electricity and magnetism circuits electromagnets chapter 17 and 18

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Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

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Page 1: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Electricity and MagnetismCircuitsElectromagnetsChapter 17 and 18

Page 2: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

How can you produce electricity?...right now!

Page 3: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

The Law of Electric Charge

Like charges repel – push away

Opposites attract

Page 4: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Electric Field

A region around a charged object in which an electric force is exerted on another charged object.

How do we create charge?

Page 5: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Friction electrons are “wiped” from one object to

another

Page 6: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Conduction Conduction – electrons move through

direct contact (a shock!)

Page 7: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Induction• when charges are rearranged without

direct contact

Page 8: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Circuits

Series

Each part of the circuit is in a series or in one loop.

Parallel You will have more

than one loop. You should be able

to unscrew one bulb and the other stays lit.

Never connect more than one wire to each side of the battery!

Page 9: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

What Is Static Electricity?

A stationary electrical charge that is built up on the surface of a material

Page 10: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18
Page 11: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Static Discharge Human body can not feel less than 2,000 volts of static discharge

Static charge built up by scuffing shoes on a carpet can exceed 20,000 volts.

Page 12: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

What is an electric circuit? A complete loop

(begins and ends at the same place) through which electric charges flow.

Page 13: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

The Essential Parts of a Circuit1. An energy source – battery etc.2. Wires – to carry the electric charge3. Load – light bulb, radio etc.

Page 14: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Types of CircuitsThe parts of a circuit can be connected in different ways. The two main types are:1. Series2. Parallel

Page 15: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Series Circuits All parts are connected in a single loop

All loads in a series circuit share the same current

Page 16: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Parallel Circuit A circuit in which loads are connected

side by side Current in a parallel circuit has more

than one path Each load receives the full amount of

energy the energy source can provide (voltage) and they will use as much current as they need Ex. 45 vs. 60 Watt light bulb

Page 17: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Switches Some circuits in include a switch to

open and close the circuit (turn it on and off) Open – off (the loop is broken) Closed – on (the loop is closed or

complete)

Page 18: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Series Circuit Will all bulbs burn

with the same brightness? Yes, all receiving the

same electric current. What will happen if

I add a bulb? They will all dim b/c

they will receive less electric current.

What happens if one bulb burns out? They will all go out,

the loop is no longer complete.

Page 19: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Parallel Circuits Will all bulbs burn

with the same brightness? No, it depends on their

wattage. What will happen if

I add a bulb? They will continue to

burn with the same brightness.

What happens if one bulb burns out? The remaining bulbs

will stay lit.

Page 20: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Questions to Consider: Which circuit would be more useful in lighting

a home or building? Parallel, you want to be able to have the lights

on in one room and off in another. Which circuit is used in Christmas tree lights?

It depends, they used to be made in series, if one burned out all went out. Nowadays many are made in parallel so the remaining bulbs will continue to burn.

Why are series circuits useful? Burglar alarms

What drawbacks are there in using parallel circuits?

Page 21: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Voltage The unit of measure for potential difference is the

Volt (V)Think 9 volt battery

The device that provides the potential difference is considered the voltage source;

Page 22: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

How does the flow begin? Electrons in a circuit have potential

energy The potential energy of each charge is

called electrical potential In a battery, the electrical potential of one

terminal is higher than the other terminal The difference in this potential energy is

called potential difference This potential difference causes the loose

electrons to be pulled away from their atoms and flow through the material

Page 23: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Current The current is the rate at which a charge

passes a given point The unit for current is the ampere or

Amp (symbol - A) An amp is the amount of current that

flows past a point in one second

Page 24: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

ResistanceThe opposition to the flow of

charges in a circuit.Measured in ohms - Ώ

Page 25: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Ohms law, Defines the relationship between voltage, current and resistance.

Page 26: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18
Page 27: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18
Page 28: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18
Page 29: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

EXPLORING MAGNETISM

Page 30: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

What Do Magnets Do?

Attract or repel other magnets (exert a force)

Attract other magnetic metals

Have at least 2 distinct ends (poles) each

Page 31: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Magnetic Field

This is the area in which a magnetic force can be exerted.

Magnetic force is stronger the closer you are to the magnet.

Page 32: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Magnetic Force

Like poles repel, opposite poles attract

Page 33: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Magnetic Materials

What makes some things magnetic, while other things can’t be magnetized?

Spinning electrons cause small magnetic fields around each atom.

Magnetic materials have atoms whose magnetic fields can be lined up in the same direction.

Areas where atoms’ magnetic fields line up are called magnetic domains.

magnetic domain

Randomly arranged domains = No magnet!

Magnetic domains lined up = Magnet!

Page 34: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Permanent MagnetsA permanent magnet is a material that keeps its magnetic properties even when it is NOT close to other magnets.

Page 35: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Electricity to Magnetism

In 1820, H.C. Oersted discovered that an electric current flowing through a wire had a magnetic field around it.

Electricity can cause magnetism! Electromagnets are powerful magnets that can be turned

on and off.

You can make an electromagnet stronger by (1) putting more turns of wire in the coil or (2) making a larger soft iron core, or (3) increasing the current through the wire.

Page 36: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

What is a solenoid?Electricity and magnetism are closely

related. This was first seen when a solenoid was developed.

A solenoid is simply a coil of wire that when current is flowing through it will generate a magnetic field.

Page 37: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Electromagnet:

A stronger version of the solenoid!It creates a temporary magnet when a current-

carrying wire coil surrounds a magnetic metal core. Useful because they can be turned off Adding and removing coils can increase or decrease

strength

Page 38: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Moving a loop of wire through a magnetic field produces an electric current. This is electromagnetic induction.

A generator is used to convert mechanical energy into electrical energy by electromagnetic induction.

Electromagnet Induction

Page 39: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Electromagnetic Devices

39

Generators: convert mechanical energy into electrical using an electromagnet

Electric Motors: use electrical energy through electromagnet to create mechanical energy (i.e. to turn an axle)

Page 40: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

What are electric motors?An electric motor is a device which changes electrical energy into mechanical energy.

Page 41: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

What is a generator?

Page 42: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Uses for electromagnets A simple DC electric motor

contains a permanent magnet, an electromagnet, and a commutator. When current flows through the electromagnet, it turns within the magnetic field of the permanent magnet, changing electricity to mechanical energy.

Current meters also use permanent magnets and electromagnets. When current flows through a wire, it makes an electromagnet. The force between the electromagnet and the permanent magnet makes a needle move on the meter.

Page 43: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Magnetism to Electricity

Joseph Henry and Michael Faraday discovered that magnetism could also produce electric current. This is called electromagnetic induction.

If a magnet is moved back and forth through a coil of wire, current can be made to flow through the wire. This is the idea behind electric generators and transformers.

Current moves left in wire. Current moves right in wire.

Page 44: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Uses for Electromagnetic Induction Generators produce AC

current for home and industrial use. Water, wind, or steam are used to move large electromagnets through the coils of wire to produce current.

Transformers are used to step up voltage of electricity that must travel long distances through wires. Other transformers then step down the voltage before it enters our homes.

Page 45: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Direct Current

If the voltage is maintained between two points in a circuit, charge will flow in one direction - from high to low potential. This is called direct current (DC)

Battery-powered circuits are dc circuits.

Page 46: Electricity and Magnetism Circuits Electromagnets Chapter 17 and 18

Alternating Current

If the high & low voltage terminals switch locations periodically, the current will flow “back and forth” in the circuit. This is called alternating current (AC).

Circuits powered by electrical outlets are AC circuits.