What is Electromagnetic Spectrum?

Electromagnetic radiation is made from two sorts of energy— electrical and magnetic. As the radiation moves outward from its source, its energy constantly changes from strong to weak and back again. The changing energy sets up a pattern that scientists call waves.

What is wavelength?

Scientists can measure the distance between two points where the magnetic energy or the electrical energy is strongest. This distance is called the wavelength of the electromagnetic radiation and is usually measured in meters or fractions of meters.

What is frequency? 

Count how often a ball bounces against a wall and back in one minute. You are measuring how often, or how frequently, the ball bounces during a certain time. Scientists measure electromagnetic radiation by counting the number of times magnetic energy and electric energy change from strong to weak. The number of complete changes in one second is called the frequency. We measure frequency in units called hertz, or Hz.

Scientists draw pictures like this to help us understand electromagnetic radiation, such as radio waves. The red waves show how the strength of the magnetic field changes as a radio wave travels.
The frequency of the red waves is lower than the frequency of the blue waves. This is because the wavelength of the red waves is longer.

The electromagnetic spectrum

Electromagnetic radiation travels out in every direction from the point, or source, where it is generated. This radiation travels out at an enormous speed—186,282 miles (299,792 kilometers) per second in a vacuum. In other words, electromagnetic radiation would take more than one second to reach the moon, which is about 239,000 miles (384,473 kilometers) away from the earth.
The frequency of electromagnetic radiation can be as low as a few hertz. Or it may be as high as thousands of billions of hertz. Scientists call the whole range of different frequencies the electromagnetic spectrum.
At one end of the electromagnetic spectrum are gamma rays, which have the highest frequencies. At the other end of the spectrum are radio waves, which have the lowest frequencies. In between are X rays, ultraviolet waves, visible light, infrared radiation and microwaves.
Scientists have developed appliances that use electromagnetic radiation to help us in our daily life. These appliances include X-ray machines, cameras, microwave ovens, television and radios.
X rays have very high energy and so pass easily through many different materials. X rays are used to make X-ray photographs of the bones inside our bodies.

How does a metal detector work?

Have you ever hunted for buried treasure? 

You could just start digging anywhere and hope that you would find something. 

Or you could use a metal detector to find out exactly where metal objects are buried under the ground. 

Magnetism makes a metal detector work. Do you know how?

The kind of metal detector that treasure hunters use is made up of a flat coil of wire fixed to one end of a short pole. At the other end is a handle, and a box containing a battery and electronic circuits.
As the treasure hunter moves the coil above the ground, the battery produces an electric current that sends out a magnetic field from the coil.
This field makes any buried metal object, such as a coin, send back its own magnetic field. When the metal detector receives the coin's field, a light flashes on the handle of the pole.

The magnetic field around the moving coil creates electric currents in any metal object, such as a coin, that is buried in the ground.
These currents create a magnetic field around the buried object.
The metal detector's electronic circuits detect the magnetic field made by the currents.
A light on the handle of the pole flashes to tell the treasure hunter that the detector has found a metal object.

Can you think of any other uses for a metal detector? 

There are metal detectors in vending machines to test whether the coins put in the slot are real or fake.
There are metal detectors at airports so that security guards can make sure no one takes dangerous weapons, such as guns, onto airplanes.
Metal detectors under the road control some sets of traffic lights, where a major road crosses a minor road. The lights will change to 'Go' for the minor road only when a car comes along. Magnetism makes all these different kinds of metal detectors work.

What is a Solenoid and What can Solenoids Do? - Experiments for kids

Part of an electromagnet is called a solenoid. 

A solenoid is a coil of wire that has an electric current flowing through it. When an electric current flows through a wire, the electricity creates a magnetic field around the wire.
If the wire is wound into a coil, the magnetic field around the coil becomes much stronger.
We can make the magnetic field even stronger by putting a rod of iron or steel into the solenoid. 
The magnetic field becomes stronger because the metal rod is magnetized by the solenoid.
Like a bar magnet, a solenoid has two poles.
The flux lines of the magnetic field link together the north and south poles of the solenoid.

How does a solenoid magnetize an iron rod? 

The iron rod is made up of lots of groups of atoms called domains. These domains are miniature magnets, but their magnetism has no power because their poles are pointing in different directions.
When an iron rod comes into a magnetic field around a solenoid, the domains in the rod all line up and point one way.
Then the rod has strong magnetic poles at each end and a magnetic field around it.
When an electric current runs through a solenoid, it has poles just like a bar magnet.
One end is a north pole and the other end is a south pole.
If you hold an iron or steel rod near a solenoid, the rod becomes magnetized, and the end of the rod that's nearest the north pole of the solenoid becomes a south pole.
In the same way, the end of a rod held near the south pole of the solenoid will become a north pole.
Unlike poles attract, and so the magnetized rod and the solenoid attract each other.

