Joy of Science Discovering the matters and the laws of the universe

Joy of Science Discovering the matters and the laws of the universe Key Words Universe, Energy, Quantum mechanics, Chemical reaction, Structure of matter Unless otherwise noted, copied pictures are taken from wikipedia.org

Quiz

Quiz 1 n A measure of the ability of a material to absorb heat is referred as its 1. thermal energy 2. heat capacity 3. heat transfer 4. temperature

Quiz 2 n Which of the following statements is not consistent with the second law of thermodynamics? 1. All isolated systems will tend to remain ordered indefinitely 2. Heat will not flow spontaneously from a cold body to a hot body 3. No engine is one hundred percent efficient in converting energy to work 4. The evolution of more complicated forms of life on Earth does not annul the second law

Quiz 3 n A device that converts stored energy into the kinetic energy of electrons passing through an outside wire is called a(n) 1. battery 2. compass 3. electromagnet 4. motor

November 14, 2016 Electricity and Magnetism What is lightning? Electrical charge, electricity, static electricity; Electrical field, Coulomb s law Magnet, magnetic force, magnetic field; Battery, AC, DC, electric motor

Contents n Introduction n Electricity, and Magnetism n Electromagnetism

Introduction - Static electricity - Movements of electrons

1. Introduction Newton s laws of motion tell us that nothing happens without a force. We have learned the law of gravity.

1. Introduction Newton s laws of motion tell us that nothing happens without a force. We have learned the law of gravity. However, Does gravity force explain how your hair tends to stand on end, or how does a compass needle swing around to the north? àthese phenomena occur by a different type of forces in nature from Gravitational force

Introduction Static Electricity Observations Rub a balloon filled with air on your hair. Then hold it up to a wall. The balloon will stay there by itself. Now rub two balloons on your hair, hold them by strings at the end and put them next to each other. They'll move apart.

Introduction Static Electricity Observations Rub a balloon filled with air on your hair. Then hold it up to a wall. The balloon will stay there by itself. Charged Charged Now rub two balloons on your hair, hold them by strings at the end and put them next to each other. They'll move apart. Charged Charged

Introduction Static Electricity Observations Rub a balloon filled with air on your hair. Then hold it up to a wall. The balloon will stay there by itself. Attractive Force Charged Charged Now rub two balloons on your hair, hold them by strings at the end and put them next to each other. They'll move apart. Charged Repulsive Force Charged

Introduction Static Electricity (cont d) n Electrical charge: The objects in the given situation demonstrated in previous slide, are called charged, and they possess electrical charge. n Electricity: The force that moves such charged objects toward and away from each other is electricity (named after the Greek word for amber) n Static electricity: The electrical charge doesn t move once it has been placed. The force is called static electricity.

Introduction Movement of electrons 1 n There are two kinds of electrical charge: + and n All objects are made of fundamental building blocks called atoms, and all atoms are made up of smaller particles that have electrical charge. Neutral atom

Introduction n Any object, Atoms, Building blocks of atoms Any object Atom: nucleus + electrons (+) (-) Nucleus : + protons (positive) + neutrons (neutral) Electron: - (negative)

Introduction n Most atoms are electrically neutral è positive charge of nucleus cancels negative charge of electrons: number of (+) charges = number of (-) charges Example:

Introduction n Electrons are loosely bound to atoms In metal, electorons can move freely or can react with other elements. nucleus Nucleons tightly bound within the nucleus electron Loosely bound to the atom à can be stripped off à can be added to

Introduction Movement of electrons 2 * When electrons are stripped off of a material, ( # of (+) charges > # of (-) charges) the object has a net excess of positive charge è the object acquired a positive electrical charge * When extra electrons are added to it ( # of (+) charges < # of (-) charges) è the object acquired a negative electrical charge * + Attractive Force + + Repulsive Force

Electricity, and Magnetism - Electricity - Magnetism - Electric circuits

Electricity Coulomb s law Charles Augustin de Coulomb (1736-1806), a French physicist, after a series of experiments, discovered that electrical force is very similar to the gravitational force. Coulomb s law n The force between any two electrically charged objects is proportional to the product of their charges divided by the square of the distance between them.

Electricity Coulomb s law (cont d) Coulomb s law Force (newtons) = F = k x 1 st charge x 2 nd charge distance 2 k x (q 1 x q 2 ) d 2 Distance d in meters, charge q in unit of electrical charge called coulomb (C), and k is the coulomb constant (9.00 X 10 9 newton-meter 2 /coulomb 2 ). We define 1 C as the charge on 6.24 X 10 18 electrons.

