A Face Book conversation on relativity and its effects

Relativity has fascinated many young minds (old too).

Below is a conversation between a student and a Physics Teacher on Facebook chat.


hlo sir,

did u watch interstellar movie??

kk… i hv a doubt regarding g concept??

c according to relativity-a person hu went to space wud xperience time dilation compared to us on earth…. then it’s also possible tht. gravity here on earth is more than away from earth,i.e.gravity curves spacetime,thus dilatin time here on earth compared to a spacecraft man…..these two concets are contradictory???
its not away from gravity that causes the time dilation, but the speed of motion
the relativistic effects are prominent only when the speed of motion reaches the speed of light
or nears the speed of light
every derivation in relativity is based on the speed of light
according to rel, the speed of light is the only entity which can be taken as not changing
or absolute
all other physical quantity is relative

kk….bt wht causes time to go slower near a black hole???
acc to relativity, it’s the increased speed
just like a stone increases its speed while nearing the earth when falling from a ht

gravity is incorporated into sp theory of rel…

and this causes curving of space time???
Gravity causes curvature in the space time continuum
this explains why two masses attract each other

ya bt still i dnt get ???
read it

c a person spending time near the event horizon,time slows down compared to a person in a space craft moving at a considerable speed???this can similarly apply to earths frame instead of event horizon???
A person spending time at event horizon cannot be at rest
Please read more and think

kk…i shall surely read that.,bt i hv a plus2 physics doubt too??

the speed of an em wave is the sp of light..,bt em wave composed of electric and magnetic fields is related to charges.,hw cum these charges move at sp of light???doubt frm ncert txt on velocity selector

qe=qvb and v=e/b
4 minutes ago
charges are not moving in an em wave
it is the time varying electric and magnetic fields which are propagating.
the fields are produced by accelerated or oscillating charges
but the charges are not moving along with em waves.
an em wave does not possess any charge

New light to illuminate the world – the inventors of LED gets Nobel Prize 2014

According to the official press release,
The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Physics for 2014 to

Isamu Akasaki


Meijo University, Nagoya, Japan and Nagoya University, Japan

Hiroshi Amano
Nagoya University, Japan


Shuji Nakamura
University of California, Santa Barbara, CA, USA

“for the invention of efficient blue light-emitting diodes which has enabled bright and energy-saving white light sources”

Continue reading…


Numericals from Newton’s Laws of motion based on F=ma (For calss XI students of Kendriya Vidyalaya Pattom)

Download the questions and solve them and submit on or before 9 Oct 2014

  1. A force acts for 10 s on a body of mass 10 kg after which the force ceases and the body describes 50 m in the next 5 s. Find the magnitude of the force. [Ans: 10 N]
  2. A  truck starts from rest and rolls down a hill with constant acceleration. It travels a distance od 400 m in 20s. Calculate the acceleration and the force acting on it if its mass is 7 metric tonnes. [Ans: 2 m/s2, 14000N]
  3. A motor car running aat the rate of 7 m/s can be stopped by applying brakes in 10 m. Show that total resistance to the motion, when the brakes are on is one fourth of the weight of the car.
  4. In an Xray machine, an electron is subjected top a force of 10-23 N. In how much time the electron will cover a distance of 0.1 m,? Take the mass of the electron = 10-30 kg