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# Tag Archives: Health

## Want to learn fast? Be SMART!

In this busy world everyone wants to save time. Being students, learning is our primary job. To save time, we need to learn faster. But how?

The first step is to have a SMART goal!

S – Specific

M – Measurable

A –  Achievable

R – realistic

T – Time Bound

Having a Specific Measurable Achievable Realistic and Time Bound – SMART goal will increase your efficiency to grasp ideas faster.

While all of you may be having a long term goal, usually what you want to become after studies, you should have a short term goal, an objecting for every sitting of your studies too.

Have a Time Table – be specific what to study and when.

In the time slot for each, decide what and how much to study before you start. Know the outcome expected of you as a result of reading the portion. If it is not mentioned already, it is better to have a look at the questions based on the portion at hand before you actually read the topic.

Learn to read fast. Don’t go word by word while you read. Try to grasp a group of words at a go concentrating on the idea contained. Concentrate fully keeping in mind the objectives/ the questions you read based on the portion.

Do not reread or skip back until you have completed

Practice this daily and try to improve your reading and comprehension skills. This will certainly help you to score more as well as to live well in times to come.

## What is the physical meaning of eigen value?

What is the physical meaning of eigen value? What is the physical meaning of magnetic vector potential?

## Electricity field intensity within a conductor is always zero.Why?

Electricity field intensity within a conductor is always zero.Why?

The main difference between a conductor and an insulator is that the conductors contain plenty of free electrons which are free to move throughout the conductor; whereas the insulators do not have free electrons at room temperature.

When a conductor is held in an electric field, the free electrons inside them instantly drift opposite to the direction of electric field until the electric field due to the drift balances the external electric field and the net electric field inside the conductor becomes zero.

## Does light experience friction?

Does light experience friction?

Asked rashmi (VIII B, KV AFS Bidar)

FRICTION  is defined as the force which opposes relative motion between two surfaces in contact.

If you mean friction in the normal sense as above (as discussed in class), then the answer is “NO“.

Light is a form of energy and not a particle. But it is true that light shows some particle behaviour also.

But, there is a slowing down when light interacts with matter. But, in a homogeneous medium, light has a constant speed. The speed of light is different in different medium.  If we go to the atomic or molecular picture of matter, then we can imagine that light is interacting with a molecule, during the time of interaction, the light can be assumed to have been absorbed by the particle and then it is re-radiated. the re-radiated light travels to the next atom and interacts/absorbed. this slows down the average speed of light, but is constant for a particular homogeneous medium.

The speed of light is maximum in vacuum where there is no matter for light to interact.

So, in between two atoms also, light travels with its branded 3L kmps speed.

Also refer:

1. http://phasing.org/2009/09/25/does-light-have-friction/

## How do we see movies?

We are able to see the movie picture in a cinema hall. Define the phenomenon responsible for it.Explain how does this happen?

The phenomenon responsible here, which enables us to watch the movies and enjoy them is PERSISTENCE OF VISION.

Persistence of vision is the property by virtue of which the image formed on the retina of human eye remains for about 1/15th of a second. So, if more than 15 frames are projected per second on screen one after the other in succession, we wont be seeing them as separate but we will be able to enjoy them as continuous action.

See the following video in which Gagnam Style Video is made out of a series of drawings.

## Buoyancy

A pound coin floating in mercury (Photo credit: Wikipedia)

I read in one of my chapters that when a body is immersed in a container of water (kept on a weighing machine which  reads ‘W’ at first )the apparent weight lost by the body is equal to the buoyant force, and thus the reading ‘W’ increases.

Then I came across a question like this –

A beaker containing water kept on a weighing machine weighs W. A body of weight  ‘w’ is dropped in it. It is floating & experiencing a buoyant force B, then the reading on machine is –

(a)w+W
(b)W+B
(C)W+w-B
(d)W

the book says answer is (a)
but I think it is (c)

(Anwesha posted this questions)

The total force acting downwards is W+w and the weighing scale is providing an equal reaction. the normal reaction offered by the weighing scale is what we get as the reading.

therefore the reading on the weighing scale must be W+w

The buoyant force is acting on the object dropped and is not contributing to the normal reaction offered by the weighing scale.

## Body at incline

1. In first case we have the box with weight, say, 10 Newtons on incline. We calculate two components (perpendicular and parallel)of weight. We calculate normal force and force of friction. The box is at rest.

2. In second case we have ball on incline, made of same material as box from first case. Weight of the ball is the same as in first case, components of weight are the same as in first case. Normal force and friction have the same amount as in the case of box. But,unlike the box, ball is moving – it slides down. How’s that possible? If calculated net force is zero?

It is not true that the ball slides,  but it will roll down.

In the first case, the forces balance each other and there is no motion.

In the second force, the frictional force acting tangentially backwards (up the incline) and the component of weight of the ball acting parallel to the plane and through the centre of the ball constitute a couple and tends to rotate it. Now there is no sliding; it rolls.

(If any further clarification is required please post as comment to this post)

Please refer to http://www.real-world-physics-problems.com/rolling-without-slipping.html for detailed treatment of the Physics of rolling without friction.

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