Magnetic or not?

Many iron and steel objects are magnetised without one realising it. You can detect this magnetism with a compass.If a rod is magnetised, it must, like the compass needle, have a north and South Pole. 

Since two unlike poles attract and two like poles repel, one pole of the needle will be attracted to the endofthebarandtheotherrepelled.Ifthebarisnotmagnetised, both poles of the needle are attracted to the end.

The earth’s magnetic field

Hold a soft iron bar pointing to the north and sloping downwards, and hammer it several times. It will become slightly magnetic.

The earth is surrounded by magnetic field lines, which meet the earth in Great Britain and NorthAmerica at an angle between 60 and 80-degrees. 

When the iron is hammered, its magnet particles are affected by the earth’s magnetic field lines and point to the north. In a similar way, tools sometimes become magnetic for no apparent reason. If you hold a magnetised bar in an east-west direction and hammer it, it loses its magnetism

Flash of Lightning

Place a metal slice on dry glass, and on it a piece of hard foam plastic which you have rubbed well on your pullover. If you hold your finger near the handle of the slice, a spark jumps across.

When the negatively charged plastic is placed on the slice, the negative electric particles in the metal are repelled to the end of the handle, and the voltage between it and the finger becomes equalised. 

Plastic materials can become strongly charged. In warehouses, for example, metal stands for rolls of plastic are earthed because otherwise they often spark when by the personnel.

High Voltage

Place a flat baking tray on a dry glass, rub a blown-up balloon vigorously on a woollen pullover and place it on the tray. If you put your finger near the edge of the tray, a spark jumps across.

A voltage equalisation occurs between the metal and the finger. Although the spark is discharged with several thousand volts, it is just as harmless as the sparks produced when you comb your hair.

An American scientist discovered that a cat’s fur must be stroked 9,200.000.000 times to produce a current sufficient to light a 75-watt bulb for a minute.

Puppet Dance

Lay a pane of glass across two books, with a metal plate underneath. Cut out dolls an inch or so high from tissue paper. If you rub the glass with a woollen cloth, the dolls underneath begin a lively dance. 

They stand up, turn round in a circle, fall, and spring up again.The glass becomes electrically charged when it is rubbed with the wool, attracts the dolls, and also charges them. 

Since the two like charges repel each other, the dolls fall back on the plate, give up their charge to the metal and are again attracted to the glass.

Electric Fleas

Rub a long-playing record with a woollen cloth and place it on a glass. If you toss some small silver-paper balls on to the record,theywilljumpawayfromoneanotherinazigzagmotion. 

If you then move the balls together with your fingers, they will hop fiercely away again.The electricity produced on the record by rubbing is distributed in irregular fields. 

The balls take up the charge and are repelled, but are again attracted to fields with the opposite charge. They will also be repelled when they meet balls with the same charge.

Electrical Ball Game

Fix a piece of silver paper cut into the shape of a footballer on to the edge of a phonograph record, rub the record vigorously with a woollen cloth and place it on a dry glass. 

Put a tin can about two inches in front of the figure. If you hold a small silver-paper ball on a thread between them, it swings repeatedly from the figure to the can and back.

The electric charge on the record flows into the silver-paper figure and attracts the ball, it becomes charged, but is immediately repelled because the charges become equal, and goes to the can, where it loses its electricity. This process is repeated for a time.

Simple Electroscope

Bore a hole through the lid of a jam jar and push a piece of copper wire bent into a hook through it. Hang a folded strip of silver paper, from which you have removed the paper, over the back. 

If you hold a fountain pen, comb, or similar object, which has been electrically charged by rubbing on the top of the wire, the ends of the strip spring apart.

On contact with a charged object, electrical charges flow through the wire to the ends of the strip. Both now have the same charge and repel one another according to the strength of the charge.

Shooting Puffed Rice

Charge a plastic spoon with a woollen cloth and hold it over a dish containing puffed rice. The grains jump up and remain hanging on the spoon until suddenly they shoot wildly in all directions.

The puffed rice grains are attracted to the electrically charged spoon and cling to it for a time. Some of the electrons pass from the spoon into the puffed rice, until the grains and the spoon have the same charge. Since, however, like charges repel one another, we have this unusual drama.

Water Bow

Once more rub a plastic spoon with a woollen cloth. Turn the water tap on gently and hold the spoon near the fine jet.At this point, the jet will be pulled towards the spoon in a bow.

The electric charge attracts the uncharged water particles.However, if the water touches the spoon, the spell is broken. Water conducts electricity and draws the charge from the spoon. 

Tiny water particles suspended in the air also take up electricity. Therefore experiments with static electricity always work best on clear days and in centrally heated rooms.

Coiled Adder

Cut a spiral-shaped coil from a piece of tissue paper about 4 inches square, lay it on a tin lid and bend its head up. Rub a fountain pen vigorously with a woollen cloth and hold it over the coil. 

It rises like a living snake and reaches upwards.In this case the fountain pen has taken electrons from the woollen cloth and attracts the uncharged paper. 

On contact,the paper takes part of the electricity, but gives it up immediately to the lid, which is a good conductor. Since the paper is now uncharged again, it is again attracted, until the fountain pen has lost its charge.

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.

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.