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Relativity, Black Hole and some doubts

In the model of the big bang I would like to pose the following question. My understanding is that

1. The expansion of the universe is accelerating and

2. The radiation or shock wave to keep the analogy going is something we can measure.

My question is this. While we can rewind the clock to a single moment when the universe was infinity dense how do we know that this was a moment at all. Let me elaborate. As the universe expands could time or space time not also expand and if so than when the big bang occurred is something we cannot measure merely by rewinding the clock. If we are experiencing time at a given rate when the universe is at its current size would time not be being effected by the expansion also and if so would that mean the there was simply no start and no end to the universe? Perhaps the big bang is not as accurate as we may wish and perhaps it is our ability to comprehend that is limited. I propose there is no start or end to the universe it has always and will always be as it, and we, cannot exist without time and as such these two objects or things form a symbiotic relationship with each other. While the universe expands so does time and its effects are reduced in line with its expansion. Does this sound plausible and if not why?

Radiations sensed by eyes

Arun Asked:
“What form of radiation can your eyes detect? sir, please answer this question”
Normal Human Eyes can sense the visible spectrum only.

“The visible spectrum is the portion of the electromagnetic spectrum that is visibleto (can be detected by) the human eye. Electromagnetic radiation in this range ofwavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm.[1] In terms of frequency, this corresponds to a band in the vicinity of 400–790 THz.” ———– Wikipedia

Question on distance, acceleration and velocity

Two cars start simultaneously form rest at the same place. one accelerate uniformly as 0.5m/s until it reaches a speed of 60m/s which it maintains steadily, the other accelarate uniformly at the speed of 80m/s which it maintained steadily. calculate

1. How many seconds will elapse before the cars are levelled and each travelling at equal speed.

2. the distance travelled by either car this time.

Electricfield, Magnetic Field and Photon

We know that photon has no charge. Then where from it gets electric and magnetic field in light?

Malik Sajad asks


Electric and magnetic fields are not produced by the photon; it is massless too.

But, photon is created by time varying electric and magnetic fields, usually produced by accelerated charges.

As you might have already learnt, a charge at rest produces an electric field around it. A moving charge (current) produces a magnetic field around it as well as magnetic field. A varying current produces a varying magnetic field and hence an induce emf or current. An accelerated charge produces a time varying electric and magnetic fields.

Thus under suitable situations, the electric and magnetic fields can reinforce each other and propagate out as pure electromagnetic form of energy and such a packet of energy is called photon.

Solving problems on Laws of Motion

Sir,in solving problems of laws of motion ,is it mandatory to take that direction as +ve in which acceleration acts?(i.e should i subtract other forces acting on a body from the forces that is acting towards the acceleration)


(Pranay Talukdar asks)

Answer: In general, we take the forces in the direction of acceleration (I.E, ENHANCING THE ACCELERATION) and the forces against the acceleration as negative.

The first step in solving such problems is to draw a free body diagram and represent all active forces and reactions to constraints in vector form with proper direction ad label. This will highly simplify the problem.

Science model on energy transformations

I have got an assignment from school about making an energy transformation model and I have no idea what to do!
Can you help me? (Posted by Maddy on 28 Aug 2011)

(Expecting suggestions from visitors and members)


There are many simple models for energy transformation. One of the themes for this years Science Exhibitions suggested by NCERT is “Energy Conservation”.

Any generator is a device for energy transformation.

You can think of any device which can convert energy from one form to another.

How does light travel?

Akashjot Kaur asks

“how a wave travels ? eg. light has dual nature ,since  light consists of particles ,and in the wave character we say it moves in the form of electric & magnetic perpendicular wave.how is it possible? it travels in the form of waves or particles?”

Answer to be posted soon

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