Electricity Electric field Imagine that an electrical charge is sitting at a point.

Electricity Electric field Imagine that an electrical charge is sitting at a point. If you brought a second charged object to a spot near the first,

Electricity Electric field Imagine that an electrical charge is sitting at a point. If you brought a second charged object to a spot near the first, the second object would feel a force.

Electricity Electric field Imagine that an electrical charge is sitting at a point. If you brought a second charged object to a spot near the first, the second object would feel a force. Electrical field: Every charged object exerts forces on its surroundings to create an electric field.

Electricity Electric field (cont d) An electric force is represented by an electric field, with arrows that represent the direction and strength of the field at every point.

Magnetism Magnetism Just as electrical phenomena, we find another type of interesting phenomena in our nature, so called magnetism. Observations Ancient people learned about magnetism from naturally magnetized pieces of iron ore, which attract pieces of iron. The word magnet in Greek meant "stone from Magnesia, a part of ancient Greece.

Magnetism Terms n Magnet: a piece of iron that attracts objects made of iron towards it n Magnetic force: a force described by magnetism n Magnetic Poles: Each end of a magnet is called a pole. One end points north and the other points south. The compass is the first magnetic device on record. 1. Every magnet has two poles 2. Like magnetic poles repel each other, while unlike poles attract

Magnetism Magnetic poles 1 Every magnet has two poles (di-poles) S N

Magnetism Magnetic poles 1 S N S monopole??? N monopole???

Magnetism Magnetic poles 1 Why Magnetic monopoles don t exist??? S N S monopole??? N monopole???

Magnetism Magnetic poles 2 n Earth is a giant magnet! One end of a compass points to one of its pole in the north, the other points to the south.

Magnetism Magnetic field 1 n Magnetic field: magnets display a curving field pattern n A magnetic force is represented in terms of a magnetic field, with arrows that indicate the direction and strength of magnetic forces at any point around the magnet

Iron filings show the pattern of magnetic field Magnetism Magnetic field 1 n Magnetic field: magnets display a curving field pattern

Magnetism Magnetic field 1 Iron filings show the pattern of magnetic field

Magnetism Magnetic field 2 n Earth s magnetic field

Magnetism Polar lights n Aurora is caused by particles from the Sun interacting with Earth s magnetic field

Magnetism No magnetic monopole Pairs of Poles n All magnets found in nature have both north and south poles There are no isolated magnetic poles in nature Or equivalently, There is no magnetic monopole in nature Why Magnetic monopoles don t exist? è Connection between electricity and magnetism!

Electric circuit Electric Circuit Most of our contact with electricity comes from moving charges, not static electricity n Electrical current: a flow of charged particles n Battery: an electrochemical cells that convert stored chemical energy into electrical energy

Electric circuit Electric circuits 1 n Electric circuit: An unbroken path of material, called electrical conductors, that carries electricity (Ex. Copper wire). Closed path Energy source Device Every circuit consists of three parts: a source of energy (ex. battery), a closed path made of metal wire, and a device such as a motor or a light bulb.

Electric circuit Electric circuits 1 n Electric circuit (cont d): * The unit of the amount of electrical current that flows in a wire: ampere (amp) 1 amp of current = 1 coulomb of charge per second

Electric circuit Electric circuits 1 n Electric circuit (cont d): * Analogy between the current of water and electrical current electrical current passing through a circuit : water current flowing through a pipe voltage, pressure, by energy source in circuit : water pressure in plumbing system wires through electrons flow : pipes carrying water è Resistance of current depends on materials of wires

Electric circuit Electric resistance n Electrical resistance is measured in a unit called ohm è Higher the resistance, the more electric energy is converted into heat Ohm s law: voltage (volts) = current (amps) X resistance (ohms) V = I x R

Electric circuit Power of electric appliance n Power consumed by an electric appliance is equal to the product of the current and the voltage power (watts) = current (amps) X voltage (volts) P = I x V n Two kind of electric circuits * series circuit: all loads linked along a single loop (Ex. Christmas lights) * parallel circuit: different loads are situated on different wire loops

Electric circuit Lightning _ + + +

Electric circuit Lightning Lightning stroke is the electrical current between cloud and ground when collisions of particles in the clouds produce a negative charge at the bottom of the cloud and a corresponding build of positive charge in objects on the ground. _ + + +

Electromagnetism - Connection between electricity and magnetism - Electric effects from magnetism - Magnetic effects from electricity

Electromagnetism Connections between Electricity and Magnetism Electricity and Magnetism seem as different from each other, but in fact they are intimately related to each other!

