Download Unit 8: Electricity and Magnetism

Unit 8: Electricity and Magnetism
Notes
Chapter 4: Electricity and Magnetism
Lesson 1: What is Static Electricity
Two Kinds of Change
 An electric charge is a basic property of the tiny particles that make up matter
 Electric charge can be either positive or negative
 Positive and negative charges cancel out each other
 Neutral is when you have a balance of positive and negative charges
 Negatively charged- has more particles with a negative charge
 Positively charged- has more particles with a positive charge
 Opposite charges attract- pull toward each other
 Same charges repel- push away from each other
 Static electricity is the buildup of charges in one place
o Ex. When clothes crackle and stick together after taking them out of the
dryer
Separating Charges
 Negative charges can be moved by rubbing an object against another (positive
charges CANNOT be moved)
 Two ways to separate charges:
o rubbing objects together
o bringing a charged object near a neutral object
Electric Forces
 An electric force is the push or pull between objects that have different charges
 Positive and Negative electric charges have electric fields, the space in which an
electric force acts, around them
 As you move farther from a charged object, the force gets weaker
 The field of a positive charge attracts a nearby negative charge or repels a positive
charge (refer to the diagram on pg. 182-183)
Lesson 2: What Makes a Circuit
Moving Charges
 In static electricity, an object becomes charged when it gains or loses negative
charges
 The charge jumps only if it has a path- like from the carpet to you, or from you to
the doorknob
 In electric current, the charges have a path to follow, they flow, or move (a
steady flow of charges)

An electric circuit is a closed path that electric current follows. (the battery and
the light bulb)
Series Circuits
 A series circuit has only one path for its current to follow
 In a series circuit the current flows from the battery (power source), through the
wires, passes through each device (light bulb), and flows back to the battery
(closed circuit)
 The same amount of current flows to each device
 Removing any device causes all devices to stop working (open circuit)
Parallel Circuits
 A parallel circuit has more than one path for current to flow
 It’s more convenient to use than the series circuit because even if the charge is
blocked on one path it still has another path to follow
 In parallel circuits, the current is split between the paths
 Parallel circuits allow people to use devices separately. (light switches in our
homes)
Resistance
 The amount of current that can flow through a circuit depends on its resistance
 Resistance is how much a material opposes the flow of current
 The greater the resistance, the less current can pass through a circuit
 Examples of high resistance would be a light bulb- as the current passes through
the filament, it resists the flow causing it to get hot- then glow from the heat
 High resistance is used to produce heat and light
 Examples-toasters, space heaters, light bulbs
 In a short circuit, current flows where it isn’t wanted- they prevent the rest of the
circuit from working properly
Lesson 3: Conductors and Insulators
Conductors
 A conductor is a type of material through which negative charges can move
easily.
 Metals are good conductors because they allow negative charges to move through
them easily
 Negative charges are “pushed” through a conductor
 Examples of conductors are copper and silver
Insulators
 An insulator is a material that resists the flow of electricity
 Examples of insulators are cardboard, foam, rubber, or plastic
Lesson 4: What Makes an Electromagnet
Making a Magnetic Field
 A magnet that has coils of current-carrying wire around an iron core is called an
electromagnet.
 An electromagnet is a temporary magnet
 It only has a magnetic force only when an electric current passes through the wire
 When there is not current, the electromagnet doesn’t work
Controlling Electromagnets
 Electromagnets can be controlled by turning them on and off
 They can also be controlled by switching the connections to the battery- which
switches the magnetic field (the N field becomes the S field)
 They can be made stronger by:
o Using more coils
o Increase the strength of the electric current (add more batteries)
Need to Know
Unit 8: Electricity and Magnetism
 All definitions
 Characteristics of conductors (allow electricity to flow) and
insulators (do not allow electricity to flow)
 Examples of conductors (metals, salt water etc…) and
insulators (plastic, wood, etc…)
 Be able to draw and label a circuit
 Be able to describe how a circuit works
 Know the difference between a series and a parallel circuit
 Know what an electromagnet is and how it works
 Be able to draw and describe an electromagnet
 Why objects attract (opposite charges) and repel (alike
charges)