Category Modern Science

What is Osmosis?

               It is a well known fact that when resins are put in water they get swollen. This swelling takes place due to the entry of water through the membrane of the resins. Similarly, if grapes are put in sugar solution they shrink. Swelling of resins and shrinking of grapes take place due to a process known as osmosis. Do you know what this osmosis is?

               Osmosis is a process in which a solution of lower concentration passes into a solution of higher concentration through a semipermeable membrane. A semipermeable membrane is one that allows some, but not all, substances to pass through it. This contains very small pores. When resins are put into water, the covering acts as a semipermeable membrane. Water is less concentrated than the substance present inside the resins and so the water moves into the resins through its semipermeable membrane. Similarly, fluid from grapes moves out through the semipermeable membrane, as the concentration of sugar solution is more than that of the grapes. There is a tendency for solutions separated by a membrane to become equal in molecular concentration.

               In osmosis, the movement is always from a dilute solution into a solution of higher concentration. This reduces the concentration of the stronger solution. The rate of osmosis depends upon the comparative strengths of the two solutions. The greater the difference, the faster the rate of osmosis. This process continues until both solutions are of equal strength. When this equilibrium is reached, osmosis stops.

               Osmosis is an ongoing process among the living beings. The membranes of cells are semipermeable. Plants absorb water and dissolved minerals from the soil by osmosis; they use osmosis to move the water and dissolved minerals through the plant, cell by cell. Osmosis also maintains turgor pressure. Turgor pressure is the pressure of water on the cell. It gives the cell form and strength. When there is a decrease in turgor pressure, the plant will soon wilt and lose its regular stiffness.

               Osmosis allows the transfer of water and dissolved nutrients in the human body from the blood into the cells.

 

How do electrically heated appliances work?

Electric heaters, immersion heaters, electric irons, electric kettles, etc. are appliances which produce heat through electricity. All these appliances are based on the heating effects of electric current. When electric current is passed through a wire, it gets heated up. Heating of a wire depends upon two facts: first, on the resistance of the wire and then on the amount of electric current passed. The heat produced in the wire is directly proportional to the resistance of the wire and that of the square of the current. The amount of heat produced also depends upon the time for which the current passes through the wire.

Based upon this property of current, many domestic electric appliances have been developed. The working principle of all these appliances is almost the same, the difference lies only in their construction. An electric heater consists of a coil of nichrome wire which is in the form of a spring. This coil is mounted on an insulating base plate made of clay. When electric current is passed through the coil, it gets heated up. Room heaters are also made in a similar way, the only difference being that nichrome wire is wound around an insulating rod and a reflector is mounted at the back of the coil which reflects the heat radiation.

Immersion heaters also consist of a nichrome wire which is enclosed in a metal tube. To isolate the wire from the metal tube, an insulating powder is filled in the tube. This powder acts as an insulator for electricity but conducts heat. When the two terminals of the wire are connected to an electric source, the current starts flowing through the wire and it gets heated up. The immersion heater is put inside a bucket full of water to heat the water.

An electric iron is used to remove the wrinkles from washed clothes. This appliance also consists of a ribbon of nichrome wire which is enclosed between two sheets of mica. This spreads the heat uniformally along the base plate of an electric iron. Mica sheets are mounted on a heavy metal plate. This metal plate, when pressed against the surface of the cloth, removes the wrinkles from the cloth.

Electric irons are of two types: automatic and manual. Automatic one is fitted with a thermostat control which regulates the temperature. Manual irons do not have such a device. When the iron is cold, thermostat provides and maintains a constant temperature by the use of a device that cuts off the supply of heat when the required temperature is exceeded.

An electric kettle is used to prepare tea or coffee. It also consists of a heating element fitted at the bottom of the vessel and is isolated from it. Water is put into the vessel which gets heated when current is passed through the heating element.

For all electrically heated appliances, it is very essential to have an earth connection. Immersion heaters should not be switched on, until there is water in the bucket. The electric bulb is also a similar device whose filament gets heated up when the electric current is passed through it and it produces light.

 

How do a mixer and grinder work?

               Mixer and grinder are very useful domestic appliances. With the help of these appliances we can grate, grind and prepare mango shake, milk shake, cold coffee etc. in a short period of time. Butter can be extracted from cream by using this apparatus. Pulses and spices can also be ground easily with its help.

               This apparatus consists mainly of two parts. One is the base of the apparatus which is fitted with a high speed motor. This motor makes 15-20 thousand revolutions per minute. It also consists of a variable switch by which the speed of the motor can be adjusted with the other part of the apparatus known as a mixer and grinder. This is usually made of stainless steel or plastic in the shape of a jar. It is fitted with blades which revolve with the speed of the motor. This rotating blade minces the food material into small pieces.

