Your are here:Home > Science Popularisation

Science in Action August 5 - 7, 2005

Kannada Version : Part 1      Part 2

 A view of the eager students Inauguration by Prof. S. Lokanathan Discussion on the exhibit

For a brief description of the experiments displayed at the Science in Action, organized by Bangalore Association for Science Education at Jawaharlal Nehru Planetarium during August 5 - 7 2005

SIMPLE MOTOR

Things required:
enamelled copper wire, 1.5V cell, a magnet, metal strips with holes at one end (stove pins will do)

Procedure:
Make a coil of about fifty turns out of copper wire. Straighten up the ends so that they jut out diametrically opposite each other. Now scrape off all the varnish from one end. On the other end, scrape the varnish only from three sides, leaving the insulation intact on one side.

The little strip of insulation acts like a switch. Next, put the ends of the coil in the holes of stove pins. Place a magnet beneath the coil.

Observation:
As the current flows through the coil, the coil rotates rapidly.

Reason:
A conductor carrying current in a magnetic field experiences a mechanical force, as predicted by the Fleming's Left Hand Rule.

Further exploration:
Investigate the effect of the following factors on the speed of rotation: number of turns, thickness of the wire, strength and orientation of the magnet, potential difference applied.

BOILING WATER UNDER PRESSURE

Things required:
Hot water, syringe with a piston

Procedure:
press the piston all the way down into the syringe. Now, slowly draw hot water, a couple of degrees below boiling point, into the syringe. When it is about half-filled, take the syringe out and quickly
draw up the piston.

Observation:
The hot water inside the syringe begins to boil!

Reason:
The pressure inside the syringe falls when the piston is quickly drawn out. Under reduced pressure, water boils at a lower temperature Further exploration: Does water boil, if the piston is drawn out slowly?

A CLOCK REACTION

Things required:
Mercuric chloride, potassium iodate, starch Procedure: Preparation. The following three solutions need to be prepared.

1. Make a paste of 4 g of soluble starch with a little water. Pour onto this 500ml of
boiling water and stir. Cool it to room temperature, add 13.7 g of sodium
metabisulphite (Na2S2O5) and make up to 1 l with water.

2. Dissolve 3 g of mercury(II) chloride in water and make the solution up to 1 l with
water.

3. Dissolve 15 g of potassium iodate (KIO3) in water and make the solution up to 1 l
with water.

Demonstration.
Mix 50 ml of solution A with 50 ml of solution B. Then pour into this mixture 50 ml of solution C. After about 5 seconds the mixture will turn an opaque orange colour as insoluble mercury iodide precipitates. After further 5 seconds the mixture suddenly turns blue-black as a starch-iodine complex is formed.

The second colour change (orange to black) is not normally expected by the audience and
comes as a real surprise.

PEPPER'S GHOST

Things required:
A bulb, a sheet of glass, a box and a glass of water

Procedure:
Place a sheet of plexiglass along the diagonal of the box.Switch on the bulb. You will see the bulb glowing under water in the glass container!

Explanation:
The sheet of glass divides the box into two compartments - one of which has a glass of water and the other has the bulb. They are positioned in such a way that the image of the bulb and the glass of water are superimposed. This gives us the impression of a bulb glowing under water. Here, we use the fact that glass reflects a fair amount of light when it viewed at an angle of about 45 degrees to our line of sight.

Further exploration: This effect does not work if the glass is dusty. Why?

ACID RAIN INDICATOR

Things required:
Red cabbage leaves or blue berry, vinegar, baking soda, jars

Procedure:
Chop some red cabbage leaves and boil them in distilled water for about ten minutes. Then filter out the purple coloured liquid. Pour out the liquid into two jars. Add baking soda to one of the jars and
vinegar to the other.

Observation:
The soda jar turns green and the vinegar jar pink.

Reason:
The red cabbage juice acts as an indicator. It changes its colour to green in alkali medium and pink in acidic medium. This property can be used to check if the rain water is acidic.

Further Exploration:
Start with 100 ml of water. Add red cabbage juice to it. Now add vinegar drop by drop. How many drops of vinegar is required for the cabbage extract to turn pink? Why does the pink colour appear soon after adding the first drop?

DANCING NAPHTHALENE BALLS

Things required:
Naphthalene balls, baking soda, lemon juice

Procedure:
Fill up a gas jar with water and add naphthalene balls to it. They will sink to the bottom of the jar. Now, add some lemon juice and baking soda to water.

Observation:
The naphthalene balls begin to bob up to the surface and then come down. This kind of motion repeats.

Reason:
The naphthalene balls sink in water because their density is greater than that of water. The reaction between lemon juice ie citric acid and baking soda ie sodium bicarbonate results in the liberation of carbon dioxide. Bubbles of CO2 settle on the surface of the balls, thereby decreasing its density. When the balls rise to the surface, the bubbles break and the balls sink.

A DIODE SWITCH

Things required:
a semiconductor diode, IN 4001, a resistor, an LED, 1.5V cell

Procedure:
Make the electric connections as shown in the circuit. When the circuit is closed the LED does not glow even though there is no break in electrical contacts. Now, connect the diode with opposite polarity.

