Magnetism

Magnetism Magnetism – Forces exerted by magnets Lodestones – rocks that are naturally magnetic Found in Magnesia in Greece Used by Chinese to navigate ships

Magnetic Poles Magnetic poles – one of the regions on a magnet that produces magnetic forces Like poles repel Opposite poles attract Compass: end that points northward is the north seeking pole, end that points southward is the south seeking pole

Magnetic Field Magnetic field – the space around a magnet, in which a magnetic force is exerted Shape of the field is revealed by magnetic field lines Every spinning electron is a magnet, most atoms’ electrons spin in different directions cancelling their magnetic force Opposite poles Similar poles Magnetic Field

Choose words to fill in the blanks: Magnetism is a force exerted by _______. Magnets are objects surrounded by a magnetic field. A magnetic ____ is the space around a magnet, in which a magnetic ____ is exerted. Every spinning ______is a magnet, most atoms’ electrons spin in different directions cancelling their magnetic force. Electron force Field Magnets

Choose words to fill in the blanks: Each magnet has two ____, a north and a south pole. The magnetic poles are one of the ______ on a magnet that produces magnetic forces. Like poles will ______ each other while opposite poles will ______ each other. attract regions poles repel

Electromagnetic Induction Magnets moved near—or even inside coils of wire induce (cause) a current in the coil. The more coils there are, the more current there is.

Electromagnetic Induction Moving wire and keeping the magnet stationary is the same as moving the magnet and keeping the wire stationary.

Faraday’s Law The induced voltage in a coil is proportional to the product of the number of loops and the rate at which the magnetic field changes within those loops

Electromagnet A moving charge produces a magnetic field. An electric current produces a magnetic field Magnetic field around a wire forms concentric circles

Electromagnets A current-carrying coil of wire with many loops is an electromagnet

Steam powered generator Generators Hand powered generator Device that rotates a coil of wire in a stationary magnetic field inducing a voltage in the coil Converts mechanical energy into electrical energy Steam powered generator

Electric Motors A permanent magnet is used to produce a magnetic field in a region where a loop of wire is mounted so that it can turn about an axis. Brushes – Parts of the wire that brush against contacts in a motor Armature – in larger motors, many coils of wire are wound about an iron cylinder

Steam powered generator Turbine Generator, where the armature is connected externally to a wheel The wheel may be powered by wind, falling water or steam Steam powered generator

Motor Effect vs Generator Effect Motor effect – when a current in a wire moves perpendicular to a magnetic field, there is an upward force on the electrons that move the wire Generator effect – When a wire with no initial current is moved in a magnetic field, the electrons in the wire experience a deflecting force perpendicular to their motion

Transformers Alternating current in the primary coil causes the north-south polarity of the electromagnet to change. Increasing or decreasing voltage through electromagnetic induction

Transformers

current electromagnet motor electric generator wire Choose words to fill in the blanks: As an ______ current or moving charge passes through a wire it produces a magnetic field. This magnetic field around a ____ forms concentric circles. A current-carrying coil of wire with many loops forms an ____________ . Magnets moved near—or even inside coils of wire induce (cause) a ______ in the coil. Electromagnets can be used as a ______ or _________ or simply as a magnet that can be turned on and off. current electromagnet motor electric generator wire

mechanical turn motor wire Choose words to fill in the blanks: An electric ______ is made when a permanent magnet is used to produce a magnetic field in a region where a loop of wire is mounted so that it can ____ about an axis. As current passes through the ____ , the wire spins as it is repelled and attracted to the magnet. The motor converts electrical energy into ___________ energy. mechanical turn motor wire

Choose words to fill in the blanks: An electric _________ is a device that rotates a coil of wire in a stationary magnetic field inducing a _______ in the coil. The generator ________ mechanical energy into _________ energy. converts generator electrical voltage

Energy Transformations Energy Changes!!!!!!!

Energy Energy is required to do work. Fuels are burnt to release energy The Sun is the ultimate source of most of our energy on Earth. 22

The Law of Conservation of Energy The total amount of energy on earth stays the same; it can be neither created nor destroyed. It can only be converted from one form to another. If energy seems to disappear, then scientists look for it – leading to many important discoveries.

