Unit 2: Electricity and Energy Resources

Transcription

1 8 Table of Contents Unit 2: Electricity and Energy Resources Chapter 8: Magnetism and Its Uses 8.1: Magnetism 8.2: Electricity and Magnetism 8.3: Producing Electric Current

2 8.1 Magnets Magnetism Magnetism: property of matter- shows force of attraction/repulsion due to electron arrangement. Magnetite: magnetic rock found in Magnesia Lodestone: magnetic rock that pointed to the lodestar

3 8.1 Magnetism Magnetic Force Kinds of Magnets: Natural- found in nature Permanent- stay magnetized for long time Temporary- lose magnetism quickly

4 8.1 Magnetism Magnetic Field Magnetic field: region where magnetic forces can act Lines of force/ magnetic field lines: define magnetic field Magnetic poles: ends where force is strongest North pole South pole

5 8.1 Magnetism Magnetic Field Magnetic poles: ends where force is strongest North pole South pole Same poles= repel South and south Different poles= attract North and south

6 8.1 Magnetism Earth s Magnetic Field Earth acts like a giant bar magnet Geographic polearea earth turns around Magnetic pole- N & S of Earth s magnetic field

7 8.1 Magnetism Earth s Magnetic Field Mag. N= Geo. S Mag. S= Geo. N Compass needle pts towards Geo. N due to attraction to Mag. S Not exactly north- off by 9º

8 8.1 Magnetism Magnetic Domains A Model for Magnetism Groups of atoms with aligned magnetic poles = magnetic domains Magnetism is due to spin of electrons Paired: opposite direction = cancel out magnetism Unpaired: magnetic field felt in all directions if line up

9 8.1 Magnetism Lining Up Domains Magnetic Induction: process to make a material a magnet. Ex: place a magnet against a nail, atoms in nail line up= temporary magnet Works with paper clips and other iron containing materials

10 8.1 Section Check Question 1 What is the difference between a magnetic field and a magnetic pole?

11 8.1 Section Check Answer A magnetic field is the area surrounding a magnet that exerts a force on other magnets and magnetic materials. A magnetic pole is the region on a magnet where the magnetic force is strongest.

12 8.1 Section Check Question 2 Groups of atoms with aligned magnetic poles are called. A. magnetic charges B. magnetic domains C. magnetic fields D. magnetic materials

13 8.1 Section Check Answer The answer is B, magnetic domains. Magnetic materials contain magnetic domains.

14 8.2 Electricity and Magnetism Electric Current and Magnetism 1820: Han Christian Oersted found that electricity and magnetism related electric current causes magnetic field

15 8.2 Electricity and Magnetism Electromagnets Electromagnet: temporary magnet; wire coil wrapped around iron core Increase strength by: Increasing loops around core Increase current/voltage No current=no magnetism

16 8.2 Electricity and Magnetism Galvanometers Your car s dashboard gauges are types of galvanometers. Galvanometer: device that uses electromagnet to measure small electric current Measures direction

17 Electricity and Magnetism 8.2 Electric Motors Electric motor: changes electrical energy into mechanical energy Almost all household appliances with moving parts contain electric motor

18 8.2 Electricity and Magnetism A Simple Electric Motor Parts: Electromagnet rotating on shaft Battery- produces current to make coil electromagnet Brushes- conductors connecting battery and commutator Commutator- conducting metal ring Split in DC, complete in AC

19 Electricity and Magnetism 8.2 Making the Motor Spin Current flows, attraction/repulsion causes electromagnet to spin, spinning turns shaft of motor to do work (electrical E mechanical E)

20 8.2 Electricity and Magnetism Making the Motor Spin Commutator= reversing switch Changes direction of current Coil rotates until poles are opposite the magnet- commutator reverses again to keep rotating.

21 8.2 Section Check Question 1 Who correctly hypothesized that electric current produces a magnetic field? A. Neils Bohr B. Heinrich Hertz C. Hans Christian Oersted D. Max Planck

22 8.2 Section Check Answer The answer is C. In 1820, Oersted hypothesized that electric current produces a magnetic field and that the direction of the field changes with the direction of the current.

23 8.2 Section Check Question 2 How can you make an electromagnet? Answer An electromagnet is a temporary magnet made by wrapping a wire coil carrying a current around an iron core.

24 8.2 Section Check Question 3 Which of the following is a device that uses an electromagnet to measure current? A. electric motor B. galvanometer C. generator D. transformer

25 8.2 Section Check Answer The answer is B. In a galvanometer, the electromagnet is connected to a small spring.

26 8.3 Producing Electric Current From Mechanical to Electrical Energy 1830 s: Faraday & Henry Found: moving loop of wire through magnetic field causes electric current = electromagnetic induction

27 8.3 Producing Electric Current Generators Generator: converts mechanical energy to electrical by electromagnetic induction Rotating loop of wire (mechanical energy) produces electric current

28 Producing Electric Current 8.3 Generating Electricity for Your Home Electrical energy comes from a power plant with huge generators.

29 8.3 Producing Electric Current Generating Electricity for Your Home Burned fossil fuels heat water Steam rotates turbine (thermal mechanical energy) Generator changes mechanical energy of rotating turbine into electrical energy.

30 8.3 Producing Electric Current Direct and Alternating Currents Direct current (DC) flows only in one direction (- to +) Wet cell battery Alternating current (AC) reverse direction of electrons/current in regular pattern. House outlets in N. America= 60 Hz=change direction 120 times/s

31 8.3 Producing Electric Current Transformers Transformer: device that increases or decreases voltage of alternating current Made of: 2 coils insulated wire wrapped around same iron core Primary coil Secondary coil

32 8.3 Producing Electric Current Transformers Primary coil: creates magnetic field when AC passes through (electromagnetism) Secondary coil: current flows through (electromagnetic induction)

33 8.3 Producing Electric Current Step-Up Transformer Step-up transformer: more loops in secondary coil= increases voltage in secondary

34 8.3 Producing Electric Current Step-Down Transformer step-down transformer: fewer loops in secondary coil= decreases voltage

35 8.3 Producing Electric Current Transmitting Alternating Current How step-up and step-down transformers are used from power plants to your home.

36 8.3 Section Check Question 1 What is electromagnetic induction? Answer Electromagnetic induction is the generation of a current by a changing magnetic field.

37 8.3 Section Check Question 2 In a power plant, what is the function of the turbine?

38 8.3 Section Check Answer The turbine is a large wheel that rotates when pushed by water, wind or steam. The plant s generator changes the mechanical energy of the rotating turbine into electrical energy.

39 8.3 Section Check Question 3 Which will increase the voltage of an alternating current? A. battery B. generator C. motor D. transformer

40 8.3 Section Check Answer The answer is D. Transformers can also decrease voltage, such as in a step-down transformer.

41 End of Chapter Summary File