Electricity and Magnetism

Unit 4

Electricity S8P5: Students will recognize characteristics of gravity, electricity, and magnetism as major forces acting in nature. B. Students will demonstrate the advantages and disadvantages of series and parallel circuits and how they transfer energy.

Electric Charge All matter is made up of very small

particles called atoms.What are the 2 types of charged

particles in atoms? 1. Protons- positively charged

particles 2. Electrons- negatively charged

particles

Parts of an Atom PROTONS

Each element on the Periodic Table has a different number of protons.• Protons have a

positive charge• Found within the

nucleus of the atom• Change the number

of protons change element

p

Parts of an Atom ELECTRONS

An element on the Periodic Table has the same number of electrons and protons.• Electrons have a

negative charge• Found outside the

nucleus in the electron clouds

• Change the number of electrons ionize the element (give it a charge)

e-

Parts of an Atom NEUTRONS

Most elements also have neutrons (except for Hydrogen) • Neutrons have

no charge (neutral)

• Found in the nucleus of the atom

n

The Law of Electric Charges

Law of Electric Charges: like charges repel and opposite charges attract

ChargesLike charges repel

ChargesOpposite charges attract

Electric Force and Electric Field

Electric Force: the force of attraction or repulsion on a charged particle that is due to an electric field The greater the amount of charge,

the greater the electric force. The closer the charges are, the

greater the electric force. Electric Field: the space around a

charged object in which another charged object experiences an electric force

Three Ways to Charge an Object

Friction: Charging by friction happens when electrons are “wiped” from one object onto another.

Conduction: Charging by conduction happens when electrons move from one object to another by direct contact.

Induction: Charging by induction happens when charges in an uncharged object are rearranged without direct contact with a charged object.

Electrical Potential EnergyElectrical charges can be stored

on or in objects as potential energy.

Examples:Electricity in a batteryRubbing your socks on carpetElectricity in clouds

Static Electricity Static Electricity

the accumulation of electric charges on an object that are at rest

generally produced by friction or induction

When something is static, it is not moving.

3 examples of Static Electricity Clothes from a dryer sticking together Balloon sticking to clothes after

rubbing it on your hair Negative charges on the bottom of a

cloud during a thunderstorm

Electric Discharge Electric discharge:

the release of static electricity as charges move off an object

2 examples of electric discharge: 1. Walking across

carpet and touching a metal doorknob

2. Lightning

Electrical Kinetic Energy Electricity

electrical energy due to the flow of electrons

Electric current the rate at which electric charges pass through a

given point (the rate that electrons flow)

The greater the flow of charge, the higher the current.

Electrons move from negative to positive. Electric charges will always flow from a region of

higher potential energy to a region of lower potential energy. The difference in potential energy between two

locations is known as potential difference (voltage).

Electrical ConductorsElectrical conductor:

a material in which electrons can move through easily

Electrons (e-) are loosely held

Examples: Most metals (copper, aluminum, and mercury)

Electrical Insulators

Electrical insulator a material in which electrons are not

able to move easily Electrons (e-) are tightly held Examples: Plastic, rubber, glass, wood,

and air

DC and AC 2 types of electric

currents: DC: direct current AC: alternating

current In a direct current, the

charges always flow in the same direction (one way). Ex. Dry cell battery

In an alternating current, the charges continually shift from flowing in one direction to the reverse direction at regular intervals (two ways). Ex. Electrical outlets

Voltage Voltage

the push or force that causes electrons to move from negative to positive

a measure of how much work is needed to move a charge between two points

• The size of the current depends on the voltage.

• The greater the voltage, the greater the current.

• A greater current means that more charges move in the wire each second.

Resistance Resistance

a measure of how difficult it is for electrons to move through a material

electrical energy is converted to thermal energy and light (Ex.: a light bulb)

You can think of resistance as “electrical friction.”

A resistor is an object that is added to a circuit that restricts the flow of electrical energy.

An object’s resistance depends on its material, thickness, length, and temperature.

Good conductors, such as copper, have a low resistance. However, poor conductors, such as Tungsten, have a higher resistance.

Copper - low resistance

Tungsten - high resistance

Cells Batteries are chemical cells. Batteries convert chemical

energy into electricity. A battery can provide the

voltage (push) that is needed to keep current flowing in a circuit.