Law of Conservation of Energy In 1905, Albert Einstein said that mass and energy can be converted into each other. He showed that if matter is destroyed, energy is created, and if energy is destroyed mass is created. E = mc2

Conservation of energy Energy cannot be created or destroyed. It can only be transformed from one form to another form. Conservation of energy also means that the total energy in the universe stays constant. 25

“Law of Conservation of Energy” Energy can not be created or destroyed, it can only change its form. To Conserve means: 1. to keep 2. to preserve 3. to maintain If energy seems to get lost during a process, then we should look for it !!

Pendulum oscillation GRAVITATIOINAL POTENTIAL ENERGY MAXIMUM ZERO MAXIMUM MINIMUM KINETIC ENERGY The total energy, gravitational potential plus kinetic, remains the same if there are no significant resistive forces 27

Choose words to fill in the blanks: According to the law of conservation of energy, during transformations the _______ amount of __________ stays the same. Energy can be not be ___________ or ____________ ; it can only change its form. created destroyed energy total

Energy Conversion Energy can be changed from one form to another. Changes in the form of energy are called energy conversions. Whenever energy is converted, some heat will be released or lost in the process

Energy conversions All forms of energy can be converted into other forms. The sun’s energy through solar cells can be converted directly into electricity. Green plants convert the sun’s energy (electromagnetic) into starches and sugars (chemical energy).

Other energy conversions In an electric motor, electrical energy is converted to mechanical energy. In a battery, chemical energy is converted into electrical energy. The mechanical energy of a waterfall is converted to electrical energy in a generator.

Energy Conversions In an automobile engine, fuel is burned to convert chemical energy into heat energy. The heat energy is then changed into mechanical energy.

Choose words to fill in the blanks: Energy can be changed from one _______to another. Changes in the form of _______ are called energy __________________ . Whenever energy is converted, some _____ will be released or lost in the process. conversions form energy heat

Forms of energy Energy can exist in many forms. 1. THERMAL or HEAT ENERGY This is the energy of an object due to its temperature. 2. LIGHT ENERGY This is energy in the form of visible electromagnetic radiation. 34

This is the energy transferred by an electric current. 3. ELECTRICAL ENERGY This is the energy transferred by an electric current. 4. SOUND ENERGY This is energy in the form of a sound wave. 35

5. KINETIC/MECHANICAL ENERGY This is the energy possessed by a moving object. Kinetic energy increases as the object’s speed is increased. Also often called ‘Movement energy’ 36

This is energy that is released when chemical reactions take place. 6. CHEMICAL ENERGY This is energy that is released when chemical reactions take place. Sources of chemical energy include: fuel, food and batteries. 7. NUCLEAR ENERGY This is energy that is released when nuclear reactions take place. This is the source of the Sun’s energy. 37

This is the energy possessed by an object due to its position. Gravitational potential energy being converted into kinetic energy. 8. POTENTIAL ENERGY This is the energy possessed by an object due to its position. Gravitational Potential Energy The gravitational potential energy of an object increases if it is raised upwards. Elastic Potential Energy This is the energy stored in a stretched or squashed object - also known as strain energy 38

Chemical  Heat Mechanical

Light Chemical Electrical

Light Thermal Electrical

Light Chemical

Electrical Mechanical

Thermal Electrical Mechanical

Electrical Sound Chemical Mechanical Light Thermal

Sound Electrical

Chemical Thermal

chemical mechanical electricity Solar Choose words to fill in the blanks: All forms of energy can be converted into other forms, examples include: The sun’s energy through _______ cells can be converted directly into ______________ . Green plants convert the sun’s energy (electromagnetic) into starches and sugars (_________________ energy). In an electric motor, electrical energy is converted to ___________________ energy. chemical mechanical electricity Solar

chemical mechanical fuel waterfall Choose words to fill in the blanks: All forms of energy can be converted into other forms, examples include: In a battery, __________ energy is converted into electrical energy. The mechanical energy of a ___________ is converted to electrical energy in a generator. In an automobile engine, _____ is burned to convert chemical energy into heat energy. The heat energy is then changed into _________________ energy. chemical mechanical fuel waterfall

Sankey Diagrams These are energy flow diagrams that show how well a device uses energy. The width of the flow arrows is proportional to the amount of energy Wasted energy is shown flowing downwards. INPUT Device USEFUL OUTPUT WASTED OUTPUT 50

Energy flow diagrams GENERAL DIAGRAM DEVICE CAUSING ENERGY CHANGE INPUT ENERGY WASTED ENERGY USEFUL OUTPUT ENERGY 51

Choose words to fill in the blanks: Energy flow ____________ show how _________ is transformed as it moves through a _____________ . Accounts for the thermal energy (_______ ) given off during that transformation. diagrams heat energy system

An electric light bulb lightbulb electrical energy light energy heat energy 53

Microphone sound energy electrical energy microphone heat energy 54

Car engine car engine chemical energy kinetic energy heat & sound energy 55

Photosynthesis light energy chemical energy plants heat energy 56

Deep thoughts Which of the forms of energy are most important to us in our daily lives? Electricity itself moves, but how does it cause other things to suddenly move? Name a few devices in which electricity causes something to move in a circle.

