25. Burning without a flame

Press a handful of steel wool firmly into a glass tumbler and moisten it. Invert the tumbler over a dish containing water. At first the air in the tumbler prevents the water entering, but soon the level of water in the dish becomes lower while that in the glass rises.

After the steel wool is moistened, it begins to rust. The iron combines with the oxygen in the air, and we call this process combustion or oxidation. Since the air consists of about one-fifth oxygen, the water rises in the tumbler until after some hours it fills one-fifth of the space.

However, an imperceptible amount of heat is set free in the process.



26. Burning iron

Would you have thought that even iron could be made to burn with a flame!

Twist some fine steel wool round a small piece of wood and hold it in a candle flame. The metal begins to blaze and scatter sparks like a sparkler.

The oxidation, which was slow in the previous experiment, is rapid in this case. The iron combines with the oxygen in the air to form iron oxide. The temperature thus produced is higher than the melting point of iron. Because of the falling red-hot particles of iron it is advisable to carry out the experiment in a basin.

Reserved



27. Destroyed metal

Put a piece of aluminum foil with a copper coin on it into a glass of water, and let it stand for a day. After this the water looks cloudy and at the place where the coin was lying the aluminum foil is perforated.

This process of decomposition is known as corrosion. It often occurs at the point where two different metals are directly joined together. With metal mixtures (alloys) it is particularly common if the metals are not evenly distributed. In our experiment the water becomes cloudy due to
dissolved aluminum. A fairly small electric current is also produced in this process



28. Electricity Potato battery

Stick finger-length pieces of copper and zinc wire one at a time into a raw potato. If you hold an earphone on the wires, you will hear distinct crackling.

An electric current causes the noise. The potato and wires produce an electric current in the same way as a torch battery, but only a very weak one. The sap of the potato reacts with the metals in a chemical process and also produces electrical energy. We speak of a galvanic cell because the Italian doctor Galvani first observed this process in a similar experiment in 1789.



29. Coin current

Place several copper coins and pieces of sheet zinc of the same size alternately above one another, and between each metal pair insert a piece of blotting paper soaked in salt water. Electrical energy, which you can detect, is set free. Wind thin, covered copper wire about 50 times round a compass, and holds one of the bare ends on the last coin and one on the last zinc disk. The current causes a deflection of the compass needle.

In a similar experiment the Italian physicist Volta obtained a current. The salt solution acts on the metal like the sap in the potato in the previous experiment.



30. Graphite Conductor

Connect a torch bulb with a battery by means of a pair of scissors and a pencil. The bulb lights up. From the long tongue of the battery, the negative pole, the current flows through the metal of the scissors to the
lamp. It makes it glow, and flows through the graphite shaft to the positive pole of the battery. Therefore graphite is a good conductor: so much electricity flows even through a pencil “lead” on paper, that you can hear crackling in earphones.



31. Mini-microphone

Push two pencil leads through the short sides of a matchbox, just above the base. Scrape off some of the surface, and do the same with a shorter lead, which you lay across the top. Connect the microphone with a battery and earphone in the next room. (You can take the earphone from a transistor radio.) Hold the box horizontal and speak into it. Your words can be heard clearly in the earphone.

The current flows through the graphite “leads”. When you speak into the box, the base vibrates, causing pressure between the “leads” to alter and making the current flow unevenly. The current variations cause vibrations in the earphone.

32. Mysterious Circles

Push a length of copper wire through a piece of cardboard laid horizontally and connect the ends of the wire to a battery. Scatter iron filings on to the cardboard and tap it lightly with your finger. The iron filings form circles round the wire. If a direct current is passed through a wire or another conductor, a magnetic field is produced round it. The experiment would not work with an alternating current, in which the direction of the current changes in rapid sequence, because the magnetic field would also be changing continuously.



33. Electro- magnet

Wind one to two yards of thin insulated wire on to an iron bolt and connect the bare ends of the wire to a battery. The bolt will attract all sorts of metal objects.

The current produces a field of force in the coil. The tiny magnet particles in the iron become arranged in an orderly manner, so that the iron has a magnetic north and South Pole. If the bolt is made of soft iron, it loses its magnetism when the current is switched off, but if it is made of steel it retains it.

Electro Buzzer

(Please See Image Above)

Nail board B and wooden blocks C and D onto board A (about 5 X 5 inches). Push an iron bolt F through a hole bored in B. Wind covered copper wire G 100 times round the bolt and connects the ends to a battery and to H respectively. Bore a hole through block C and wedge the fret saw blade H firmly into it so that its end is a short distance from bolt F. Hammer a long nail K through A and bend it so that its point rests in the middle of the saw blade. Oil the point of the nail. Use a piece of beading E as a key, with a rubber band P as spring and drawing pins M and N as contacts. Join all the parts with connecting wire (remove the insulation).

If you press the key down, you connect the electric circuit, bolt F becomes magnetic and attracts H. At this moment the circuit is broken at K and the bolt loses its magnetism. H jumps back and reconnects the current. This process is repeated so quickly that the saw blade vibrates and produces a loud buzz. If you wish to do Morse signaling with two pieces of apparatus, you must use three leads as in the lower circuit diagram.

hmmmmm .. thanxx



35. Light fan

Hold a light-coloured rod between your thumb and forefinger and move it quickly up and down in neon light. You do not see, as you might expect, a blurred, bright surface, but a fan with light and dark ribs.

Neon tubes contain a gas, which flashes on and off 50 times a second because of short breaks in alternating current. The moving rod is thrown alternatively into light and darkness in rapid sequence, so that it seems to move by jerks in a semicircle. Normally the eye is too slow to notice these breaks in illumination clearly. In an electric light bulb the metal filament goes on glowing during the short breaks in current.



36. Clinging balloons

Blow up some balloons, tie them up and rub them for a short time on a woollen pullover. If you put them on the ceiling, they will remain there for hours.

The balloons become electrically charged when they are rubbed, that is, they remove minute, negatively charged particles, and called electrons, from the pullover. Because electrically charged bodies attract those, which are uncharged, the balloons cling to the ceiling until the charges gradually become equal. This generally takes hours in a dry atmosphere because the electrons only flow slowly into the ceiling, which is a poor conductor.



37. Pepper and salt

Scatter some coarse salt onto the table and mix it with some ground pepper. How are you going to separate them again?

Rub a plastic spoon with a woollen cloth and hold it over the mixture. The pepper jumps up to the spoon and remains sticking to it. The plastic spoon becomes electrically charged when it is rubbed and attracts the mixture. if you do not hold the spoon too low, the pepper rises first because it is lighter than the salt. To catch the salt grains, you must hold the spoon lower.