Electromagnet experiment for kids - What can Solenoids do?

You can make a solenoid and see for yourself how a steel rod moves inside the coil when the electric current flows.

1. Cut a piece of the drinking straw about 1 inch {2.5 centimeters) long. 

Wind the wire many times around the short piece of straw to make a solenoid. 

Always wind the wire in the same direction. 

Leave about 10 inches (25 centimeters) of wire free at each end.

2. Connect one end of the solenoid wire to one terminal of the battery.

3. Stand the pin upright on the table. With the other hand, place the solenoid over the pin. Hold the solenoid upright with the pin inside it.

4. Hold the free wire from the solenoid against the free battery terminal and the electric current will flow. 

Don't touch the bare end of the wire! 

As the current flows, the pin jumps up into the coil. 

It will stay there until the current is switched off.

5. Now switch the connections to the battery. 

Does the pin still jump up into the solenoid? 

Does it matter in which direction the electric current flows through the coil?

Solenoids at work

Solenoids can pull iron rods towards them.
Can you think of ways in which a solenoid can be useful?
Solenoids can work as a kind of switch in electric door locks, in pinball machines, and in electric circuit breakers.

When you press down a switch on an electric door lock, an electric current flows through a solenoid and creates a magnetic field around it. When the current flows, the metal rod in the lock becomes magnetized and is pulled into the coil. This action pulls the bolt back and the door is unlocked.

Solenoids and magnets

If we use a solenoid with a magnet, instead of an ordinary iron rod, the solenoid can not only pull the magnet towards the coil, but also push it away.
So the magnet moves both backwards and forwards.

1. When an electric current flows through the coil, the rod becomes magnetized. It is pulled inside the coil.

2. The electric current is now reversed and it flows in the opposite direction. The rod is again magnetized and pulled inside the coil.

3. The rod is now replaced by a bar magnet. 

When an electric current flows through the coil, the bar magnet is pulled inside the coil.

4. What happens when the electric current is reversed?  The coil pushes the magnet away. When the current flows in a different direction, the magnet moves in a different direction.

Inside a loudspeaker

Loudspeakers can turn electric signals into sounds that we can hear. Inside a loudspeaker there is a solenoid attached to a thin cone. The solenoid is also attached to a powerful permanent magnet. Wires connect the solenoid to a sound system or a television. Electric signals pass through these wires and through the solenoid. The signals are vibrations carried by an electric current.

The solenoid moves backwards and forwards as the electric signals vibrate at different speeds, up to 40,000 times a second. This makes the cone vibrate. The vibration of the cone makes the sounds we hear.

How to make an electromagnet?

An ordinary bar magnet has a magnetic field around it all the time. We call this kind of magnet a permanent magnet. You can also make a magnet by wrapping wire around an iron rod or bolt. When an electric current passes through the wire, the rod works like a magnet. We call this kind of magnet an electromagnet. We use electromagnets in many household appliances, such as refrigerators and vacuum cleaners.

How to make a electromagnet?

1. Line up the compass needle so that it points to the north. Place it near one end of the ruler, with the ruler facing east- west.
2. Now make an electromagnet by winding the 20-inch (50-centimeter) wire many times around the bolt. Always wind the wire in the same direction. Leave about 4 inches (10 centimeters) of wire free at each end. Place the electromagnet facing east-west on the ruler near the compass

3. Connect the electromagnet to the "D" battery and watch the compass needle. It should swing towards the electromagnet. If it doesn't, move the electromagnet closer to the compass.
Where does the electromagnet have to be on the ruler to make the compass needle point halfway between the N and the W? Mark this point on the ruler.

4. Now make a second electromagnet with the longer wire, leaving about 6 inches (20 centimeters) of wire free at each end. Disconnect the first electromagnet. Place the second one on the ruler at the mark you made earlier, and connect it to the "D" battery.

What happens to the compass needle?
Does it swing around farther than before?
Remember, twice as much wire means twice as much resistance. This makes the current half as strong.

How to make an electromagnet stronger?

What can you learn from the experiment on this page?
The strength of an ordinary bar magnet is permanent and fixed.
But we can make the magnetism around an electromagnet weaker or stronger, and we can even turn it off completely.
How can you make an electromagnet stronger? 
How did you increase the magnetism in the electromagnet?

The electromagnet has become stronger because the 6-volt battery is sending more electric current through it.
More electric current makes an electromagnet stronger.
The needle moves farther than before.

When was the Compass Invented?

The first explorers had very little to help them find their way around the world. Travelers used simple maps and learned how to find their way, or navigate, using the sun and the stars.
During the day, travelers can always find out where east and west are, because the sun rises in the east and sets in the west. At night, they can use the stars to find out where north and south are.
An imaginary line called the equator circles the world halfway between the North and South poles.
In countries north of the equator, the North Star shows which way is north.
A pattern of bright stars called the Big Dipper points to Polaris, the North Star.
In countries south of the equator, the upright line in a group of stars called the Southern Cross points to the south.

