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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 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 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
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
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
November 14, 2016
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?
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
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 è Electrical or magnetic forces:
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 è Electrical or magnetic forces: Electromagnetic force!
Static Electricity
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
Observations
Static Electricity
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
Observations
Static Electricity
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
Observations
Charged Charged
Charged Charged
Static Electricity
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
Observations
Charged Charged
Charged Charged Repulsive Force
Attractive Force
Static Electricity
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
Observations
Charged Charged
Charged Charged Repulsive Force
Attractive Force
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.
Introduction
Neutral atom
n Any object, Atoms, Building blocks of atoms
Atom: nucleus + electrons (+) (-)
Nucleus : + protons (positive) + neutrons (neutral)
Electron: - (negative)
Any object
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.
Nucleons tightly bound within the nucleus
Loosely bound to the atom à can be stripped off à can be added to
Introduction
nucleus electron
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 *
Introduction
+ __ + + Attractive Force Repulsive Force
Electricity, and Magnetism - Electricity - Magnetism - Electric circuits
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 = Distance d in meters, charge q in unit of electrical charge called coulomb (C), and k is the coulomb constant (9.00 X 109 newton-meter2/coulomb2). We define 1 C as the charge on 6.24 X 1018 electrons.
Electricity
k x 1st charge x 2nd charge distance2
k x (q1 x q2) d2
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.
Electricity
Magnetism
Just as electrical phenomena, we find another type of interesting phenomena in our nature, so called magnetism. 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
Observations
Magnetism
Just as electrical phenomena, we find another type of interesting phenomena in our nature, so called magnetism. 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
Observations
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
Terms
Magnetic poles 1
Every magnet has two poles (di-poles)
Magnetism
S N
Magnetic poles 1
Magnetism
S N
S – monopole??? N – monopole???
Magnetic poles 1
Why Magnetic monopoles don’t exist???
Magnetism
S N
S – monopole??? N – monopole???
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
Magnetism
Magnetic field 1
n Magnetic field: magnets display a curving field pattern
Magnetism
Iron filings show the pattern of magnetic field
Magnetic field 1
Magnetism
Iron filings show the pattern of magnetic field
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!
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!
Magnetism
Let’s see the connection in the next section. Electromagnetism!
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). 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
Energy source
Device
Closed path
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
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 circuits 1
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.
Electric circuit
_ _ _
+ + +
Electromagnetism - Connection between electricity and magnetism - Electric effects from magnetism - Magnetic effects from electricity
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
Electromagnetism
Electrical current
Magnetic effect from electricity 1
n Magnetic effect from electricity
Electromagnetism
Induced magnetic field
Electrical current
Magnetic effect from electricity 1
n Magnetic effect from electricity
Electromagnetism
Ampere’s law
Induced magnetic field
Electrical current
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
Electromagnetism
When the induced magnetic field faces the same pole (N-N and S-S) as the permanent magnet’s, the motor rotates.
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
Electromagnetism
When the induced magnetic field faces the same pole (N-N and S-S) as the permanent magnet’s, the motor rotates.
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)
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
Exp. setup
Electrical effects from magnetism 1
n Electrical effects from magnetism (cont’d)
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
Exp. setup
Electrical effects from magnetism 1
n Electrical effects from magnetism “Electrical fields and electrical currents can be produced by changing magnetic fields”.
Electromagnetism
Induced magnetic field
Galvanometer: read induced electric current at the moment when the switch is on
battery
Two coils
Electrical effects from magnetism 2
n Electrical effects from magnetism Ex) Electric generators: AC(alternating current): direction keeps alternating Ex) Home appliances DC (Direct current): in only one direction Ex) Produced by batteries
Electromagnetism
Electrical currents are produced by rotating coils between two poles of permanent magnets, in other words, by changing magnetic fields
Electrical effects from magnetism 2
n Electrical effects from magnetism Ex) Electric generators:
Electromagnetism
AC generator DC generator
Electrical effects from magnetism 2
n Electrical effects from magnetism Ex) Electric generators: Machinery energy àElectrical energy
Electromagnetism
AC generator DC generator
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
Electromagnetism
Next topic is, Waves and electromagnetic radiation
: Chapter 3
www.sci.hokudai.ac.jp/~epark/ekpark/jos.html