Category Everyday Science

Magnets are objects that produce an invisible force called magnetism. When two magnets are close to each other they produce pushing or pulling forces on one another. Magnets can also pull on, or attract, other objects that are made of magnetic materials, such as iron. Magnets are often U-shaped, like a horseshoe.

Magnetic poles

Magnets have two ends, or poles, called a north pole and a south pole. Unlike poles pull on each other, or attract, so a north pole pulls a south pole. Like poles push on each other, or repel, so a north pole pushes another north pole away.

Magnetic materials

Iron is a magnetic material, so any metal with iron in it, such as steel, will be attracted to a magnet. Nickel and cobalt are also magnetic metals.

Non-magnetic materials

Magnets have no effect on non-magnetic materials. Non-magnetic materials include all non-metals, such as glass, plastic, or wood. Most metals are also non-magnetic, including gold, aluminium, and copper.

 

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An electrical circuit is a loop around which electrical energy can move. Electricity travels from a power source, such as a battery, through wires, and back to the power source. In a simple circuit, other useful items that make use of the electricity, such as a bulb or a buzzer, are added. Electricity can only flow when there is a complete circuit.

Battery

A battery stores electrical energy and releases it when connected to a circuit. The battery will eventually run down and will have to be replaced.

Switch

A switch allows the bulb to be turned on or off without removing the battery. When the switch is closed, the circuit is complete and the bulb lights up.

Wires

Electricity flows around the circuit through a series of wires. Wires are usually made of copper, as copper is a good conductor of electricity.

Bulb

As electricity flows through the bulb, the electricity energy is converted to light energy, and the bulb glows brightly.

Conductors and Insulators

Conductors allow electricity to flow easily through them. Metals, such as copper, are good conductors of electricity. Electrical wires are made of metal so electricity can flow easily through them. Insulators do not let electricity pass through them. Plastic, rubber, and wood are good electrical insulators. Wires are coated in plastic to prevent you from getting an electric shock if you touch them.

Switching on!

Many electrical items do not need batteries as they can be plugged into the mains, using a long wire. Once they have been plugged in, these items are usually turned on by passing a switch, which completes the electrical circuit.

 

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Glaucoma is a group of eye conditions that damage the optic nerve, the health of which is vital for good vision. This damage is often caused by an abnormally high pressure in your eye. Many forms of glaucoma have no warning signs. The effect is so gradual that you may not notice a change in vision until the condition is at an advanced stage.

Glaucoma is the result of damage to the optic nerve. As this nerve gradually deteriorates, blind spots develop in your visual field. For reasons that doctors don’t fully understand, this nerve damage is usually related to increased pressure in the eye.

Glaucoma tends to run in families. In some people, scientists have identified genes related to high eye pressure and optic nerve damage. Promptly go to an emergency room or an eye doctor’s (ophthalmologist’s) office if you experience some of the symptoms of acute angle-closure glaucoma, such as severe headache, eye pain and blurred vision.

 

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Lakes in cold region freeze in winter. What happens to the fish and other animals living in the lake?

A lake may freeze when it is very cold but fortunately for the fish and other animals living in it, it freezes only at the surface. The water below the surface remains unaffected. This happens because of the odd behaviour of water. Like any substance water also contracts and becomes denser as it cools; but once it cools to 4  its behaviour changes. Below 4  water actually starts becoming lighter. At 0 , water freezes to ice. Ice is lighter than water and it floats on water. The ice layer insulates the water below from the cool air above. This keeps the water below the surface, warm and in liquid state.

 

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My friend had a small magnet and he warned me not to use it to pull things towards it too often as that would exhaust its magnetic powers.

Can a magnet become demagnetized by overuse?

In materials like iron, the atoms themselves are little magnets. In the natural or neutral state, these atoms all point in different directions. In a magnet, the atoms all point in the same direction.

To de-magnetise a magnet, the alignment of the atoms needs to be disturbed in such a way that they are pointing randomly in different direction, as in the neutral metal. This can be done in either of three ways:

(a) by heating the magnet over a gas flame.

(b) by hammering it for a few minutes, or

(c) by dropping the magnet from a height of over 100 ft.

The magnet cannot lose its magnetic properties due to over use.

 

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The electric train gets electricity from an overhead wire. But how does a train running underground obtain electricity? The electric train has a device called a pantograph through which it draws electricity from a live wire above the tracks. In a suburban train 3 or 4 pantographs are used to run electric motors located in various compartments.

But in many underground train systems, the current is not obtained from an overhead wire. Instead, a third rail that runs parallel to the existing two, is laid and charged with electricity. The train picks up electricity from this track. This is done to reduce the height of the tunnel. In India, the Calcutta metro railway is an example of such an arrangement. Abroad, it is used in the London Underground.

 

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My friend says his uncle has invented a machine that once started can run forever without any assistance or additional energy. Are there such machines?

Many scientists have tried to build perpetual motion machines but without success. The force of friction ultimately brings every moving thing to a stop. So far the only machine that comes close to being a perpetual motion machine, is an artificial satellite circling the earth. It circles the planet for years but ultimately friction with dust particles slows it down and it falls into the upper atmosphere where t burns up.

 

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Glass is a bad conductor of heat. If a glass vessel is heated directly over a flame, the heat is not readily conducted to other parts of the vessel and even at the point of contact with the flame, the inside surface does not get as hot as the outside surface.

Consequently the outside surface expands more than the inside surface and the unequal expansions cause the glass to crack.

To avoid this the glass vessel is usually heated by keeping it on a wire gauze made of a good conductor of heat such as iron or copper. This ensures that heat is transferred indirectly and slowly to the glass vessel and the vessel does not crack.

 

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The ink is stored in the barrel of the pen. When we start writing, the ink flows down and collects at the hole near the middle of the nib. When we press the nib against the paper while writing, the slit in the nib opens slightly and behaves as a very narrow tube or capillary. The ink is pulled through the tube by capillary force and flows onto the paper through the tip of the nib.

Why isn’t it possible to write on an extremely smooth surface with a ballpoint pen?

The tip of the ballpoint pen consists of a small ball which projects from a metallic socket. Fast-drying, oil-based ink is supplied to it through a narrow tube. When we write, the ball rotates and transfers the ink onto the paper. If the surface on which we want to write is very smooth, there will not roll efficiently. Consequently the ink will not get transferred to the paper. Sometimes, the ball may be rotating but the ink may not be able to adhere to the surface.

 

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The speed of sound in air varies. At sea level it is about 1220 kmph but at higher altitudes, where air is cooler, it slows down becoming about 1,070 kmph at a height of 11,000 metres. Because the speed of sound changes with height, planes that fly faster than the speed of sound use a Mach number to measure their speed. The Mach number is the aeroplane’s speed divided by the speed of sound at the height the aeroplane is flying.

Mach 2 indicates a speed of twice the speed of sound. At Mach 1 the plane is flying at the speed of sound. Mach 0.5 is half the speed of sound, or subsonic.

Many fighter aircraft are capable of flying at high Mach numbers.

The unit is named after Ernst Mach, an Austrian physicist.

 

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