Monthly Archives: March 2003

SUPERHEATED WATER

 

      To understand this phenomenon we would have to understand how water boils in ordinary pans on the stove. When you heat water in a pan over a stove its temperature slowly rises.

At near its boiling point small bubbles start forming in little cracks in the base of the pan. Now all pans contain certain imperfections. These imperfections contain some air. This air escapes at about 30 degrees less than the boiling point.

At about the boiling point these imperfections become the place where water vapour bubbles form, rise up and escape into the air. These bubbles carry away excess heat.

      When you heat water in a glass or a smoother surface these are less chances of imperfections and bubbles take longer to form.

      So these imperfections act as seeds around which state change first occurs. THis is similar to the condensation. Condensation usually starts around some seeds. This is why sometimes clouds are seeded to enable rain.

      Now what happens when you heat water in a microwave? Usually you use ceramic bowls and these are pretty smooth. The water is heated from all sides. IN the pan over stove the water is heated from the bottom which is near a surface. In a microwave water is heated evenly. The water on the surface or in the middle does not touch any surface and any imperfection. So sometimes water may heat up beyond its boiling point without bubble formation. This is called superheated water. When you take this water out of the microwave it moves and would suddenly boil and explode. THis is because it suddeny is disturbed and forms bubbles all over its body. Or if you put something like a fork inside it, the water meets the imprefections in the fork and explodes. This can be pretty dangerous.

      So superheated water is water which has exceeded its boiling point but does not have bubbles that carry away excess heat. It is on the edge of boiling. A small push would trigger boiling in the whole body in a very short time producing an explosion.

      Note that this does not always happen. SOmetimes water boils in a microwave quite nicely. It all depends on the kind of vessel you use for heating water.

      Technology may produce fancy things but nature always shows you that it is supreme. Take care with your microwave.

 

kanwar

 

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  Go, wondrous creature! mount where Science guides:                 

  Go, measure earth, weigh air, and state the tides:                 

  Instruct the planets in what orbs to run,                          

  Correct old time and regulate the Sun;                             

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VIRUS

 

      Today in VERITAS we will study something that is right on the boundary between the living and the nonliving. We shall study the virus.

      A living cell is one that is capable of independent existence. i.e it can eat, grow and reproduce as an independent body. A virus cannot do that. A virus is as good as nonliving until it comes into contact with a cell which it can enter. So a cold virus may exist in the air for a long long time just not doing anything … not living. But as soon as it comes in contact with a host cell it comes to life and uses the machinery of the host cell to produce more of its kind. Many biologists view the virus as a nonliving infectious particle.

      Viruses do not need any energy. No food for them ! They just need a host cell in which they can produce more viruses.

      So you can view a virus as a complex chemical that has only one aim: to produce more of its kind. It needs nothing else.

      A virus contains a set of genetic instructions( DNA or RNA) and a coat of protein that surrounds and protects these genetic instructions. Some viruses have an additional lipid coat around the protein coat.

      Viruses just stay motionless for long periods. As soon as a virus comes into contact with a host cell it comes to life. Viruses come to life only when they come in contact with specific cells.

A common cold virus infects your respiratory system and has no effect on your skin.  Similarly a plant virus cannot infect an animal cell.

The protein coat of the virus is sensitive to cells around it. This protein coat checks if it is in contact with a host cell which the virus can infect. As soon as the virus finds its host cell it attaches itself to the cell. The virus’s genetic meterial is injected into the cell. The genetic meterial takes over the host cell. It uses the enzymes of the host cell to make more virus. When all the cell’s resources have been used up the viruses break up the cell’s wall and escape to see if the neighbouring cells are possibe hosts. If they are then these are invaded too. The viral infection begins.

        The human body is smart too. As soon as a viral infection starts the cells around the infected area produce substances called interferons.

These interferons increase the resistance of the cells around the area and do not allow the infection to increase. This works most of the time. We do not fall ill every day even though we are being constantly invaded by viruses. Only if the interferons cannot control the spread does the immune system takes over the defence and we fall ill.

 The body produces chemicals called pyrogens. These pyrogens increase the temperature of the body. When the temperature of the body increases above the normal 98 degrees the cell processes become slower. This slow down of the cell processes slows down the reproduction of the virus as well. In addition to slowing down the cells of the body, the immune system kills the viruses and also the cell’s infected by the viruses. After a few days the viruses are checked and we become okay.

      THe HIV virus is a very dangerous virus. It infects the cells of the immune system. The other cells of the immune system starts destroying the infected immune system cells. The immune system cells decrease and other infections attack the body.

 

  A little poem by Ogden Nash:

 

            A Mighty Creature

 

      A mighty creature is the germ

      though smaller than a pachyderm.

      His customary dwelling place

      is deep within the human race.

      His childish pride he often pleases

      by giving people strange diseases.

 

Kanwar

 

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  Go, wondrous creature! mount where Science guides:                 

  Go, measure earth, weigh air, and state the tides:                 

  Instruct the planets in what orbs to run,                           

  Correct old time and regulate the Sun;                             

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