ELECTRICITY - STATIC ELECTRICITY - #11

Static Electricity

Static electricity is the build up of an electrical charge on the surface of an object. It's called "static" because the charges remain in one area for a while rather than moving or "flowing" to another area. 
We see static electricity every day. It can even build up on us. For example, when we rub our feet on the carpet and then zap something when we touch it. That is static electricity that we have built up on the surface of our skin discharging onto another object. We also see it when our hair gets charged and sticks straight up or when our pant legs keep sticking to our legs no matter what we try and do. This is all static electricity that has built up on the surface of an object. 

Lightning is a powerful form of static electricity

What is static electricity? 
In the study of atoms we learned that atoms are made up of neutrons, protons, and electrons. The electrons are spinning around the outside. A static charge is formed when two surfaces touch each other and the electrons move from one object to another. One object will have a positive charge and the other a negative charge. Rubbing the items quickly, like when you rub a balloon fast over something or your feet on the carpet, will build up a large charge. Items with different charges (positive and negative) will attract, while items with similar charges (positive and positive) will push away from each other. Sort of like a magnet. 

Remember when you've gone down a slide and all your hair stands up straight. This is because the friction of sliding has caused a positive charge to be built up on each hair. Since each hair has the same charge, they all try to push away from each other and end up standing up straight. 
Likewise, when your skin is charged with static electricity and you touch something metal, like a door handle, the metal is very conductive and will quickly discharge the static electricity, creating a zap or small spark. 
Does it have any real uses? 
Static electricity has several uses, also called applications, in the real world. One main use is in printers and photocopiers where static electric charges attract the ink, or toner, to the paper. Other uses include paint sprayers, air filters, and dust removal. 

It can damage electronics 
Static electricity can also cause damage. Some electronic chips, like the kind that are in computers, are very sensitive to static electricity. There are special bags to store these in. Also, people that work with these kind of electronics wear special straps that keep them "grounded" so they won't build up charge and ruin the electronic components. 
Fun facts about static electricity
A spark of static electricity can measure thousands of volts, but has very little current and lasts for a short period of time. This means it has little power or energy.

• Lighting is a powerful and dangerous example of static electricity.
• As dangerous as lighting is, around 70% of people struck by lightning survive.
• Temperatures in a lightning bolt can hit 50,000 degrees F.
• Static electricity will be worse on a dry non-humid day.

ELECTRICITY: DC POWER #10

A Direct Current

There are two main types of current in our world. One is direct current (DC) which is a constant stream of charges in one direction. The other is alternating current (AC) that is a stream of charges that reverses direction. Let's look at DC power which was refined by Thomas Edison in the 1800s.

Moving in One Direction

The current in DC circuits is moving in a constant direction. The amount of current can change, but it will always flow from one point to another. Before we move on, we need to explain that physicists, as well as electricians, refer to something called conventional current.

Do you remember that we talked about physicists agreeing to always use positive charges to determine how electric field lines would be drawn? Following through on that agreement, they also agreed to explain charge flow in terms of positive charges rather than electrons. So although electrons would flow from negative to positive, by convention (agreement), physicists refer to conventional current as a flow from high potential/voltage (positive) to low potential/voltage (negative). Reminding you that potential is like electrical height, this means that conventional current flows "downhill", which makes sense.

Electrons move from areas where there are excess of negative charges to areas where there are a deficiency (or positive charge). Electrons move from "-" to "+", but conventional current is considered to move in the other direction. When you set up a circuit, conventional current is considered to move from the "+" to the "-" side.

The idea about using positive charges in forming explanations comes from Benjamin Franklin. In Franklin's day, we didn't know about protons and electrons. Franklin  believed that something moved through electrical wires, and he called these things "charge". He assumed there was only one kind of charge, and he logically assumed that charge would flow from a spot that had an excess (extra), to a spot that had a deficiency (too few). He called the spot with an excess "positive" and the spot with a deficiency "negative". So, for Franklin, charge flowed from positive to negative. We simply honor his achievements by continuing with this idea.

Battery Basics

The best real-life example of direct current is a battery. Batteries have positive (+) and negative (-) terminals. If you take a wire and connect the positive and negative terminals on a battery, the electrons in the wires will begin to flow to produce a current. You can prove that the current is flowing if you connect a small light to the circuit. The light will begin to glow as the electrons pass through the filaments. 

DC power is used all over the world. You will probably use direct current power whenever you carry something around that uses electricity. Everything that uses batteries runs on DC power. Other countries use more portable power supplies because they might not have electric wiring in their houses.

That electric wiring in your house is AC power and it is completely different than DC. There are machines that can convert DC to AC power. Those machines might be used to take a DC battery in a boat and convert the power to AC so that a refrigerator can use it.

