Electricity and Magnetism Introduction/Review
Overall Expectations By the end of this unit, students will: 1. Analyse the social, economic, and environmental impact of electrical energy production and technologies related to electromagnetism, and propose ways to improve the sustainability of electrical energy production; 2. To investigate, in qualitative and quantitative terms, magnetic fields and electric circuits, and solve related problems; 3. Demonstrate an understanding of the properties of magnetic fields, the principles of current and electron flow, and the operation of selected technologies that use these properties and principles to produce and transmit electrical energy
Big Ideas Concepts that students should retain long after this course are: Relationships between electricity and magnetism are predictable Electricity and magnetism have many technological applications Technological applications that involve electromagnetism and energy transformations can affect society and the environment in positive and negative ways
Getting started; Useful Concepts & Skills Concepts review: 1. a) What are the four main parts of any electric circuit? b) What are their functions?
2. a) What are ammeters and voltmeters used for? b) Indicate, on the diagram below, how an ammeter and a voltmeter should be connected?
3. The diagrams below show two types of electric circuits. What are they called? How can you tell?
4. What are the properties of (i) electric current and (ii) electric potential difference in (a) a series circuit and (b) a parallel circuit?
5. There is something wrong with each circuit below. Identify the problem and suggest a way to solve it.
6. Draw a circuit that contains a battery connected in series with a motor followed by two lamps connected in parallel with each other. Include switches to control each lamp independently. a) what would happen if both switches were closed? b) what would happen if both switches were open? c) what would happen if one switch was closed?
Introduction to Electricity What is Electricity? The flow of electrons (copy) Law of Electric Charges 1) opposite charges attract each other 2) Like charges repel each other 3) Charged objects attract some neutral objects Electric Charge Transfer The transfer of charge from one object to another is caused by a large difference in the number of unbalanced electrons in the two objects
(copy) Conductor vs. Insulator Conductor material that readily allows the transfer of electrons (i.e. copper, aluminum, steel, etc.) Insulator material that resists the flow/transfer of electrons (i.e. rubber, air, etc.)
copy Charging by Friction, Contact and Induction Friction Contact Induction -Electrons are stripped away by one material from another (one material has a greater attraction) -Eg. Rabbit fur and ebonite rod -When two objects come in contact, their charge will balance -Eg. A positive rod and a negative pith ball -The process of forcing electrons out - objects do not touch - charged object is brought close and then grounded -Eg. A positive rod and an electroscope
Current, Potential Difference, and Resistance (copy) Concept Definition Symbol Unit Formula Measured? Current The rate of electron flow I Amperes (A) I = Q/t Using an ammeter connected in series Potential Difference Resistance
The Direction of Electric Current Activity on pg. 503 building an LED circuit Activity on pg. 518 how much current can a lemon produce?
The Direction of Electric Current Electron Flow Negatively charged electrons move from the terminal through the circuit to the + terminal of the source
Electric Current Electric current comes in two forms; direct current and alternating current In direct current (DC), the current flows in one direction only and doesn t increase or decrease in magnitude Direct current is produced by an electric cell, such as a battery, to power portable electrical devices
(copy) Concept Definition Symbol Unit Formula Measured? Current Potential Difference The rate of electron flow Direct Current (DC) current flows in one direction (batteries, solar cells) I Amperes (A) I = Q/t Using an ammeter connected in series Resistance
Electric Current In alternating current (AC), the current moves back and forth, alternating direction Alternating current is produced by generators at electric generating stations Alternating current is used because it is a more efficient method of distributing electrical energy over long distances Wall outlets provide alternating current
( copy) Concept Definition Symbol Unit Formula Measured? Current The rate of electron flow Direct Current (DC) current flows in one direction (batteries, solar cells) I Amperes (A) I = Q/t Using an ammeter connected in series Potential Alternating Current (AC) current moves back and forth, more efficient for long distances (wall outlets, generators)
Did you know? The nerve cells in your body communicate with each other by creating very small electric currents If a larger current is transmitted through your body it can overload your nervous system By touching a wire with a current flowing through it, you can affect the current in your body Muscles will contract and you may not be able to let go of the wire The electric current will also cause burns, because some of the electrical energy will be transformed into thermal energy **sometimes a current of 0.016 A is referred to as the letgo threshold because if the current is above this value, the person cannot let go of the object giving the electric shock
copy electron flow Direct Current (DC) current flows in one direction (batteries, solar cells) (A) ammeter connected in series Potential Difference The change in electric potential energy associated with charges at two different points in a circuit V Volts (V) V = E Q Using a voltmeter connect in parallel Resistance The measure of a materials natural opposition to the flow of electrons R Ohms (Ω) V = IR
Did you know? An important part of the body s nervous system is the neuron, a nerve cell which can receive, interpret, or transmit electrical messages An electric potential difference exists across the surface of every neuron because of a greater number of negative charges on the inside than on the outside The potential difference is typically about 60 mv to 90 mv
Force at a Distance Electrical Fields Like charges repel As you get further away, the charge gets weaker With like charges, field lines interact, repel Example of a force at a distance.no contact required