Electricity and Magnetism

Science, Grade 6


Table Of Contents: Electricity and Magnetism

1. Introduction to Electricity

2.1. Atoms and Electric Charges
Atoms are made up of protons, neutrons and electrons. Both protons and electrons have an electric charge. Protons are positively charged and electrons are negatively charged. Neutrons are not charged particles.
2.2. Interaction of Charged Particles
The interaction of electric charges is called electricity. If particles have opposite electric charges, they attract each other. If particles have similar charges, they repel each other. These interactions explain why an atom is held together. The positively charged protons in the nucleus exert a strong attraction for the negatively charged electrons that surround the nucleus.
2.3. Electric Fields
The attraction or repulsion that exists between charged particles is known as electric force. The area around a charged particle, where an electric force is exerted, is called an electric field. For a negatively charged particle, electric force lines are drawn pointing inward toward the particle. For a positively charged particle, the lines are drawn outward. The lines on the diagram are close together right next to the particle, where the field is the strongest.
2.4. Multiple Charged Particles
When two charged particles come close together, their electric fields are combined. The top diagram represents the electric fields of particles that are attracted. The bottom diagram shows the electric fields of particles that are repelled.
2.5. The Movement of Electric Charges
Objects do not normally have a positive or negative charge. However, within the atoms of some materials, the electrons are able to leave and move to other atoms. When an object gains or loses electrons, the object can become charged. Some materials, like copper and aluminum, are called conductors because their electrons can easily move. Other materials, like plastic, are known as insulators, because their electrons will not easily move.
2.6. How Objects Become Charged
There are several ways that an object can become charged, and electrons can be transferred. Friction is the transfer of electrons between two uncharged objects that are rubbing against each other. Conduction is the transfer of charges when a charged object is in direct contact with another object. Induction is the movement of electrons within an object in response to an electric field of a charged object nearby. The electrons movement creates a charge in a certain area of the object.
2.7. Static Electricity
Static electricity occurs when electric charges build up on an object, but the electrons do not flow. Static electricity is what causes lightning. An excess of positive charges builds up on the ground while a large number of negative charges builds up in the clouds. At a certain point, the difference between the negatively charged cloud and the positively charged ground is so great that the static electricity turns into an electrical current. The bolt of lightning is actually a discharge of electrons traveling at the speed of light toward the positive charges. In the 1700s, Benjamin Franklin studied lightning and electricity. He invented the lightning rod to protect buildings during storms.
2.8. Electroscope
An electroscope is an instrument used to detect charged particles. It has a long metal rod with a knob on top and two metal leaves attached to the bottom. The leaves hang straight down if the electroscope has no charge. If a charged object touches the knob and electrons are transferred, the metal leaves become charged. Because the leaves are the same charge, they repel each other and spread apart. The leaves will move in the presence of a negative or positive charge. An electroscope can tell us if an object is charged, but it cannot tell us if the charge is negative or positive.