ELECTRICITY - MAGNETISM & MAGNETS #9

Magnetism

Domain Theory of Magnetism

Magnets are made of iron, nickel or cobalt. In a magnet, there are groups of atoms called domains, each of which behaves like a tiny magnet.
In demagnetised steel, the domains point in different directions and cancel one another out. In magnetised steel, the domains are pulled about until they point in the same direction, thus reinforcing each other.

Demagnetised

Magnetised

• Properties of Magnets

1. There are 2 ends or poles of the magnet (north and south)
2. The north pole of a suspended magnet points north. The south pole of a suspended magnet points south.
3. Unlike poles attract each other (e.g. north and south). Like poles repel each other (e.g. north and north, south and south).
   
   
    
4. Magnets attract objects made of iron.
5. Repulsion between a magnet and another object indicates that the other object is also a magnet.
6. A magnet that is dropped or heated may lose its magnetism due to non-aligned or 'scrambled' domains.
7. A magnetic field is the region around a magnet where lines of magnetic force point from north pole to south pole.

Magnetic Field of a Bar Magnet

• 4 Ways to Make a Magnet

1. Stroke the magnetic material (e.g. screwdriver or metal ruler) with a bar magnet in the same direction
2. Hold the magnetic material near a bar magnet for a long period of time
3. Hold the magnetic material in a north-south direction, and strike it 30 or more times with a hammer
4. Make an electromagnet by winding some plastic-coated wire around the magnetic material and connecting the wire to a battery

COMPLETE HAND-OUT MAGNETISM - 

What is a Magnet?

A magnet is an object or a device that gives off an external magnetic field. Basically, it applies a force over a distance on other magnets, electrical currents, beams of charge, circuits, or magnetic materials. Magnetism can even be caused by electrical currents.

While you might think of metal magnets such as the ones you use in class, there are many different types of magnetic materials. Iron (Fe) is an easy material to use. Other elements such as neodymium (Nd) and samarium (Sm) are also used in magnets. Neodymium magnets are some of the strongest on Earth.

Different Types of Magnets

There are many different types of magnets. Permanent magnets never lose their magnetism. There are materials in the world that are called ferromagnetic. Those materials are able to create and hold a specific alignment of their atoms. Since many atoms have a magnetic moment (tiny magnetic field), all of the moments can add up to create a magnet. Scientists use the word hysteresis to describe the way the atoms stay aligned.

Most of the magnets you see around you are man-made. Since they weren't originally magnetic, they lose their magnetic characteristics over time. Dropping them, for example, weakens their magnetism; as does heating them, or hammering on them, etc.

There are also air-core magnets. Air-core magnets are created by current flowing through a wire. That current produces the magnetic field. You create an air-core magnet by wrapping miles of wire around in a doughnut shape (toroid). When you send current through the wire, a magnetic field is created inside of the doughnut. Scientists sometimes use air-core magnets to study fusion reactions.

Electromagnets are different because they have a ferromagnetic material (usually iron or steel) located inside of the coils of wire. The core isn't air, it is something that aids in producing magnetic effects, so electromagnets are typically stronger than a comparable air-core magnet. Air-core and electromagnets can be turned on and off. They both depend on currents of electricity to give them magnetic characteristics. Not only can they be turned on and off, but they can also be made much stronger than ordinary magnets. You might see an electromagnet at work in a junkyard lifting old cars off the ground.

REVIEW:

Magnetism is an invisible force or field caused by the unique properties of certain materials. In most objects, electrons spin in different, random directions. This causes them to cancel each other out over time. However, magnets are different. In magnets the molecules are uniquely arranged so that their electrons spin in the same direction. This arrangement of atoms creates two poles in a magnet, a North-seeking pole and a South-seeking pole. 

Magnets Have Magnetic Fields 

The magnetic force in a magnet flows from the North pole to the South pole. This creates a magnetic field around a magnet. 

Have you ever held two magnets close to each other? They don't act like most objects. If you try to push the South poles together, they repel each other. Two North poles also repel each other. 

Turn one magnet around, and the North (N) and the South (S) poles are attracted to each other. Just like protons and electrons - opposites attract. 

Where do we get magnets? 

Only a few materials have the right type of structures to allow the electrons to line up just right to create a magnet. The main material we use in magnets today is iron. Steel has a lot of iron in it, so steel can be used as well. 