Energy Conversions Fuel (chemical to thermal) Water (thermal to mechanical) Steam turbine (mechanical to mechanical) Generator (mechanical to electrical) Toaster (electrical to thermal) Toast (thermal to chemical) Condenser (thermal to chemical) Emission control (chemical to thermal)

Complete the table below: Device Input energy Main output energy Electric motor electrical Car brakes heat gravitational potential Kinetic/mechanical Candle light Generator Kinetic/mechanical kinetic Falling object chemical kinetic 60

Useful and wasted energy Useful energy is energy transferred to where it is required in the form that it is wanted. Other forms of energy are referred to as ‘wasted’. Wasted energy spreads out into the surroundings. This is usually in the form of heat energy causing the energy changing device and its surroundings to become warmer. It is very difficult to ‘concentrate’ this energy again to make use of it. 61

Energy efficiency Energy efficiency is a measure of how usefully energy is converted by a device. efficiency = useful energy output total energy input As the useful energy output can never be greater than the energy input the efficiency can never be greater than 1.0 62

Energy efficient light bulbs These produce more useful light energy for the same amount of input electrical energy. They waste less energy to heat. 63

Improving efficiency Decrease loss to heat by: Reducing friction by using a lubricant (eg oil). Reducing electrical resistance in electrical circuits. Reducing air resistance by using streamlined shapes. Reduce loss to sound by tightening the loose parts of machinery. 64

Efficiency Measure Wasted Heat Required Choose words to fill in the blanks: Efficiency Measure Wasted Heat Required Useful energy is transferred to where it is ____ in the form that it is wanted. Other forms of energy are referred to as ‘____ ’ or given off in the form of heat. Strategies to reduce this ____ loss are intended to improve the ____ of a device. Energy efficiency is a ____ of how usefully energy is converted by a device.

Efficiency Measure Wasted Heat Required Choose words to fill in the blanks: Efficiency Measure Wasted Heat Required Useful energy is transferred to where it is required in the form that it is wanted. Other forms of energy are referred to as ‘wasted’ or given off in the form of heat. Strategies to reduce this heat loss are intended to improve the efficiency of a device. Energy efficiency is a measure of how usefully energy is converted by a device.

Conserve Reduce Light bulbs Wasting Choose words to fill in the blanks: Conserve Reduce Light bulbs Wasting Energy efficient ____ ____ are designed to produce more useful light energy for the same amount of input electrical energy by ____ less energy to heat. Use of energy efficient light bulbs is one strategy to conserve or ____ our consumption of energy. Within our homes there are many strategies we can use to ____ energy.

Conserve Reduce Light bulbs Wasting Choose words to fill in the blanks: Conserve Reduce Light bulbs Wasting Energy efficient light bulbs are designed to produce more useful light energy for the same amount of input electrical energy by wasting less energy to heat. Use of energy efficient light bulbs is one strategy to conserve or reduce our consumption of energy. Within our homes there are many strategies we can use to conserve energy.

Question 1 Calculate the efficiency of an electric motor if it produces 48J of useful kinetic energy when supplied with 80J of electrical energy. efficiency = useful energy output total energy input efficiency = 48J ÷ 80J efficiency of the motor = 0.6 69

Question 2 Calculate the useful light output of a light bulb of efficiency 0.20 when it is of an electric motor if it supplied with 400J of electrical energy. efficiency = useful energy output total energy input 0.20 = useful energy ÷ 400J useful energy = 0.20 x 400J light output = 80J 70

Percentage efficiency percentage efficiency = efficiency x 100 The greater the percentage of the energy that is usefully transformed in a device, the more efficient the device is. The maximum percentage efficiency is 100% 71

Question 3 Calculate the percentage efficiency of a light bulb if it produces 30J of light when supplied with 240J of electrical energy. efficiency = useful energy output total energy input efficiency = 30J ÷ 240J = 0.125 % efficiency = efficiency x 100 Percentage efficiency of light bulb = 12.5% 72