               Modern mixer and grinders also consist of other attachments such as a juicer with the help of which we can extract the juices of apples, oranges, tomatoes and other fruits and vegetables. In this attachment juice pours out on one side and pulp from the other side. Most modern grinders and mixers can be fitted with various other attachments such as a slice grater, meat mincer, dough maker etc. Nowadays we have grinders by which even wheat or maize can be ground.

               These electrically operated machines have minimized the tedious work in a kitchen. Not only do these machines save time but also provide neat, clean and tasty food for us. Moreover, these machines do not consume much electricity.

What is a Robot?

          A robot is an automatic machine which can work like a human being. It can replace man in various branches of scientific and industrial tasks because it does not suffer from human limitations. It may or may not resemble a human being but definitely can work like a human being. The robots which resemble humans are called androids.

          The word ‘robot’ was first used in the play ‘Rossum’s Universal Robots’ by the Czechoslovak dramatist, Karel Capek, who had derived it from a Czech, word ‘Robota’ which means a forced or bonded labourer.

          The industrial revolution and automations stimulated the invention of robotic devices to perform certain human tasks. A human worker, however superb a craftsman he may be has certain limitations. He cannot work continuously in a hostile environment. He cannot work for long periods because he gets tired. He may be in short supply and may be expensive to hire. Modern industrial robotic devices aim to substitute a machine for man in hostile environments, cut costs by replacing expensive hand labour with cheap dependable machines, and provide versatile, all purpose robots or mechanical devices at predictable costs. Robot is such a machine which does not get tired, does not go on strike and does not demand increase in salary. 

          Robots can perform a variety of jobs such as welding and painting a car, house cleaning, cutting the grass of a lawn, working in nuclear plants or travelling to space. They can also play chess, work as a watchman, cut the wool of a sheep and pluck fruits from trees.

          Robots of higher level are capable of adapting to changes in environment. They are also capable of making decisions with the help of computers. A more complex robotive device in modern transportation is the automatic aircraft pilot which can control routine flights. An android robot named Shaky Robot was developed at Stanford Research Institute in California to do a variety of research jobs.

          Japan has the largest number of robots in the world. The United States of America, Britain, Germany, Sweden, Italy, Poland, France, India, etc are also using robotic devices for different purposes. All robotic devices are controlled by computers.

 

Can air be converted into a liquid?

Scientists have developed techniques through which gases like nitrogen, oxygen, hydrogen, and helium can be converted into liquids. These techniques involve cooling of the gas to a certain temperature called the critical temperature and then it is compressed to a very high pressure. Due to this cooling and compression the molecules of the gas come closer and the gas gets converted into a liquid. Air is a mixture of nitrogen, oxygen and other gases and can be liquefied by cooling it to about -200°C at normal atmospheric pressure. Under high pressure it can be liquefied at about -141°C.

The technique used for the liquefaction of air is shown above. Through this technique the air from the atmosphere is compressed to a high pressure. This air is then allowed to expand rapidly. As a result, the air gets cooled to a very low temperature. Its heat is lost due to the sudden expansion. This cool air is compressed further by which it gets converted into liquid.

Liquid air is very cool. It is a mixture of liquid oxygen which boils at -183 °C, liquid nitrogen which boils at -196°C and liquid argon which boils at -186 °C. It is bluish in colour and is kept in special vacuum flasks. It is mainly used in research laboratories to produce low temperatures.

Liquid hydrogen boils at -253°C. It is cooler than liquid air. Liquid helium is still cooler. It boils at -269°C. All the liquid gases should be handled with care. If they fall on your skin they may damage the body cells. If a rubber tube is inserted in liquid air it becomes as hard as a wooden stick. 

How does soap clean things?

           Ordinary water does not remove dirt from things because grease and water do not mix. So soap is one of the most common cleansing agents used all over the world. People use soaps and detergents to clean their skin, clothes, utensils and many other objects. How does soap remove dirt?

          Soap is basically a fatty acid salt which can be obtained by boiling fats or oils together with an alkali. When oil is allowed to react with caustic soda solution, the chemical reaction produces soap and glycerin. Both are separated. When soap is applied on a cloth, its molecules break into fatty acid ions and sodium ions. Fatty acid ions are repelled by water but are attracted towards greasy dirt particles. They surround each grease molecule and remove it from the surface of the cloth. These are carried away by the water and consequently the cloth gets cleaned. Other actions, such as agitating, squeezing or rubbing and rinsing help loosen dirt and grease so that water may carry them away.

          Today, chemical cleaners called detergents are more and more in use instead of ordinary soaps. Detergents clean better than soaps in hard water, (the ‘hardness’ of the water is caused by the presence of calcium and magnesium salts. Soap does not make much lather in hard water) but they do not, by themselves, make suds. Suds are not necessary for cleaning but substances that make suds are added to detergents.

          Many substances are added to a crude soap to make it suitable for use as toilet soap. Coconut oil is added to make it lather quickly. Dyes, perfumes, water softeners and germicides, which are tiny substances that kill germs, are also added.