Observation:
The LED glows

Reason:
A diode is a two terminal semiconductor device. It has a pterminal and an n-terminal. It conducts current only if the p-terminal is connected to the positive terminal of the battery. The LED only glows when the diode conducts current. This way a diode acts like a switchconducting current only when connected in one way.

THE INVISIBLE BEAKER

Things required:
two beakers of different diameters and glycerine Procedure: Place the smaller beaker inside the larger one. The two beakers can be seen clearly. Now add glycerine into the gap between the two beakers.

Observation:
The smaller beaker becomes invisible!

Reason:
The refractive index of the material of the beaker and that of glycerine are almost the same. On account of this much of the light is transmitted and hardly any light reflected by the smaller beaker reaches our eye.

FORMATION OF STALAGMITES

Things required:
Two beakers, water, cotton thread, cardboard box, two nails and epsom salt (magnesium sulphate).

Procedure:
Prepare a saturated solution of epsom salt in water. Pour it into the two glasses. Place the two glasses on either side of the box. Tie the nails to the ends of the thread and dip the two ends in epsom salt solution in the two glasses.

Observation:
A while later, we observe the salt solution slowly rising up the thread from both ends. This is how stalactites begin in nature. When enough solution collects along the thread, it drips down into the box. This is how stalagmites are formed.

Reason:
The salt solution rises up the thread by capillary action.

MARIOTTE VESSEL

Things required:
plastic bottle, glass/ plastic tube, single-holed rubber cork, beaker, clock

Procedure:
Make a hole at C in the plastic bottle, as shown in the diagram. Fill the bottle with water and allow it to flow through C. Fill up the bottle with water again and close the outlet C. Now close the mouth of the bottle with the rubber stopper and pass the glass pipe through it such that the bottom of the pipe is at B. On opening the outlet, water flows out.

Observation:
The rate at which the water flows out continuously decreases in the first case while water flows at a constant rate until the level reaches B in the second, even though the water level at the top is reducing.

Reason:
Due to the introduction of the pipe, the pressure at B is still equal to atmospheric pressure. The rate of flow of water depends only on the depth BC. This remains constant until the water level crosses B. Thereafter, the flow rate is decided by the water level.

CENTRIFUGE

Things required:
a magnetic stirrer, beaker, plant seeds of different densities

Procedure:
Fill three-fourths of the beaker with water and sprinkle samples of seeds of different densities on it. Place the beaker on the stirrer platform. Switch on the stirrer. Water as well as the seeds begin to swirl.

Observation:
Concentric circles of seeds of varying densities are seen.

Reason:
A centrifuge separates particles based on density. Less dense particles collect closer to the centre of revolution and the more dense ones farther from it.

EYE DEFECT

Things required:
Concave and convex lenses, lens holders, screens, laser pointers, incense sticks, smoke chamber with glass shutters

Procedure:
The lens holder, laser pointer holder and screens are placed in position. Incense sticks are lit and placed inside the smoke chamber to create and trap smoke. On placing a convex lens in the holder, we can see parallel beam of light converging after passing through the lens but short of the screen ('retina'). By placing a suitable concave lens, the light rays are made to come to focus on the screen.

ELEVATOR

Things required:
one plywood sheet about two feet by one foot, six cotton thread reels, six nails, cardboard box, string, a small weight

Procedure:
Arrange the reels and the box with strings as shown in the diagram. Turn the spool 2 with your fingers.

Observation:
The car will go up or down depending on the direction of rotation of the windlass spool 2.

DIFFUSION OF GASES

Things required:
glass tube, pH paper, litmus paper, cotton wool, volatile liquids.

Procedure:
Take a series of glass tubes open at both ends, which can be sealed using corks. Damp pH paper is placed at different distances along the inside of the tube. The tube is clamped horizontally and maintained at different temperatures and with different volatile liquids.

Observation:
The colours of the pH papers change

Reason:
The molecules of volatile materials diffuse and react with the chemicals on the pH paper. The diffusion takes place in either direction from a region of high concentration to one at a lower concentration.

EFFECTS OF ELECTRIC CURRENT

Things required:
two 1.5V cells, thick copper wires, dilute H2SO4, magnetic compass, bulb, crocodile clips and connecting wires.

Procedure:
Make the connections as shown in the circuit diagram. The glowing bulb shows the heating and lighting effect. The deflection in the compass shows demonstrates the magnetic effect and the bubbles of gas
indicate the chemical action of electric current.

LUNG CAPACITY

Things required:
a tub, marker, ruler, two wooden blocks, a glass jar and a rubber tube.

Procedure:
fill the tub with two-thirds of water. Place the glass jar on the two wooden blocks in the tub such that no water has entered the jar. Insert a rubber tube into the inverted glass jar. Exhale completely and suck air in one breath from the other end of the pipe.

Observation:
Water rises into the jar.