2. Pause and Interact

3.1. Review
Use the whiteboard text tools to complete the activity.

3. Electric Current

4.1. What is Electric Current?
The continuous flow of electric charges through a wire or similar material is called electric current. Imagine electric charges moving at a steady rate through a wire. You can count how many charges move past a given point during a certain period of time. If the charges start to flow more quickly, you would count more charges moving past the same point over the same amount of time. Therefore, the rate of flow, or the rate of the current, has increased.
4.2. Current Is Measured in Amps
The rate of flow of electrical charges, or current, is expressed in amperes, also called amps. The capital letter A is used to symbolize this unit. In equations, amps are symbolized by the capital letter I. Marie Ampere was a French physicist who lived in the early 1800s and is known for his extensive research in electromagnetism.
4.3. Two Types of Electrical Current
There are two types of electric current, DC and AC. The charges in DC, or direct current, always flow in the same direction. The charges in AC, or alternating current, flow one way and then flow the other way. They are continuously reversing direction. Many batteries produce DC electricity. You can find DC batteries in cell phones, cameras, and even cars. Electric appliances around the house such as microwaves, televisions and washing machines use AC electricity.
4.4. Direct Current vs. Alternating Current
Two famous scientists, Thomas Edison and Nikola Tesla, were both interested in developing electrical supply and power systems. Edison was a strong proponent of direct current (DC) systems while Tesla supported alternating current (AC) systems. Today, in our homes, the electrical power is supplied using alternating current because it is easier to safely control the voltage of this type of current.
4.5. Electricity in Circuits
An electric circuit is a complete path that electricity flows through. For electrical current to continuously flow, the charges must move through a path that is unbroken. This continuous flow of current within a circuit enables us to use electrical power. Our homes and machines use a variety of electric circuits.
4.6. Voltage
Electric currents will flow in a wire, as long as there is voltage. Voltage is the potential difference between two points in a circuit. Another way to think about it is the amount of energy released as a charge moves between these two points. Voltage is measured in units called volts. In equations voltage is symbolized by the letter V. The greater the voltage is, the higher the current. For example, a 1.5-volt battery used in a camera produces less electrical current than a 12-volt battery used in a car.
4.7. Electrical Resistance
An electrical current is affected by the resistance of the material it is flowing through. Resistance is measured in units called ohms, symbolized by the Greek letter omega. In equations, resistance is symbolized with an R. If the voltage remains the same, increasing the resistance will result in a decrease in the current.
4.8. Resistance Factors-Material
Factors that affect resistance include an objects material, temperature, length and thickness. Materials that are good conductors have less resistance, because their electrons are held loosely on the atoms. Materials that are good insulators have a higher resistance because their electrons are held tightly together, and electrical charges have difficulty moving.
4.9. Resistance Factors-Temperature
Some materials will increase in resistance as the temperature increases. The copper atoms within a wire move faster as they gain thermal energy. This increased molecular movement creates resistance by slowing down the flow of electric charges through the wire.
4.10. Resistance Factors-Length and Thickness
A wires length and thickness affect resistance. Longer wires produce more resistance than shorter wires. As the electrical charges move through the length of the wire, they slow down as they collide with the walls of the wire. Thinner wires are more resistant than thicker wires. Thin wires have less area for the charges to flow through, and therefore the current is slower than thick wires.
4.11. Ohms Law
Georg Ohm, a Bavarian mathematician and physicist, defined the relationship between resistance, voltage and current. The formula for this relationship, known as Ohms Law, is resistance is equal to voltage divided by the current. For example, if the voltage of a toaster is 120 volts and the current is 12 amps, then the resistance of the toaster is 10 ohms.
4.12. Electric Power
Machines and appliances transform electrical energy into other types of energy. A stove transforms electricity to heat, and a stereo transforms electricity to sound. The rate at which electrical energy is transformed into another type of energy is called electric power. The unit for electrical power is a watt, and the formula is power equals voltage times current. For example, an electric stove top that uses 240 volts and has a current of 50 amps has 12,000 watts of power.
4.13. Electricity: Measurements, Units and Symbols
This table is a summary of electric measurements, and their corresponding units, unit symbols and abbreviations in formulas. Lets look at the example of electrical power. If you are referring to the power of a light bulb, then you would use the unit called a watt. You would write 60 watts using a capital W. If you wanted to write out the formula for power, you would use the abbreviation capital P for power.

4. Pause and Interact

5.1. Review
Use the whiteboard text tools to solve the problems.
5.2. Review
Use the whiteboard text tools to solve the problems.
5.3. Review
Use the whiteboard text tools to complete the table.

5. Electric Circuits

6.1. Parts of an Electric Circuit
An electric circuit is a complete path that current flows through. All electrical circuits contain an energy source, wire and a load. The energy source causes charges to move on the path. A battery, power plant and generator are sources of energy. The wires connect the parts of a circuit. The load is a machine or device that is connected to the circuit by wires. The load transforms electrical energy to other types of energy, such as light or heat. Often a switch is included to control the current in a circuit. A closed switch allows the current to flow, while an open switch turns the current off because it causes the path to be broken.
6.2. Circuit Diagram
You can use a diagram to show the path of an electric circuit. Symbols represent each part of the circuit: the energy source, the wire, the load or resistor, and the switch. Arrows indicate the direction of the current.
6.3. Series Circuit
There are different types of circuits. The current in a series circuit can only flow in one path, and it must flow through all the circuit components. In this series circuit, the current flows through each of the bulbs in a sequence. Because all the loads in the circuit share the same current, the bulbs are the same brightness. Adding more bulbs increases the resistance. This causes a decrease in the current, which results in a decrease in the brightness of all the bulbs. If any of the bulbs fail in a series circuit, the current will stop flowing, and the other bulbs will stop working.
6.4. Parallel Circuit
The current in a parallel circuit has at least two independent paths to flow. In this parallel circuit, the current can flow through each of the bulbs without having to first flow through any of the other bulbs. If a bulb fails, the other bulbs will continue to work because the current can still flow through the rest of the circuit. The brightness of the bulbs will not change, even if others are added to the circuit. Adding loads to a parallel circuit actually decreases the overall resistance of the current because the current has more paths it can travel through.

6. Pause and Interact

7.1. Circuit
Click on the Terms button. Then click and drag each term to the correct box. Use the reset button to clear the terms and start over. Use the gear button to customize the draggable terms.