Electromagnetism Magnetic effect from electricity 1 n Magnetic effect from electricity Whenever an electrical current flows through a wire a magnetic field appears around that wire

Electromagnetism Magnetic effect from electricity 1 n Magnetic effect from electricity Electrical current

Electromagnetism Magnetic effect from electricity 1 n Magnetic effect from electricity Induced magnetic field Electrical current

Electromagnetism Magnetic effect from electricity 1 n Magnetic effect from electricity Ampere s law Induced magnetic field Electrical current

Electromagnetism Magnetic effect from electricity 1 n Magnetic effect from electricity Whenever an electrical current flows through a wire à in an experiment, battery was connected to generate an electrical current a magnetic field appears around that wire à in the experiment, a compass needle on a nearby table moved

Electromagnetism Magnetic effect from electricity 2 n Electromagnet: We can create a magnetized piece of iron simply by running electrical current around a loop of wire èthe stronger the current, the stronger the magnetic field will be

Electromagnetism Magnetic effect from electricity 2 n Electromagnets: Ex) Electric motor: A pair of permanent magnets and a rotating loop of wire inside the poles of the magnets When the induced magnetic field faces the same pole (N-N and S-S) as the permanent magnet s, the motor rotates.

Electromagnetism Magnetic effect from electricity 2 n Electromagnets: Ex) Electric motor: Electrical energy à Machinery energy A pair of permanent magnets and a rotating loop of wire inside the poles of the magnets When the induced magnetic field faces the same pole (N-N and S-S) as the permanent magnet s, the motor rotates.

Electromagnetism Question: Why magnetic monopoles don t exist?

Electromagnetism Question: Why magnetic monopoles don t exist? Magnetism in nature is ultimately related to the arrangement of electrical charges rather than to anything to matter itself.

Electromagnetism Electrical effects from magnetism 1 n Electrical effects from magnetism Michael Faraday (1791-1867) discovered that Electrical fields and electrical currents can be produced by changing magnetic fields.

Electromagnetism Electrical effects from magnetism 1 n Electrical effects from magnetism (cont d) Exp. setup Faraday placed two electromagnets two coils of wire-, then he watched that when an electrical current flowed through one of the coils of wire è a strong electrical current developed in the second coil of wire even though it was not connected to a battery

Electromagnetism Electrical effects from magnetism 1 n Electrical effects from magnetism (cont d) Exp. setup Faraday placed two electromagnets two coils of wire-, then he watched that when an electrical current flowed through one of the coils of wire (è when magnetic field appear) è a strong electrical current developed in the second coil of wire even though it was not connected to a battery

Electromagnetism Electrical effects from magnetism 1 n Electrical effects from magnetism Electrical fields and electrical currents can be produced by changing magnetic fields. Induced magnetic field Galvanometer: read induced electric current at the moment when the switch is on battery Two coils

Electromagnetism Electrical effects from magnetism 2 n Electrical effects from magnetism Ex) Electric generators: Electrical currents are produced by rotating coils between two poles of permanent magnets, in other words, by changing magnetic fields AC(alternating current): direction keeps alternating Ex) Home appliances DC (Direct current): in only one direction Ex) Produced by batteries

Electromagnetism Electrical effects from magnetism 2 n Electrical effects from magnetism Ex) Electric generators: AC generator DC generator

Electromagnetism Electrical effects from magnetism 2 n Electrical effects from magnetism Ex) Electric generators: Machinery energy àelectrical energy AC generator DC generator

Electromagnetism Maxwell s equations Electromagnetic force A fundamental force in nature n Maxwell s equations: Four fundamental laws of electricity and magnetism 1. Coulomb s law: like charges repel, unlike attract 2. There are no magnetic monopoles in nature 3. Magnetic phenomena can be produced by electrical effects 4. Electrical phenomena can be produced by magnetic effects

Next topic is, Waves and electromagnetic radiation : Chapter 3 www.sci.hokudai.ac.jp/~epark/ekpark/jos.html