The Earth is a giant magnet 

At the center of the Earth spins the Earth's core. The core is made up of mostly iron. The outer portion of the core is liquid iron that spins and makes the earth into a giant magnet. This is where we get the names for the north and south poles. These poles are actually the positive and negative poles of the Earth's giant magnet. This is very useful to us here on Earth as it lets us use magnets in compasses to find our way and make sure we are heading in the right direction. It's also useful to animals such as birds and whales who use the Earth's magnetic field to find the right direction when migrating. Perhaps the most important feature of the Earth's magnetic field is that it protects us from the Sun's solar wind and radiation. 

The Electric Magnet and Motor 
Magnets can also be created by using electricity. By wrapping a wire around an iron bar and running current through the wire, very strong magnets can be created. This is called electromagnetism. The magnetic field created by electromagnets can be used in a variety of applications. One of the most important is the electric motor. 

 

MAGNETS - VIDEO

ELECTRICITY: COULOMB'S LAW #8

Coulomb Basics

Coulomb's Law is one of the basic ideas of electricity in physics. The law looks at the forces created between two charged objects. As distance increases, the forces and electric fields decrease. This simple idea was converted into a relatively simple formula. The force between the objects can be positive or negative depending on whether the objects are attracted to each other or repelled.

Think about a few concepts before you continue reading. Some charges are attracted to each other. Positive and negative charges like to move towards each other. Similar charges such as two positive or two negative push away from each other. You also need to understand that forces between objects become stronger as they move together and weaker as they move apart. You could yell at someone from far away, and they would barely hear you. If you yelled the same amount when you were together, it would be more powerful and loud.

Coulomb's Work

Charles Augustin de Coulomb was a French scientist working in the late 1700's. A little earlier, a British scientist named Henry Cavendish came up with similar ideas. Coulomb received most of the credit for the work on electric forces because Cavendish did not publish all of his work. The world never knew about Cavendish's work until decades after he died.

Coulomb's Law

But you're here to learn about the law. When you have two charged particles, an electric force is created. If you have larger charges, the forces will be larger. If you use those two ideas, and add the fact that charges can attract and repel each other you will understand Coulomb's Law. It's a formula that measures the electrical forces between two objects.

F=kq₁q₂/r²

"F" is the resulting force between the two charges. The distance between the two charges is "r." The "r" actually stands for "radius of separation" but you just need to know it is a distance. The "q1" and "q2" are values for the amount of charge in each of the particles. Scientists use Coulombs as units to measure charge. The constant of the equation is "k." As you learn more physics, you will see that this formula is very similar to a formula from Newton's work with gravity. 

REVIEW:
 Coulomb's Law

• The interaction between charged objects is a non-contact force that acts over some distance of separation. Charge, charge and distance. 

• Every electrical interaction involves a force that highlights the importance of these three variables.
•  Whether it is a plastic golf tube attracting paper bits, two like-charged balloons repelling or a charged Styrofoam plate interacting with electrons in a piece of aluminum,
• there is always two charges and a distance between them as the three critical variables that influence the strength of the interaction.

ELECTRICITY: RESISTANCE #7

Resisting Current

The collisions between electrons and atoms in a conductor cause resistance to the flow of charge. We measure that resistance in order to determine the effect that it will have on current. Scientists measure resistance in ohms (rhymes with homes). There is a magical little formula used to figure out the resistance in an electrical system. That formula is called Ohm's Law, V=IR.

Measuring Resistance

The symbol "V" is used to represent something called the potential difference. Potential difference is the amount of work done in moving a charge between two points, divided by the size of the charge. That's kind of complicated, though. You can think of potential as electrical height. High potential (near positive charge) is kind of like being on top of a hill. Low potential (near negative charge) is kind of like being in a valley. So potential difference indicates the difference in electrical height between two points. The greater that difference, the more likely it is that charge will move. The potential difference is measured in volts, and potential is commonly referred to as voltage. "I" is the  symbol for current and "R" is the symbol for the resistance of the system. Current is measured in amperes and resistance is measured in ohms.

How can you think of resistance? Have you ever gone to a baseball game? Between innings, we like going to get some food. There are always people between the counter and us. Resistance to current is similar to you trying to make your way through the crowds to get your hot dog. You have to weave your way through the people to reach your goal. The more people in your way, the more resistance. If everyone is in their seats it is super-easy to get your food. There would be very little resistance.

Let's go back to that equation and look at it in terms of resistance. When you move the values around you get R=V/I. In English that means the resistance of a system is based on voltage and current. Not all conductors follow Ohm's law.

Resistance is also based on the resistivity of a material. The resistivity of a material changes because of chemical makeup or the temperature. 

• Copper is a better conductor than wood so copper would have lower resistivity. That resistivity combines with (1) the distance and (2) the space that charges have to move in (thin vs. thick wires) to affect the "R" value. Greater length results in more resistance, and thick wires result in less. When people connect speakers, they usually use wires that are as short and thick as possible. 

