Chapter 15. Electricity and Magnetism

Transcription

1 Chapter 15 Electricity and Magnetism

2 History of Electrostatics Electrostatics is the study of the nature, behavior, and uses of static electricity. Benjamin Franklin is famous for his study of electricity!

3 The Study of Static Electricity The Electric Charge: We know that all matter consists of tiny particles called atoms which contain protons, neutrons, and electrons. Protons and electrons have a certain amount of electric charge. This electric charge enables them to attract and repel each other.

4 The Study of Static Electricity The Electric Charge cont Protons are positive (+) Electrons are negative (-) Electricity is the result of the transfer of electrons.

5 The Study of Static Electricity Ordinarily the charges are in equal balance and the atom is said to be neutral. If an atom loses an electron or gains an electron, it is charged.. Too many electrons? It is negatively charged. Too many protons? It is positively charged.

6 The Study of Static Electricity Opposite charges neutralize each other!!! One of the ways to cause an atom to gain or lose electrons is with friction. When an objects rub against each other, the electrons can rub off one object onto another.

7 The Study of Static Electricity Whenever charges are built up in two objects by friction, one object is charged negatively and the other is charged positively.

8 Electric Fields We cannot see electric fields we CAN map them with imaginary lines. These lines are called lines of Force

9 Measuring Charge The more electrons an object gains or loses, the stronger its charge will be. The unit of charge is the coulomb One coulomb equals 6.24 billion billion electrons. (6.24 X )

10 Electrostatic Laws Law of electric charges: opposite charges attract each other, like charges repel each other Law of electric force: strong charges attract strongly, weak charges attract weakly

11 Electrostatic Laws Coulomb s Law of Electric Force - strength of the attraction or repulsion is directly related to the strength of the charges and inversely related to the distance between them.

12 Coulomb s Law of Electric Force The force between two charges is 100 Newtons 1. What happens if the distance d is doubled? 2. Double both charges? 3. Double d and charges?

13 Sharing a Charge Contact neutral object touches a charged object charged object transfers the charges. This can happen with positive and negatively charged objects. Charging by contact is permanent! The transfer of charges is conserved that is the amount of charge is the same before and after the transfer.

14 Transferring Charges An object s charge can be taken away completely by bringing it into contact with the ground! The earth is so huge it can soak up an object s electrical charge. This is called grounding!

15 Inducing a Charge A temporary transfer happens without direct contact. This is called induction Charging by induction produces two new charges instead of one. The example of this is the balloon on your hair!

16 Detecting Charges Small charges can be detected by means of an electroscope. When uncharged, the foil leaves stay down. When charged, the foil leaves rise up.

17 Electrostatic Generators The Van de Graaff Generator The charges move outward!

18 Protection from Lightning Benjamin Franklin knew that if the charge from a lightning strike could be directed into the ground, then the strike would be harmless. So, He invented the Lightning Rod.

19 Protection from Lightning Franklin s famous experiment is VERY DANGEROUS! Numerous people over the years have tried to duplicate it and have died from being struck by lighting! Do not attempt!

20 Video on Static Electricity rch/assetdetail.cfm?guidassetid=bbb0d f7-4fed db35d27cae6&tabDisplay=myContent

21 Magnets and Magnetism The first magnet ever used was actually a lodestone which is a natural magnet. It is a form of the mineral magnetite!

22 Magnets and Magnetism The Vikings were the first to use lodestones for navigation.

23 The Nature of Magnets Magnets come in various sizes and strengths. Magnets are used in televisions and speakers and computers.

24 The property of attracting objects by the magnetic force is known as magnetism. The region around a magnet that other objects are attracted to are the magnetic field. Compasses are affected by these fields. The iron filings represent lines of force. Magnetic Fields

25 Law of Magnetic Poles All magnets possess poles. One pole always seeks North. One pole always seeks South. The Law of Magnetic Poles states: Like poles repel and unlike poles attract.

26 Law of Magnetic Poles ical_science/magnetism/bar_magnet_inter active.html

27 Permeability Some substances can absorb or channel the lines of magnetic force better than others. The ability to do this is permeability. Highly permeable substances include iron, cobalt, and nickel.

28 The Earth as a Magnet The earth s magnetic field reaches out into space thousands of miles! We don t know why we are a magnet scientists think it may be that we have electricity circulating in the core.

29 The Earth as a Magnet The magnetic poles do not coincide with the geographic north and south poles. The poles wander about 5 miles every year!

30 The Magnetosphere The earth s magnetic field out in space is called the magnetosphere. The magnetosphere is distorted by the solar wind. The magnetosphere protects the earth from the harmful effects of the sun.

31 Van Allen Radiation Some of the sun s radiation is trapped in the magnetosphere. These trapped particles are called Van Allen belts.

32 Aurora Borealis Some particles of solar wind near the poles sometimes funnel down toward the earth. They crash into particles of air and produce brilliant shimmering lights known as the Aurora Borealis. The frequency of these depends on the solar winds.

33 Aurora Borealis

34 Understanding Magnets Magnets are caused by the spin of electrons around an atom. As a rule, the more unpaired electrons an atom has the more likely it is magnetic.

35 Understanding Magnets Domains A group of aligned atoms having a single magnetic field is a domain. A small bar magnet will have thousands of domains. A magnetic substance forms a magnet only if its domains are mostly aligned.

36 Types of Magnetic Materials Diamagnetic no unpaired electrons Paramagnetic one unpaired electron Ferromagnetic several unpaired electrons.

37 Methods of Magnetizing Magnetizing by contact may be temporary or permanent. Magnetizing by induction no contact needed. Magnetizing by electricity electricity flows through a wire and produces a magnetic field.

38 The Electromagnet An iron core with a wire wrapped around it can become a magnet if the wire has a current flowing through it.

39 The End!!!!