When was the Compass Invented?

In the 11th century, a Chinese scientist called Shen Kua made a magnetic compass. 
He held up a thread of silk attached to the center of a needle and watched the needle point to the south. When he rubbed the needle with a loadstone, it pointed to the north.
About 100 years later, sailors began to use magnetic compasses to find their way across the oceans.
Three or four hundred years ago, most ships carried a piece of loadstone that sailors used to magnetize their compass needles. Loadstone, also spelled lodestone, is a hard black magnetic rock.
A long piece of this rock would point north / south if hung by a string.

Modern compasses

Hikers and sailors still use magnetic compasses to tell directions. Small boats made of wood or fiberglass use a magnetic compass called a mariner's or maritime compass. It consists of a ring-shaped magnet attached to a card. The points of the compass are marked on the card.
The card and magnet float in a bowl of water mixed with alcohol. The compass always floats horizontally, so that it can work properly even in stormy seas.
Magnetic compasses don't work properly near steel or electrical machines. So modern ships use a special compass called a gyrocompass.
Gyrocompasses do not use magnetism and can be set to point towards the geographic North Pole.

How to Make a Magnet - Magnets for Kids

How to Make a Magnet?

If you have one magnet already, you can magnetize another piece of metal, such as a steel needle, to make a new magnet.

This is how to do it. 
Hold a steel needle in one hand and a bar magnet in the other hand.
Stroke one end, or pole, of the magnet all along the needle several times.
You must always use the same pole of the magnet, and stroke the needle in the same direction.
In between strokes, lift the magnet in a curve high above the needle from one end to the other.

You have now magnetized the needle.


It's easy to make a steel needle into a magnet. Stroke the needle several times with one end of a bar magnet. Make sure you always stroke in the same direction. 
Always use the same end of the bar magnet.

Magnet composition - What's inside a magnet?

How does the needle become magnetized? 

Actually, there were magnets inside the needle even before you stroked it with the magnet.
The needle, the magnet, and everything in the world are made up of tiny building blocks called atoms.
Atoms are so small that even if you could put a million atoms side by side, a strand of human hair would be thicker.
The atoms in a steel needle group together into domains, which are magnetized bunches of atoms.
Inside a magnet, all the domains point in the same direction and create a magnetic field around the magnet.
But in the steel needle, the domains point in all different directions.
There is no magnetic field around the needle because the domains cancel each other out.
When you stroke a steel needle with a magnet, you make all the domains line up in the same direction. Then the needle becomes a magnet, too.

What happens if a bar magnet is cut in half ? 

There will be two magnets!
Do you know why?
When the magnet is cut in half, the domains are still lined up in each piece. So each half becomes a magnet, with a north pole at one end and a south pole at the other end. If each magnet is cut in half again, there will be four magnets.

Earth Magnetic Field - What is Earth Magnetic Field?

We live on a huge magnet! 
Around the earth is a giant magnetic field, just like the magnetic field around a bar magnet.

Do you know what makes the earth magnetic? 

Very deep inside the earth, there's hot molten metal.
The earth is always spinning around very fast, and scientists think this causes electric currents in the molten metal.
These electric currents might create the magnetic field around the earth.

Although the earth is round, it has magnetic poles at two ends just like a bar magnet.
Imagine a rod passing through the middle of the earth from north to south.
One end is the north magnetic pole, and the other end is the south magnetic pole.
But the magnetic poles are not in the same places as the North Pole and the South Pole on a geographer's map.
These geographic poles are at true north and true south, which are where the earth's lines of longitude meet. But compasses point to the north and south magnetic poles, which are points in the earth's magnetic field.
The north magnetic pole is in Canada, about 870 miles (1,400 kilometers) from the geographic North Pole. The south magnetic pole is in Antarctica, about 1,710 miles (2,750 kilometers) from the geographic South Pole.

Using the earth magnetism

We use magnetism to send radio signals across long distances.
The earth magnetism helps to trap a layer of electrical particles around the planet. This layer is called the ionosphere. Radio signals can be sent from the ground to bounce off the ionosphere and return to the ground a great distance from where they started.
Sometimes electrically charged particles burst out from dark patches on the sun, called sunspots.
A stream of these particles, called the solar wind, sweeps past the earth. The solar wind interferes with the ionosphere. When this happens, compass needles swing wildly in all directions, and we can't send radio signals across long distances.

Aurora Borealis and Aurora Australis

Beautifully colored lights can sometimes be seen in the night sky near the North and South poles. These lights are called the aurora.
The aurora borealis in the north and the aurora australis in the south appear when particles from the sun hit the top layer of the earth's atmosphere. Some of these particles are trapped by the earth's magnetic field and move toward the planet's magnetic poles.

