What Happens If You're Struck By LIGHTNING?

What Happens If You're Struck By LIGHTNING? | Thunder & Lightning 

 

Light and optics

 

Light and optics

Light is the kind of energy that makes it possible for us to see. Without light there would be no life on earth. Green plants use the sun’s light to grow and produce food. In this process they produce oxygen, which we need to breathe. Without plants there would be no animals or food.

Light also provides us with fuel. The energy that the sun has sent to earth for millions of years has been stored in plants and then changed into coal, oil and gas – energy that we use today to operate machines and produce electricity and power.

We also get heat from the sun. Without it our planet would be so cold that nothing could live on it. 

Sources of light

All light comes from atoms, tiny particles that make up everything in our universe. When atoms gain energy they give it off as light. An atom that has such energy is called excited.

Some light is natural , like sunlight or light from stars . Other light is produced from things people make, like lamps or flashlights. A light bulb glows because electricity heats a wire inside. Candles produce light from fire when you light them. Lasers are devices that produce powerful beams of light in which all particles have the same energy and travel in the same direction.

There are certain substances that glow in the dark. Their atoms are excited for a certain time and after that they release light. Some insects, like fireflies glow naturally.

Nature of light

For a long time scientists were not sure about how light travels through space. Some thought that light behaves like a wave, others claimed that light particles travel in a straight line. Today, scientists agree that light is an electromagnetic wave made up of electrical and magnetic forces that travel through space at a very high speed. However, light is also a stream of particles called photons, which travel like a beam.

Light waves can be compared to waves in water. They have a wavelength, frequency and amplitude. The wavelength is the distance between the two highest parts of a wave, the frequency is the number of times that a wave passes a certain point every second, and the amplitude is the distance between the highest and lowest points of a wave. 

Electromagnetic waves

Not all electromagnetic waves are visible. Light refers to those waves that we can see.

Light that comes from the sun is basically white. It is made up of all colours. When it passes through a specially shaped glass called a prism it breaks up into different colours. When the sun comes out while it is still raining, we often observe a rainbow because light must pass through raindrops. It breaks up into all the colours of the visible spectrum. Violet light is at one end of the spectrum because it has the shortest wavelength, red light, which has the longest wavelength, is at the other end.

Ultraviolet rays are invisible waves with shorter wavelengths. They cause sunburn and may lead to skin cancer. In small amounts these rays have a good effect on our skin because they produce vitamin D. X rays are even shorter rays that can penetrate a human body. Doctors use them to take pictures of bones and other inside organs.

Waves with lengths longer than red light are called infrared rays. When you stand in front of a fire you feel warm, largely because infrared light is shining on you. Microwaves and radio waves are even longer. Microwaves are used to make food warm. Radio and TV stations broadcast programs by sending out radio waves, which may have a wavelength of up to a few meters.

How light behaves

When light waves strike an object three things may happen. The light can be reflected, absorbed or it may change its direction.

What happens to light depends on the kind of object or material that it hits. Transparent objects, like glass, let light waves pass through without mixing them up. You can see through this material. Translucent material also allows rays to pass through, but it mixes them up so that you cannot see through such objects clearly. Opaque materials don’t let any light pass through. 

Reflection

Most objects do not produce their own light. You can see these objects because light from the sun or from a lamp bounces off them and then travels to your eyes.

Some objects reflect little light, others, like mirrors or water reflect almost all the light because they are smooth and flat. The rays bounce off in only one direction. Reflected light also makes things sparkle and shine. When light shines on a normal object, like a tree, the rays bounce off in many directions.

 

Refraction

When light passes through an object it slows down because the molecules of a solid object are more densely packed than air molecules. It also changes its direction of travel – it refracts.

Example: Swimming pools do not look as deep as they really are because of the way light is bent. Water slows light down by about 25 per cent and glass slows it down even more. Light waves bend towards the glass, slow down and behind the glass resume their normal speed.

Another example is picking up a stone in water. The stone is not where you think it is. It appears to be farther away than it really is.

Scattering

Scattering shows us what happens when light rays hit atoms, molecules or tiny particles. These particles send off light in new and different directions. Most of the sky is blue because air molecules scatter more blue rays towards us than they do the other colours in sunlight. When the sun reaches the horizon in the evening it looks orange or red because the light that gets to us has lost so many of the other colours through scattering.

Colour

The colour of an object depends on the way it reflects and absorbs light. An object can absorb certain colours and reflect others. The colour that we see is a combination of all the colours it reflects, we can’t see the colours that it absorbs. An apple, for example, looks red because its surface reflects colours from the red end of the spectrum and absorbs the rest.

White objects reflect all colours of light, black objects absorb all colours.

How light is measured

Speed of light

Light travels fastest in empty space, where nothing can block its path. Its speed here is always the same: about 300,000 km per second. The light from the sun, which is about 150 million km away from the earth, reaches our planet in about 9 minutes.

Brightness

The brightness of light is measured in the unit candles, a name that dates back to the old days when wax candles were the only ways of lighting up a room. The amount of light that an object receives depends on how far away the light source is. If a simple candle shines directly on a flat surface that is one foot (about 30 cm) away light has an intensity of one foot-candle. An average 60 watt light bulb emits about 60 foot candles of light. In the metric system we measure the intensity of light in the unit lux. 1 lux is the light that shines on a flat surface one metre away.