Reason:
As air is removed from the jar, pressure inside it reduces so water enters the jar. The volume of water that enters the jar will be equal to the volume of air removed it. That is, the volume of air that fills our lungs

ELECTROMAGNETIC INDUCTION

Things required:
An agarbathi tube, insulated copper wire, LED and a strong bar magnet

Procedure:
Wind about 200 turns on the tube with enamelled copper wire. Connect the ends of the wire to an LED. Now, take a bar magnet and insert into the tube quickly and withdraw it.

Observation:
The LED glows for a short duration.

Reason:
The moving magnet induces a current in the coil that lights up the LED.

SURFACE TENSION OF WATER

Things required:
a beam balance with two pans, nails, a beaker, weights and water

Procedure:
Suspend pans on either ends of the beam balance. Gently bring one of the pans in contact with water surface. Now go on adding weights in the other pan. After adding a certain weight, the pan in contact with water detaches from the water surface.

Reason:
The pan is held to the water surface primarily on account of surface tension of water. Once the weight in the other pan is slightly greater than the surface tension, the pan 'sticking' to the water surface is released.

CHEMICAL COPYING

Things required:
turpentine, water, soap, newspaper

Procedure:
Mix four parts of water with one part of turpentine. Add a small quantity of soap to it and shake the mixture. Soon, the soap dissolves. Now, if you want to copy a photograph from a newspaper, wet the newspaper a little with the mixture. Place a white sheet of paper on it and rub the paper strongly with a spoon. The turpentine dissolves enough with the ink and you will find a picture printed in reverse.

POLYMERIZATION

Things required:
urea, formalin, concentrated suplhuric acid, plasticine clay.

Procedure:
Add about 10g of urea to about 20 cc of formalin in a plasticine clay 'vessel'. Add a few drops of concentrated H2SO4. Within a minute, the solution begins to go milky and eventually a hard white substance is formed. This is a polymer called urea formaldehyde.

Explanation:
The chemical reaction takes place according to the equation given here. A polymer is a long chain molecule that has one unit being linked a number of times through covalent bonds. Many of the proteins as well as synthetic materials are polymers.

CONSERVATION OF ENERGY

Things required:
Iron stand with clamp, string, pendulum bob and a ball point pen

Procedure:
Tie the bob to one end of a half metre string. Suspend this from the end of a clamp. Gently pull the bob to an extreme position and release it. Observe the maximum height to which it goes at the other extreme. It will be nearly the same. Now repeat the above step with a ball point pen acting as an
obstacle to the string.

Question: Does the bob go up to the same height from which it was released?

Observation:
Yes. It does- Contrary to popular expectation!.

Reason:
Eventhough the bob is not allowed to reach the other extreme position by the ballpoint pen, the potential energy stored in the bob is not diminished in any way. So, the bob may not go to the other extreme position it did the first time but it does go up to the same height from which it was released. This is based on conservation of energy.

FLUORESCENCE

Things required:
Liquid soap, water, washing blue, ultraviolet lamp

Procedure:
Mix equal quantity of liquid soap and water. Use this as 'paint' to draw a scenery or write down a message on a white sheet of paper. Let the paper dry. The drawing or the message can hardly be read. Now, place the sheet of paper in front of a UV lamp. The message glows!!!

Reason: Soaps usually contain what are popularly known as 'whiteners'. These substances absorb UV light and emit a faint light. The colour of the emitted light depends on the chemical nature of the molecules used as whitener. This property of absorbing radiation and re-emitting in another form is termed as fluorescence. Washing blue usually have such whiteners that give sparkle to the cloth even
if the dirt is not completely removed!

DECOMPOSITION OF HYDROGEN PEROXIDE

Things required:
hydrogen peroxide, copper mesh, bunsen burner

Procedure:
Heat the copper mesh and gently introduce it into a boiling tube containing hydrogen peroxide.
Observation: Bubbling is immediately noticed.

Reason:
The bubbles are oxygen that is released due to decomposition of hydrogen peroxide. The peroxide decomposes into water and oxygen. At room temperature, this is a very slow process. Heated copper acts as a catalyst. Introducing a burning splinter into the boiling tube can show that oxygen is released. It burns brightly.

Further exploration:
Introduce mesh of different metals into the peroxide and check if heat is responsible for the decomposition. Dynamo

DYNAMO

GEARS

Things required:
two wooden rods, two circular wooden pieces with 20 teeth and one circular wooden piece with sixty teeth, motor of a suitable capacity, a 9V battery, toy steering rod, rectangular wooden piece with sixty teeth, two toy wheels.

Procedure:
Fix the circular wooden pieces to the rod that serves as an axle. Mount the two rods on a wooden board and fix two motors to each axle and connect them to a battery through a two-way switch. When the smaller gear called the pinion rotates the larger gear, the power is more but the speed of rotation is less as while starting an automobile. When the larger gear moves the pinion, the power is less but the speed of rotation is more. The change in speed depends on the number of teeth in the pair of gears. A steering wheel is fixed to one side of a rod and rotating disc on the other end of the rod. The rotating disc is assembled as in rack gear which is connected to the wheels of an automobile. The wheel in the direction of the steering while the gears move in opposite direction.

SEEING THE HEART BEAT