Electric & Magnetic Energy Physical Science

Big Ideas What is electricity and in what forms does it exist? What is the relationship between electric charges, electric force, and electric power?

Atomic Structure Atoms are the basic unit of matter and have 3 parts: Positive protons and neutral neutrons in the nucleus Negative electrons that float around the nucleus in a cloud

Electricity Electricity is a form of energy that results from flowing electrons.

Conductor-electrons easily flow through these substances Copper Aluminum Platinum Gold Silver Water People Trees

Insulator-block the flow of electrons through the substance Glass Porcelain Plastic Rubber Wood

Conductors & Insulators Think of an electrical cord. The center is full of thin copper wires twisted together. These wire are good conductors because they allow the electric charge to move freely through. The outside of the cord is plastic though, so the electrical charge cannot flow through it. This design allows that cord to conduct electricity from the wall socket to the device it’s plugged into.

Current vs. Static Electricity CURRENT ELECTRICITY STATIC ELECTRICITY Electrons are controlled by moving along a path together Examples: all electric appliances Uncontrolled electrons passing from one body to another in sudden, momentary movements. Examples: clothes from the dryer or walking on carpet and touching something

Electric Charges The world is full of electrical charges, which is a property of matter that creates electric and magnetic forces. There are 2 types of electrical charges: positive and negative Like charges repel and opposite charges attract The SI unit for electric charge is Coulomb, C

Electric Force Electric charges cause objects to be attracted to each other or repelled from each other-this is called the electric force. Electric force does not require that objects touch. What happens is that each charged particle produces an electric field, or space around it where it projects its charge. Any other charged particle in that electric field will experience an electric force.

Electrical Power When an electric charge moves through an object (like a wire), it loses energy. This energy is transformed into work, such as turning a motor, and lost as heat. The rate at which electrical work is done is called electrical power.

Big Idea What relationship exists between voltage, current, and resistance?

Voltage Remember potential energy! Electric charges also have potential energy called electrical potential energy and it depends on its position in an electric field. As charges move through electric fields, they create a potential difference. This potential difference in charge is called voltage and it causes current to flow through an electrical circuit and it is measured in Volts. Voltage is the amount of work required to move a charge between 2 points.

Current A voltage causes charges to move, producing a current. Current is the rate of charge movement, or the flow of electrons through a conductor and is measured in Amperes. This is how batteries work, like a 9V battery. A voltage source, like a battery, is necessary to maintain the electrical potential energy and therefore electricity.

How batteries work… http://www.youtube.com/results?search_query=batteries%20and%20how%20they%20work&sm=3

Types of Current There are 2 types of current: Direct current (DC)-batteries, the flow of electricity is in one direction Alternating current (AC)-when you plug something into a socket, the flow of electricity moves in two directions

Batteries Electrons flow out of the - terminal and into the + terminal.

Resistance The opposition to the flow of electricity is called resistance and is measured in Ohms. Electricity will always seek the path with the least resistance (lowest Ohms). The greater the resistance, the less current there is for the given voltage. Longer wires have greater resistance than shorter wires. Thin wires have more resistance than thick wires. Conductors have less resistance than insulators.

Pipe Analogy The amount of electrical current in amps depends on voltage as well as resistance. Think of a pipe with flowing water…

Pipe Analogy The voltage is equivalent to the water pressure, the current in amps is equivalent to the flow rate, and the resistance (in Ohms) is like the pipe size. Now imagine aiming that pipe at a water wheel. The water wheel represents that energy created (in Watts).

Pipe Analogy You can increase the power generated by the water wheel in two ways. Increase the pressure of water coming out of the hose, Volts and it will hit the water wheel with more force and turn the wheel faster to make more power. You can increase the flow rate (amps) and the water wheel turns faster because of the weight of the extra water hitting it.

Relationship between V, I, and R A relationship exists between resistance, voltage, and current called Ohm’s Law. Voltage = Current x Resistance or V = IR V in volts, I in amp, R in Ω

Big Ideas How does electricity flow through open circuits? How are series and parallel similar yet different?

Circuits An electric circuit is the path that an electric current (free electrons) follows. All circuits have at least 3 parts: power source (battery), conductor (wire), and resistor (light bulb).

Circuit Diagram Symbols

Switches Some circuits have switches to control the amount of currents. Switches are used to open and close a circuit. If a circuit is open, electricity cannot flow through. If a circuit is closed, electricity can flow through.

Types of Circuits Series circuit Parallel There is only one path for the electrons to flow; if one part goes out, they all go out! There is multiple paths for electrons to flow; if one part goes out, there is an alternate path for the current to flow. This is how our homes are wired. We use fuses and circuit breakers to protect circuits from current overloads.

Series Circuit—There is only one path for the electrons to flow.

Parallel Circuit—A circuit with multiple paths for electrons to flow.

Remember that since electricity is energy, it still relates to work and power! Work = happens when force moves an object power = rate at which work is done Energy = ability to do work

Whiteboard Practice 1 Draw a series circuit with one battery, one lightbulb, and a switch.

Whiteboard Practice 2 Draw a series circuit with two batteries, two lightbulbs, and no switch.

Whiteboard Practice 3 Draw a parallel circuit with two bulbs, one battery, and no switch.

Whiteboard Practice 4 Draw a parallel circuit with three bulbs, one battery, and an open switch.

Whiteboard Practice 5 Using the circuit board at your table, build a series circuit with two bulbs, and one battery. Once it is built and both lights are on, remove one of the bulbs by unscrewing it. What happens to the other light bulb? – Record your answer on your whiteboard.

Whiteboard Practice 6 Using the circuit board at your table, build a parallel circuit with two bulbs, and one battery. Once it is built and both lights are on, remove one of the bulbs by unscrewing it. What happens to the other light bulb? – Record your answer on your whiteboard.

Whiteboard Problem 1 A light bulb with a resistance of 120  is plugged into a 160-Volt outlet. What is the current flowing through the bulb?

Whiteboard Problem 2 Find the current flowing through a 20- wire that is connected to a 12-Volt battery.

Whiteboard Problem 3 Calculate the Voltage across a 25- resistor if a 0.3-Amp current is flowing through it.

What is the current running through this circuit? Whiteboard Problem 4 What is the current running through this circuit?

Lab Time! Go to Google and type in “PHET circuit construction dc” Click on the 1st link. Click “run now” and follow the instructions on the worksheet provided.