7. Batteries

8.1. Volta and the First Battery
Alessandro Volta, an Italian scientist who lived in the 1800s, developed the first battery. Volta hypothesized that a chemical reaction occurs between two metals and a salty fluid to create an electrical current. He soaked paper in salt water and placed it between zinc and silver. Then, when he connected wires to the pieces of metal, a current was produced. Volta had created the first battery, which was the foundation for modern electrochemical cells and batteries.
8.2. Electrochemical Cell
An electrochemical cell converts chemical energy into electrical energy. A cell is made up of two pieces of metal called electrodes. Often, these electrodes are made of copper and zinc. The electrodes are surrounded by a substance that conducts energy, known as an electrolyte. In this example, the electrolyte is sulfuric acid. The areas of the electrodes above the surface of the electrolyte are called terminals. A wire is connected to these terminals to make a circuit. Chemical reactions occur between the electrolyte and the electrodes, causing the electrodes to become positively and negatively charged. This difference in charges creates a voltage.
8.3. Wet Cells and Dry Cells
An electrochemical cell with a liquid electrolyte is called a wet cell. A car battery has a liquid electrolyte composed of sulfuric acid, and is an example of a wet cell. An electrochemical cell with a paste as the electrolyte is called a dry cell. A flashlight battery is an example of a dry cell.

8. Pause and Interact

9.1. Electrochemical Cell
Click on the Terms button. Then click and drag each term to the correct box. Use the reset button to clear the terms and start over. Use the gear button to customize the draggable terms.
9.2. History of Electricity
Follow the onscreen instructions.

9. Electrical Safety

10.1. Electrical Safety at Home
Safety should always be kept in mind while working with electricity. Use dry hands while using electrical appliances because water conducts electricity. Keep water away from plugs and electric cords. Standing water near electric tools can be very dangerous. Make sure your home is equipped with fuses and circuit breakers that break the electrical current if too much current starts to flow.
10.2. Lightning and Power Lines
Lightning is a powerful, yet dangerous, form of electricity. If you are caught outside in a lightning storm, stay away from power lines as well as tall trees and structures. Power lines carry high voltage electricity. If these lines are damaged or fall down during a storm, they can potentially cause serious injury. Never touch a downed electric wire.

10. Magnetism

11.1. What Is a Magnet?
A magnet is a substance that attracts the element iron or materials that contain iron. All magnets have opposite ends called the north pole and the south pole. Similar magnetic poles repel each other, and opposite poles attract each other.
11.2. Magnetic Forces, Poles and Fields
The degree to which magnets repel or attract each other depends on their magnetic forces. The greatest magnetic force is located at the poles of a magnet, but there is an area all the way around the magnet that displays magnetism. This area is called its magnetic field. In this diagram, the lines represent the magnetic force around the magnet. The closer the lines are, the greater the magnetic force. The arrows show the direction of the field.
11.3. Inside a Magnet
Inside a magnet there are clusters of atoms known as magnetic domains that are responsible for magnetic properties. If the atoms with similar magnetic fields within a domain line up in the same direction, they are said to be magnetized. Atoms that are arranged in random directions within a domain are considered to be non-magnetic. Natural elements that can be magnetic include iron, nickel, cobalt, gadolinium, samarium and neodymium.
11.4. Earths Magnetic Field
Deep in the Earth, the convection currents in the liquid iron core create a magnetic field that impacts the Earths magnetism. The Earth acts like a giant magnet, having two opposite poles and a strong magnetic field. The Earth's geographic poles are at a slightly different location than the Earths magnetic north and south poles. The positions of the magnetic poles are dynamic and they shift from year to year. This map shows the changing position of the north magnetic pole in recent history.
11.5. Electromagnetism
When an electric current flows through a coil of wire, a magnetic field is produced. This relationship between electricity and magnetism is called electromagnetism. The magnetism of an electromagnet can be controlled by switching the electric current on or off. Electromagnets are used in many devices including computers, doorbells, and cranes that pick up heavy loads.

11. Pause and Interact

12.1. Review
Use the whiteboard tools to complete the activity.

12. Vocabulary Review

13.1. Electricity and Magnetism Vocabulary Matching
Safety should always be kept in mind while working with electricity. Use dry hands while using electrical appliances because water conducts electricity. Keep water away from plugs and electric cords. Standing water near electric tools can be very dangerous. Make sure your home is equipped with fuses and circuit breakers that break the electrical current if too much current starts to flow.

13. Virtual Investigation

14.1. Circuit Building
In this investigation, you will build a variety of working circuits. You must include a switch in each circuit you build. The circuit components are provided, but you must place them in the correct configuration for the circuit to safely work. Once the circuit is working, you can measure the voltage and current at different points on the circuit. You can also explore what happens when a load (light bulb) in the circuit breaks. Click on each tab at the top for a different circuit building challenge.

14. Assessment

15.1. Electricity and Magnetism