Knocking Electrons Around

In metals, electrons carry the charges of the current as it flows. What stops the electrons? What offers the resistance to that current? Nothing allows a perfect flow of current, not even superconductors. In metal, there are tiny flaws. You can't see them because they are on a molecular level. Those imperfections cause the electrons to collide with the metal atoms. When they hit the metal, the electrons lose energy. Where does that energy go? It is usually turned into heat. You can watch a hot plate heat up, or maybe a stove top. They heat up because of the collisions between electrons and the metal. Imperfections mean collisions; collisions mean heat.

ELECTRICITY: CONDUCTORS #6

Flowing Electrons

Electric current is very similar to a flowing river. The river flows from one spot to another and the speed it moves is the speed of the current. The size of the current flow is related more to the size of the river than it is to the speed of the river. A river carries more water each second than a stream, even if both flow at the same speed. With electricity, current is a measure of the amount of charge transferred over a period of time. Current is a flow of electrons, or individual negative charges. When charge flows, it carries energy that can be used to do work. Scientists measure current with units called amperes. 

Current and Heat
One of the results of current is the heating of the conductor. When an electric stove heats up, it's because of the flow of current. The electrons have a mass (however small), and when they move through the conductor, there are collisions that produce heat. The more electrons bumping into the atoms of the conductor, the more heat is created, so higher current generally means greater heat.

Scientists used to think that the flow of current always heated up the object, but with modern superconductors, that is not always true, or at least not as true as with normal materials. Superconducting materials seem to have less interaction between atoms and current, so the moving charges lose much less energy.

Spaces Between Atoms

Everything that is matter can conduct electricity, but not everything does it well. Scientists use the terms conductors, insulators, and semi-conductors. The labels are used to describe how easily energy is transferred through the object by moving charge. The spaces between the atoms, as well as the type of atoms, determines whether an object a good conductor or a good insulator (poor conductor).

Usable Current

There are two main kinds of electric current, direct current (DC) and alternating current (AC). They are easy to remember. Direct current is a flow of charge always in one direction. Alternating current is a flow of charge back and forth, changing its direction many times in one second. Batteries produce DC current, while the outlets in our homes use AC current.

Be very careful if you work with electricity. NEVER touch the plugs in your house. That electricity is very powerful and it can hurt you… badly. Electricity from batteries can also injure you. We have burned ourselves when working with batteries and electromagnets, so we know what can happen. To be safe, go get an adult to help you with any experiments.

ELECTRICITY: MAGNET FIELDS #5

Magnetic Field Basics

Magnetic fields are different from electric fields. Although both types of fields are interconnected, they do different things. The idea of magnetic field lines and magnetic fields was first examined by Michael Faraday and later by James Clerk Maxwell. Both of these English scientists made great discoveries in the field of electromagnetism.

Magnetic fields are areas where an object exhibits a magnetic influence. The fields affect neighboring objects along things called magnetic field lines. A magnetic object can attract or push away another magnetic object. You also need to remember that magnetic forces are NOT related to gravity. The amount of gravity is based on an object's mass, while magnetic strength is based on the material that the object is made of.

If you place an object in a magnetic field, it will be affected, and the effect will happen along field lines. Many classroom experiments watch small pieces of iron (Fe) line up around magnets along the field lines. Magnetic poles are the points where the magnetic field lines begin and end. Field lines converge or come together at the poles. You have probably heard of the poles of the Earth. Those poles are places where our planets field lines come together. We call those poles north and south because that's where they're located on Earth. All magnetic objects have field lines and poles. It can be as small as an atom or as large as a star.

Attracted and Repulsed

You know about charged particles. There are positive and negative charges. You also know that positive charges are attracted to negative charges. A French scientist named Andre-Marie Ampere studied the relationship between electricity and magnetism. He discovered that magnetic fields are produced by moving charges (current). And moving charges are affected by magnets. Stationary charges, on the other hand, do not produce magnetic fields, and are not affected by magnets. Two wires, with current flowing, when placed next to each other, may attract or repel like two magnets. It all has to do with moving charges.

Earth's Magnetic Field

Magnets are simple examples of natural magnetic fields. But guess what? The Earth has a huge magnetic field. Because the core of our planet is filled with molten iron (Fe), there is a large field that protects the Earth from space radiation and particles such as the solar wind. When you look at tiny magnets, they are working in a similar way. The magnet has a field around it.

As noted earlier, current in wires produces a magnetic effect. You can increase the strength of that magnetic field by increasing the current through the wire. We can use this principle to make artificial, adjustable magnets called electromagnets, by making coils of wire, and then passing current through the coils.