The beautiful northern lights, called aurora borealis, shimmer in the night sky near the North Pole. The lights appear when electrical particles from the sun hit the earth's atmosphere.

What is a Magnetic Field - Magnetic Field definition for kids

You can't see magnetism, but you can feel it working near a magnet.

In the space around a magnet is a magnetic field. 

If you hold something made from magnetic material, such as iron or steel, in a magnetic field, you can feel the magnet and the metal attract each other even before they touch.
If you hold the north pole of one magnet near the north pole of another magnet, you can feel the two magnets repel each other.

The shape of a magnetic field changes when you put two magnets together.
If you put the north pole of one bar magnet near the south pole of another bar magnet, you can think of their magnetic field as consisting of imaginary lines, called flux lines, that pass from one magnet to the other. Between the centers of the poles, the flux lines are straight.
Moving away from the centers, the lines curve in ever-expanding arches.
If you put the north poles of two bar magnets close together, there are no flux lines because the magnets repel each other.
There's a huge magnetic field around the sun. Glowing gases burst out from the sun's surface. These gases help us to see the curved shapes of the sun's magnetic field.
When two magnets are end to end, the shape of the magnetic field around them depends on which poles are facing each other. The lines show how the magnets either attract or repel each other.

What is Magnetism - Magnetism for kids

We use magnetism in so many ways that modern life would be impossible without it.
We need magnetism to produce large amounts of electricity in power stations.
There are magnets in compasses, loudspeakers, electric motors, refrigerator doors, computer disks, and many other useful appliances.
Magnetism is an invisible force that can make some things move towards each other, or move away from each other, or stay in one place.
We can't actually see magnetism, but we can look at magnets and see what happens to certain things that are put near them.
The area around a magnet is called a magnetic field.
When magnets and some metals are inside a magnetic field, magnetism makes them move.
A strong enough magnet can make steel paper clips jump off a table. This is caused by an invisible force, called magnetism, which surrounds every kind of magnet.

What are magnets made of?

When a magnet is surrounded by a magnetic field all the time, we call it a permanent magnet. Most permanent magnets are made from steel or from mixtures, called alloys, of iron and other metals.
Many magnets are made from an alloy called Alnico. This contains the metals aluminum, nickel, iron and cobalt. The bold letters show you how we form the name Alnico.
Permanent magnets are made of metal and can make other metals move toward them.
Scientists describe metals that magnets can attract in this way as magnetic. Iron, steel, cobalt and nickel are magnetic.
But not all metals are magnetic.
For example, magnets do not attract aluminum or copper. Scientists describe these metals as nonmagnetic.
You can find out for yourself whether something is magnetic or nonmagnetic.
Hold a small magnet near a piece of paper to see if the paper will move towards the magnet. Now try the same experiment with things made of plastic, glass and cloth.
Are these materials magnetic or nonmagnetic?
Iron filings stick to the ends of a magnet where the magnetic force is strongest.
These ends are called the poles of the magnet.

What shape is a magnet?

Magnets are made in several shapes, including bars, horseshoes, rings, disks, and cylinders.
Magnetism works in a different way around each shape of magnet.
We use bar magnets in compasses, horseshoe magnets in small electric motors, and disk magnets in radio, television, or stereo.

Magnetic Poles - North and south poles

Magnetism is strongest at the ends, or poles, of a bar magnet.
Scientists call one end of a bar magnet the north-seeking pole because it always tries to point towards the north.
The other end is called the south-seeking pole.
We call them the north pole and south pole for short.
Do you want to know which end of your bar magnet is the north pole? 
You can find out which direction is north with a compass.
Hang the magnet from a piece of string so that it can swing freely. When it eventually stops swinging, the end of the magnet that points north is the north pole of the magnet.

If you put a metal object made of iron, steel, cobalt or nickel near a magnet, the magnet will pull the metal toward it. 

Scientists say that the magnet attracts the metal. 

Magnets can also attract other magnets, but sometimes magnets push away from each other. 

Then scientists say that the magnets repel each other.

Like and unlike poles

To make a triangle of magnets, each north pole must be next to a south pole. If you try to put two like poles together, the triangle will fall apart.
You can feel two magnets attract each other if you hold the north pole of one magnet near the south pole of another magnet. But if you put two poles of the same kind close together, two north poles or two south poles, then the magnets will repel each other. Scientists have a rule to help us remember this. The rule is, "Like poles repel, unlike poles attract."

See this for yourself by making a triangle with three bar magnets.
You can't make the magnets stay together if you put two like poles next to each other.
The north pole of one magnet, for example, will always repel the north pole of another magnet.
If you want your magnets to attract each other and stay close together, the north pole of one magnet must be next to the south pole of the other magnet.