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# Monthly Archives: June 2011

## What is an electron made up of?

We have all studied that electrons are among the constituents of an atom. But are they made up of still smaller bits of matter? This question was asked by Ela.

“charge is a property possessed by matter, then waht electron actually is?”

Before giving my answer to this question, I will wait for response from the members and visitors at askphysics.com

(Please try to be logically sound and avoid grammatical errors when you post your answers as email or comments to this post. Visitors from other countries (non English) can use the Google translate facility to read the post in their language and translate the response from their language to English before posting comment or sending email.)

## Problem from Force and Laws of motion

Can you solve this:

“A pole vaulter crossing the bar kinds on a foam cushion this downward speed as he first touches the cushion is 6.8 m/s,and he sinks 25cm , into the cushion before stopping. Estimate his acceleration while being stopped by the cushion”

This Question was posted by mimi mendoza

## Can a body be said to be at rest as well as in motion at the same time?

“Can a body be said to be at rest as well as in motion at the same time?”

This question was asked by Anmol.

Motion and rest are relative concepts. There is no absolute rest. We can define the state of rest or motion only with respect to another object or a point in space taken as reference.

For example, a person inside a train considers himself to be at rest with respect to the fellow passengers or the walls of the train. But when he looks outside, he finds himself to be in motion with respect to the trees outside.

Hope the idea is clear.

## How does dielectric constant depend on nature of medium?

How does dielectric constant depend on nature of medium?
Does this have any relation with free electrons and force between molecules?

Dielectric Constant, also called relative permitivity of a medium depends on the electric susceptibility of it, the ease with electric flux lines can pass through it.

The susceptibility depend on molecular polarization, the electric dipole moment acquired per unit volume in an external electric field.

So, the thing to note is that, dielectric constant is a physical quantity measured as a comparison of the strength of electric field in vacuum to that inside the material.

Dielectric constant can be defined in terms of electrostatic force

$K=\frac{F_{0}}{F_{m}}$

Dielectric Constant can also be defined in terms of capacitance.

$K=\frac{C_{m}}{C_{0}}$

1. In the chapter electrostatics,we studied about electric flux. there area vector is considered and my teacher told that it is perpendicular to the surface. but i didn’t get what does it mean yet now.would you please mind helping me to knw abt it? can you define it in simplr words?
2. why gausian surface is to be considered??
3. we know force is a vector quantity. so it should be added by using vector addition methods. but by superposition principle, we just add two/more forces. how can we relate these??
4. intensity of electric field is defined as the force experienced by unit possitive charge at that point. we know
E=F/q = k.q/r2. but in the case of only one charge placed at a point, how r is to be considered? is there any electric field intensity?
5. speed of light is cosmic speed limit.why?
6. what is the frequency of sound produced by a aluminium string
7. I want to know about the pointed conductors on the top of the building that r used to send the thunders into the ground. The area that the pointed conductors cover ,is it possible to  send the thunders into the ground on the large buildings of huge area.
8. name of two materials used for making resistance wire
9. we have theory in atomic structure that mass of electron in motion deffers fron at being rest and it will be equal to infinitive if it travel with the speed of light , if it is really applicable to all the masive particles , mass of photon wouldalso be equal to infinite and as it travells with the speed of light,then it would form a black hole entire world will be a black hole then ,what is your explaination to this?
10. I watch a lot of Rugby League, and there is a rule that the ball must be thrown either backwards, or sideways, but never forwards.
My question is this: If a player is running forward and passes the ball exactly sideways (perpendicular to the running direction), will the ball travel forwards relative to the ground or will the momentum of the player be transferred to the ball?
11. a metre scale is caliberated @degree celsius to give correct reading.Find the distance between 50 cm and 51 cm if the scale is used @10 degree celsius.coefficient of linear expansion of steel is 1.1*10-5.
answers given in two books are 1.00011cm and 0.99988. why this contradiction?
12. Can mass be a negative? if yes plz explain me…
13. set up the schordingers time independent equation for a linear harmonic oscillator?
14. we have partially designed a transmission system with the help of springs which in function would be able to replicate gears but we are unable to understand the mechanics of the system for prediction. It was just a idea that we decided to try out and on our trials the system seems to work but is chaotic can you help us with the mathematics of it.
15. What is the reason for gravity ?
16. Why the light is transmitted by a polarizing sheet is always polarized parallel to the polarizing direction of sheet ?
17. Light of wavelength 450 nm is incident normally on a grating with 300 lines per millimeter. How many orders of diffraction maxima can be obtained?
18. why water has more dielectric constant  than mica. please explain.
19. A ball suspended by a thread swings in a vertical plane so that its accleration values in the extreme and lowest position are equal.Find the thread deflection angle in the extreme position?
20. A body of mass 5kg is taken on equitorial plane. But due to some change earth’s diurnal motion, its weight has become zero. What will be the length of day now?
21. Over the course of about six weeks in 1992, Aki Matusushima, from Japan, rode a unicycle more than 3000 mi across the United States. Suppose Matsushima is riding through a city. If he travels 250.0 m east oone street, then turns counterclockwise through a 120 degree angle and proceed 125.0 m northwest along a diagonal street, what is his net displacement?
22. when the distance between the sun and the earth is halved how many days would be there in one year of earth?
23. can mass of a charged particle be infinite and if yes explain how and when?????
24. What is the physical interpretation of the imaginary part of schrodinger’s wave functions?
25. why our eyes cannot give chromatic aberration? and why is it that way?
26. why bicycle wheels are fitted with spokes?
27. When an oscillator circulates constantly with a stable periodicity (by positive feedback loop) can it evolve (in its periodicity)  the other oscillators which periodicities circulate by negative feedback loops?
28. How we understand ic chips?
29. How magnetic field and electric field support to each other in the propagation of E.M waves?
30. Two winches on a wharf, attached by cables (say 100m long)to a floating buoy (say 100m distance D from the wharf), pulling on the buoy at the same constant rate (say 10m of cable wound in per sec). If the winches are side-by-side (Separation S=0m)then there is no accelleration of the buoy, just a constant 10m/sec velocity (V) and the buoy takes 10 secs to reach the wharf (D=0). If however, the winches are 10m apart to start with (S=10m), then the buoy accellerates as it gets closer to the wharf (as D decreases). If the winches are 20m apart then the accelleration is even greater than at 10m apart! I would really like to know what the relationship is(equation)between the separation of the winches (S), the distance of the buoy from the wharf (D)and the change in velocity of the buoy (V). It appears to be an inverse exponential relationship between V increasing and D decreasing, and the relationship is directly proportional to the separation S. I have used Pythagoras’s Theorm (D-squared + S/2-squared = L-squared)to calculate the change in speed of the buoy, for differing separations of the winches. The further apart the winches are, the closer the buoy is to the wharf to start with. Hope this makes sense.