Wavelength and frequencies

Scientists measure wavelengths in nanometres, which equals one billionth of a metre. Visible light ranges from 400 nanometres for violet light to about 700 nanometres for red light.

Frequencies are measured in a unit called hertz. A wave has a frequency of one hertz if one crest of the wave passes a checkpoint every second. Because visible light has a short wavelength and a high speed it has a high frequency, Violet light for example has a frequency of 750 trillion hertz. Radio waves, on the other hand have very low frequencies.

Electricity

 

Electricity

Everything is made up of atoms. Each one of them has three particles : protons, neutrons and electrons. Electrons spin around the centre of an atom. They have a negative charge. Protons, which are in the centre of atoms, have a positive charge.

Normally, an atom has as many protons as it has electrons. It is stable or balanced. Carbon, for example has six protons and six electrons.

Scientists can make electrons travel from one atom to another. An atom that loses electrons is positively charged, an atom that gets more electrons is negatively charged.

Electricity is created when electrons move between atoms. Positive atoms look for free negative electrons and attract them, so that they can be balanced.

Conductors and Insulators

Electricity can pass through some objects better than through others. Conductors are materials through which electrons can travel more freely. Copper, aluminium, steel and other metals are good conductors. So are some liquids like saltwater.

Insulators are materials in which electrons cannot move around. They stay in place. Glass, rubber, plastic or dry wood are good insulators. They are important for your safety, because without them, you couldn’t touch a hot pan or plug in a TV set.

Electric Current

When electrons move through a conductor an electric current is created. A current that always flows in one direction is called a direct current (DC). A battery for example, produces a direct current. A current that flows back and forth is called an alternating current (AC).

Electric Circuits

Electrons cannot jump freely through the air to a positively charged atom. They need a circuit to move. When a source of energy, like a battery, is connected to a light bulb the electrons can move from the battery to the light bulb and back again. We call this an electric circuit.

Sometimes there are many circuits in an electrical device that make it work. A TV set or a computer may have millions of parts that are connected to each other in different ways.

You can stop the current from flowing by putting a switch into the circuit. You can open the circuit and stop electrons from moving.

A piece of metal or wire can also be used to produce heat. When an electrical current passes through such metal it can be slowed down by resistance. This causes friction and makes the wires hot. That’s why you can toast your bread in a toaster or dry your hair with warm air from a hairdryer.

In some cases wires can become too hot if too many electrons flow through them. Special switches ,called fuses, protect the wiring in many buildings . 

Kinds of electricity

Static electricity

·         happens when there is a build-up of electrons

·         it stays in one place and then jumps to an object

·         it does not need a closed circuit to flow

·         it is the kind of electricity you feel when you rub your pullover against an object or when you drag your feet over a carpet.

·         lightning is a form of static electricity

Current electricity

·         happens when electrons flow freely between objects

·         it needs a conductor—something in which it can flow , like a wire.

·         current electricity needs a closed circuit

·         it is in many electrical appliances in our homes - toasters, TV sets , computers.

·         a battery is a form of current electricity

 How batteries work

A battery has liquid or paste in it that helps it produce electric charges. The flat end of the battery has a negative charge and the end with the bump has a positive charge.

When you link a wire between both ends a current flows. When the current passes through a light bulb electric energy is converted into light.

The chemicals in the battery keep the ends charged and the battery going. As times passes, the chemical becomes weaker and weaker and the battery cannot produce any more energy.

 How electricity is produced

Generators are used to transform mechanical energy into electrical energy. A magnet rotates inside a coil of wire. When the magnet moves, an electric current is produced in the wire.

Most power stations use turbines to make the generator rotate. Water is heated to make steam , which pushes the blades of the turbine. Gas, oil or coal can be used to heat the water. Some countries build power stations on rivers, where the moving water pushes the turbine blades.

 How electricity is measured

Electricity is measured in watts, named after James Watt who invented the steam engine. It would take about 750 watts to equal one horsepower.

A kilowatt-hour is the energy of 1,000 watts that work for one hour. If, for example, you use a 100-watt light bulb for 10 hours you have used 1 kilowatt of electricity.

 How electricity is transported

The electricity produced by a generator travels along cables to a transformer that changes the voltage of electricity. Power lines carry the high-voltage electricity over very long distances. When it reaches your home town another transformer lowers the voltage and smaller power lines bring it to homes, offices and factories.

 Electrical safety

 It is important to understand why and how you can protect yourself from electrical injuries.

Electric shock occurs when an electric current passes through your body. It can lead to heart failure and can damage other parts of your body. It can also burn your skin and other body tissues.

A very weak electrical object, like a battery, cannot do any harm to you, but inside the house you have devices and machines that use 220 volts.

Most machines in your house have safety features to protect you. It something goes wrong, a special wire leads the electricity to the ground where nothing can happen.

There are also electrical dangers outside your house. Trees that touch power lines can be dangerous. Lightning has more than enough electricity to kill a person. If you get caught in a thunderstorm stay away from open fields and high places. One of the safest places is your car, because lightning will only hit the outside metal of the car.