• Electric charges are repelled by the negative terminal and attracted toward the positive terminal.

Photocells are devices that convert light energy into electrical energy. Ex. Solar panels

Electric Circuits:Parts of an Electric Circuit

What is a circuit?-a complete, closed path through which electric charges flow

Just like a roller coaster, an electric circuit forms a loop; it begins and ends in the same place.

All circuits need 3 basic parts. 1. Energy source- provides energy to the circuit; can be a battery,

a photocell, or an electric generator at a power plant

2. Wires- connect the other parts of a circuit; made of conducting materials that have low resistance, such as copper

3. Loads- change electrical energy into other forms of energy; examples include light bulbs, appliances, televisions, and electric motors

A Switch to Control a Circuit A switch is used to open and close a circuit. In order for loads (like the lights in this classroom) to work, the

switch needs to be closed to allow charges to flow through. If a switch is open, the load will not work.

Types of Circuits

What are the 2 types of circuits? Series circuits Parallel circuits

Series Circuit Series Circuit:

a circuit in which all the parts are connected in a single loop only one (single) path for charges to follow; so, the charges

moving through this circuit must flow through each part of the circuit.

Series Circuits: Advantages and Disadvantages

Advantages: The bulbs and batteries will last longer. Use less power The current is the same throughout the circuit; therefore,

lights shine with equal brightness. Disadvantages

Lights get dimmer as more lights are added.• Each device (light bulb, etc.) receives a fraction of the

total voltage.• Adding more bulbs resistance goes up, current goes

down, and bulbs get dimmer Only one path for charges to flow.

• A break in a series circuit causes charges to stop flowing; if one light in a series circuit goes out, the other lights go out, too.

Parallel Circuit Parallel circuit – a circuit that has more than

one path for the flow of electricity because the parts are joined in branches or multiple loops

Parallel Circuits: Advantages and Disadvantages Advantages:

The voltage (potential difference) across each part is the same.• Each bulb will glow at full brightness

regardless of the number of bulbs. There are multiple paths for charges to

travel.• If one bulb breaks, the other bulbs will

still work. Disadvantages:

The bulbs and batteries will die faster. Use more power The current is not the same in the

circuits• current takes path of least resistance

Household Circuits

Combination of parallel circuits too many devices

can cause wires to overheat

Safety Features: fuse - metal

melts, breaking the circuit

circuit breaker - bimetallic strip bends when hot, breaking the circuit

Magnetism and Electromagnetism

S8P5. Students will recognize characteristics of gravity, electricity, and magnetism as major kinds of forces acting in nature.

c. Investigate and explain that electric currents and magnets can exert force on each other.

Magnetism

Magnetism

The properties and interactions of magnets

Due to the arrangement of electrons

Closely related to electricity

Magnetic ForceMagnetic Force

Force of attraction or repulsion generated by moving or spinning electric charges

Increases as magnets move closer together and decreases as magnets move farther apart

Magnetic Poles Magnetic Poles

Regions on a magnet where the magnetic force exerted by a magnet is the strongest

Like poles repel.

Opposite poles attract.

A broken magnet creates new poles.

Magnetic FieldMagnetic Field

Area around a magnet where magnetic forces act

Magnetic field lines show the direction of the field (NS)

Molecular Expressions: Electricity and Magnetism - Interactive Java Tutorials: Magnetic Field Lines

Earth’s Magnetic Field Earth’s inner core is

made of a solid ball of iron and nickel surrounded by a liquid layer of molten iron and nickel.

The circulation of the molten iron and nickel in the Earth’s outer core produces a magnetic field.

Therefore, Earth acts like a giant bar magnet.

Compass

A compass needle is a small bar magnet with a north pole and a south pole.

The needle aligns with the magnetic field lines of the Earth.

Earth’s Magnetic Poles A compass’

needle points to the north geographic pole due to the south magnetic pole being nearby. Magnetic poles

are NOT aligned with geographic poles. They also shift and flip.

Magnetic Domains Magnetic Domains

Groups of atoms with aligned magnetic poles Like tiny magnets of different sizes

In a magnetized object, the domains are all aligned.

domain

In a non-magnetized object, the domains are not aligned and cancel each other out.