## A Quantum Physics based Question : Can Anyone answer this?

Can anyone answer this Quantum Physics Based question posted by Ian Mc Tavish?

“I would very much like someone who has access to the necessary equipment to perform the following suggested experiment or let me know if this has already been done and what the results were.

I should apologise in advance for my lack of proper scientific terminology as I have had no formal physics training other than the thought experiments I have posed to myself and reading a few books on physics and astronomy and articles online.

Firstly, I understand that when light is shone through two slits it causes a pattern of light and dark on the screen behind thus suggesting that light is a wave.

Secondly,  when the rate at which the light is emitted is slowed down so it can only be a photon(?) at a time there is still an interference pattern.  Suggesting the photon goes through both slits at the same time and somehow interferes with itself….giving birth to quantum physics and a whole lot of outlandish theories (I have an even more “outlandish” theory myself)

Finally, it gets even stranger, when any kind of device is put in place to measure or count which slit each light particle is going through, the pattern changes to diffuse. At last being what you would expect to see from individual particles.

The strange part is, of course is how can just the act of observing cause a diffuse pattern. If the measuring device is switched off it goes back to bands of light and dark.

I hope I have this reasonably correct so far ?

SO…..what would happen if the device that measured which slit photons went through was powered by some kind of voltaic cell that was placed where the light bands are.

That is to say only when the light was making the banded pattern would the power be sufficient to switch on the device measuring which slit the light particles went through….which will then make the pattern diffuse….which will switch off the machine…….which will then make the pattern banded……which will switch on the machine…..ad infinitum.

This seems to cause the same paradox as Schroedinger’s Cat but a lot easier to test and more animal friendly…..a bit of Hawkins style humour there…haha.

If this is the first time someone has suggested this and it does prove useful in any way I would very much like to make my parents proud and have this referred to as the “McTavish Twist”.   The first part being my surname and “twist” because I love twists in both science and cocktails !!!  Both are refreshing and alleviate the boredom..

One suggested result is that the measuring device switches on and off at the speed of its slowest component.  If there was nothing slowing down its rate of switching then it would be very interesting to measure the number of times it changes state per second ?  Although I imagine this may take some clever machinery indeed as the resulting figure should be the smallest possible measure of time.  A “universal tick” ?  (maybe we can call it a “McTavish Tick” or am I getting greedy !!).  I imagine this should link mathematically to the maximum speed of light in some way.

Another possible outcome is that the machine will not switch on even though the light level appears sufficient to power it.  This could happen because it is only really at half power…..being half in the diffuse pattern (that is to say half in another state/universe).  It may be interesting to note where the “tipping point” is ?  Does it really work out to be exactly one half or does it lean more towards one state ?  Again this ratio may link mathematically to another well known number.

I imagine the actual results of the experiment will lead as usual to more questions.  I would very much like confirmation of the results so my own thought experiments move on to new questions too.

Thank you sincerely for your attention.”

Experts in the field are requested to respond

## Free electrons in Materials and shock?!

Sachin asks: “Sir I am not able to understand that conductors n insulators have free electron n moving randomly in direction but the definition says that FLOW OF CHARGE PER UNIT TIME IS CALLED CURRENT. SO my question is electrons are moving in both conductors or insulators but when touch them they don’t produce electric current why ???”

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