmeter ?
22. Which one is greater -e.m.f. or terminal p.d. across the cell ?
23. Two solid pieces one of gold and the other of silver weigh the same in water. which will weigh more in air ?
24. Why the brake drums of a car are heated, when it moves down a hill at constant speed ?

Q)if a tunnel is dug from North Pole to South Pole and a stone is dropped into it,what would happen to the stone?