Magnetic MaterialsFew metals such as iron, cobalt,

and nickel are attracted to magnets or can be made into permanent magnets.

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Types of MagnetsFerromagnets: magnets

made of iron, nickel, cobalt, or mixtures of these metals (ex. magnetite)

Electromagnets: magnets formed when current passes through a coil of wire (solenoid) surrounding an iron core

Permanent MagnetsPermanent Magnets

Magnets that keep their magnetism after they are removed from a magnetic field

Keep their magnetic properties longer than temporary magnets

Some are made of alnico: an alloy of aluminum, nickel, cobalt, and iron.

Permanent MagnetsPermanent magnets can be

made:Place a magnetic material (iron,

cobalt, or nickel) in a strong magnetic field.

This causes the magnetic domains in the material to line up.

This creates a strong magnetic field inside the material which keeps the domains in alignment.

Can be heated or dropped to demagnetize

Temporary MagnetsTemporary Magnets

Magnets made from materials that are easy to magnetize

Tend to lose their magnetism easily

Ex. Soft iron items like paperclips and nails

Magnetism in Nature Auroras

They are formed when charged particles from the sun (known as solar wind) hit oxygen and nitrogen atoms in the air. The atoms become excited and then give off many colors of light.

The charged particles can crash into the atmosphere at and near the magnetic poles.• North Pole

Northern lights: aurora borealis

• South Pole Southern lights: aurora

australis

aurora borealis

aurora australis

Magnetism and Electricity Moving charges,

like those in an electric current, produce magnetic fields.

Around a current-carrying wire the magnetic field lines form circles.

Magnetism and Electricity As the current in

the wire increases, the strength of the magnetic field increases.

The direction of the magnetic field around the wire reverses when the direction of the current in the wire reverses.

Electromagnetism

ElectromagnetismThe interaction between

electricity and magnetism

SolenoidsSolenoid

A single wire wrapped into a cylindrical wire coil that produces a magnetic field when electricity passes through it.

If wrapped around an iron core, an electromagnet is formed.

ElectromagnetsElectromagnet

A magnet formed when current passes through a coil of wire (solenoid) surrounding an iron core

The iron core becomes magnetized only when current flows through the wire.

ElectromagnetsThe strength of an electromagnet’s

magnetic field can be increased by:Adding more wraps of wire to the

solenoid Increasing the current passing

through the wire by increasing the voltage.

Increasing the size of the iron core

Properties of an Electromagnet

Has a north and a south pole If placed in a magnetic field, it will

align itself along the magnetic field lines

Will attract magnetic materials and be attracted or repelled by other magnets

Useful because the magnetic properties can be controlled by changing the electric current

Electric MotorsElectric Motors

Devices that convert electrical energy into mechanical energy

An electromagnet rotates between the poles of a permanent magnet.

Electric Motor Animation

Electromagnetic Induction

Electromagnetic Induction The process in which

an electric current is produced in a wire by changing a magnetic field

Michael Faraday (1831), a British scientist, discovered this process.

An electric current can be produced by moving a magnet through a coil of wire

Electric GeneratorsElectric Generators

Devices that use electromagnetic induction to convert mechanical energy into electrical energy

As the crank is turned, the rotating coil crosses the magnetic field lines of the magnet, inducing a current in the wire.

MOTORGENERATOR

Electric Generator Animation

Electric Generators After the wire coil makes one-half of a revolution,

the ends of the coil are moving past the opposite poles of the permanent magnet. This causes the current to change direction:

• Alternating Current (AC)

Electric Generators

Examples: Power plants use

generators which have many coils of wire wrapped around huge iron cores. The rotating magnets are connected to turbines which are large wheels that rotate when pushed by water, wind, or steam. • Nuclear power plants

use thermal energy from a nuclear reaction to boil water into steam in order to turn the turbines.

• Wind mills are connected to generators.

Alternators in vehicles Gasoline generators

Electric Generators Example

Hydroelectric Dam

The Potential Energy (PE) of lake water is converted to Kinetic Energy (KE).

Mechanical KE turns the generator shaft which generates electrical energy.