WHY THE WAVES CAN BE FOCUSSED?

We see parabolic antenna everywhere, in mobile towers, in TV reception at home. Parabolic mirrors are the main component in space telescope. Let us see why they bring rays or waves to focus.

In the above figure, the light rays are reflected by the parabolic mirror and meet at the point F called focus. Light rays are reflected according to the law of reflection. The law of reflection works based on the principle that a wave always takes the path of least time.

In the same figure, below the horizontal line, all the rays travel equal distance before meeting at the focus F (1). Also all the rays take equal and least time (2). Only one point F satisfies the above two conditions for all the rays. Hence all the rays ultimately meet at the focus. This is the principle for all the focusing devices and also for all the waves likes electromagnetic waves, heat waves, sound waves and light waves.

Let us see another interesting example of focusing. Take an ellipse

Ellipse has two focus (rightly named). Take any point on the ellipse. Find the distance between the point and one focus. Also find the distance between the point and another focus. Add the two distances.
Repeat this calculation for many points on the ellipse. You can find that the total distance is same and constant for all the points on the ellipse.

Suppose you keep a source of light on one focus. The rays get reflected by the wall of ellipse and coverage on the second focus. It is because, the two conditions are satisfied here also. That is, the distance traveled by all the rays are the same as explained already and all the rays take least and equal time to reach the second focus. This property of the ellipse is used in hospital to focus shock waves and break kidney stones.

If a set of parallel light rays pass through a glass lens, they get focused on the other side of the lens. Here the rays travel in air and glass. Lens is a curved one and has a varying thickness. Hence the rays travel different distances inside the lens. Also the rays bend at different angles and take different inclined paths. But all the rays take the same and least time to reach the focus. In the case of lens, the distances traveled are not equal but the time taken is equal.

We can define a 'focusing device' as an object which facilitate the light rays to take the least and equal time to reach a point'. Using the above principle, one can experiment to find substitute for the glass lens which has been ruling the optical world for a long time. "Fresnel lens" is a step in this direction-explore.

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THE EARTH, A SUPER ORGANISM

JOIN MY COURSE: "Become a programmer in a day with python" A man called 'love lock' (what a name) proposed a theory called Gaia theory, named after Greek Goddess. It says, "Earth is a self-regulating organism like a human being. The organic life in it interacts with in-organic matter and maintains atmosphere, temperature and environment". Hence the earth is still suitable for the life to thrive. Imagine, in a particular place, there are lot of flowers. Some flowers are white and some are darkly coloured. We know, white reflects light and heat while dark absorbs the same. White flowers can thrive in hot climate. But dark flowers requires cold climate. The absorption and reflection balances and the environment reaches average, warm temperature at which both the flowers can co-exist. This is the essence of "Gaia" theory. On our earth, the oxygen constitute 20% of the atmosphere. The oxygen level is always mai

THE PARABOLA

A jet of water shooting from a hose pipe will follow a parabolic path. What is the so special about parabola. Y= x^2 Draw a graph for the above equation. It will result in a parabola. This parabola is also called unit parabola. Any equation involving square will yield a parabola. Example: Y = 2x^2 +3x+3 (also called quadratic equation) X= 2 and -2, both satisfies the equation 4 = X^2. Parabolic equations always have two solutions. Any motion taking place freely under gravity follows parabolic path. Examples: An object dropped from a moving train, A bomb dropped from flying plane, A ball kicked upwards. If a beam of light rays fall on the parabolic shaped mirror, they will be reflected and brought to focus on a point. This fact is made use of in Dish Antenna, Telescope mirrors, etc. Inverted parabola shape is used in the construction of buildings and bridges. Because the shape is able to bear more weight. A plane

DISORDER IS THE "ORDER OF THE DAY"

Imagine a balloon full of air. The air molecules are moving randomly inside the balloon. Let us pierce the balloon with a pin. The air rushes out. Why should not the air molecules stay inside the balloon safely and ignore the little hole? That is not the way the world works. The molecules always "want to occupy as many states as possible". Hence the air goes out in the open to occupy more volume. The things always goes into disorder (entropy) and the disorder increases with time. The above statement is what we call "second law of thermodynamics". Consider a cup of coffee on the table. Suppose the heat from entire room flows to your cup of coffee, the coffee will boil and the rest of the room will freeze. Freezing means bringing things to order and arrangement. It violates the second law. Hence it will never happen. Hence heat must flow from high temperature to low temperature and not the other way. The air molecules in y

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