Electrical Energy and Magnetism

1. Electrical Energy and Magnetism

2. What is a Electricity? • Electricity- the energy associated with charged particles as they move from place to place • While these particles are usually electrons, any charged particles will do

3. Charges Exert Forces • Electric field- a region surrounding every electric charge in which a force of attraction or repulsion is exerted on the other electric charges • Electric field arrows point away from positive charges and toward negative

4. Electric Charge • Electric charge- a property of electrons (-) and protons (+) • When particles with these charges come near one another, a force of attraction or repulsion results • Like charges repel and opposites attract

5. Electric Charge • Electrons in atoms are bound more tightly to some atoms than others • Substances made of atoms with loosely bound electrons can transfer the electrons to substances they come into contact with • Remember that electrons are negatively charged • Protons are stuck in the nucleus

6. Charge Can Be Transferred By: • 1.) Contact: an object with an excess of electrons touches or rubs a neutral object, electrons are passed to the neutral object • 2.) Induction: the rearrangement of electrons on a neutral object caused by a nearby charged object without contact • Contact vs. induction simulation

7. Transferring Charges • What causes you to be shocked when you rub your feet across carpet? • The passing of an electrons through the air from a negatively charged object to a positively charge object causes current

8. Transferring Charges • The Van de Graaf generator deposits electrons on the ball, which travel through the person’s hand touching it • Body and hair temporarily get a negative charge • What up with the hair?

9. Static Electricity • Static electricity- the accumulation of excess stationary electric charge on an object • Negative charge in cloud builds up and repels that of the ground • The actual flash of lightning you see is the mass of positive ions from the ground surging upward to meet the negative particles • Lightning video

10. Static Electricity • An electroscope detects static charges

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12. Electric Current • Electric current- the net movement of electric charges in a single direction; represented by “I” and measured in amperes • In a metal wire without current, the electrons are in constant motion in all directions • Stereos, lights, etc. work when electric current is through them • A voltage difference is what causes electric current • Kinetic energymovement!

13. Static vs. Current Electricity • Static electricity is stationary or collects on the surface of an object, whereas current electricity is flowing very rapidly through a conductor • The flow of electricity in current electricity has electrical pressure or voltage

14. Voltage Difference • Voltage difference- related to the electrical force that causes charges to flow; represented by “V” and measured in volts • The direction of the current is always from higher voltage (+) to lower voltage (-) but the electrons travel in the opposite direction • Current and voltage applet

15. Batteries • Batteries are composed of a chemical substance which can generate voltage • There are two kinds of batteries: dry cell and wet cell batteries • This is an example of a dry cell and is called a dry cell because the electrolyte is a moist paste, and not a liquid • One electrode is the carbon rod, and the other is the zinc container

16. Batteries • Wet cell batteries are most commonly associated with automobile batteries • A wet cell contains two connected plates made of different metals or metallic compounds in a conducting solution

17. Electric Circuit • Electric circuit- a closed path that electric current follows • In a battery, there is a voltage difference between the two terminals (ends) • Negatively charged electrons flow from the negative terminal of a battery to the positive terminal and the current goes the opposite way

18. Resistance • Resistance- the tendency for a material to resist the flow of electrons to convert electrical energy into other forms, such as thermal; represented by “R” and measured in Ohms (Ω) • Almost all materials have some resistance • Resistors in electronics are used to reduce current through all or part of a circuit

19. Resistance • The metal which makes up a light bulb filament has a high electrical resistance which causes light and heat to be given off

20. What Influences Resistance? • Material of wire • Thickness – the thicker the wire the lower the resistance • Length – shorter wire has lower resistance • Temperature – lower temperature has lower resistance because the atoms of the wire are not moving as much and interferring with flow

21. Conductors vs. Insulators • Conductor- a material through which electrons move easily because the electrons are not held tightly by the atoms • Metals, skin, solutions • Insulator- a material in which electrons are not able to move easily because the electrons are held tightly by the atoms • Plastics and glass

22. Ohm’s Law • Ohm’s Law states that the voltage difference (V), current (I), and resistance (R) in a circuit are related • Current (amps) = voltage difference (volts) resistance (ohms) • I = V R Ohm’s Law Interactive

23. Check for Understanding

24. Types of Current • Alternating current (AC)- the kind of current from household electrical outlets in which the current changes direction (120 times/sec in the U.S.) • Direct current (DC)- the kind of current that battery powered devices use in which the current doesn’t change direction

25. AC

26. DC

27. Electric Circuits • There are two types of circuits: • Series circuit- the components are lined up along one path. If the circuit is broken, all components turn off

28. Electric Circuits • Parallel Circuit – there are several branching paths to the components. If the circuit is broken at any one branch, only the components on that branch will turn off

29. Electric Circuits • Electrical energy enters the home usually at a breaker box or fuse box and distributes the electricity through multiple circuits • A breaker box or fuse box is a safety feature

30. Household Circuits • Most household wiring is logically designed with a combination of parallel circuits

31. Electric Power • Electric power- the rate at which electrical energy is converted into another form of energy • Electrical power is the product of the current (I) and the voltage (V) • The unit for electrical power is the same as that for mechanical power – the watt (W) • Electrical power = current (amps) x voltage (V) • P =IV

32. Check for Understanding • How much power is used in a circuit which is 110 volts and has a current of 1.36 amps?

33. Check for Understanding • How much power is used in a circuit which is 110 volts and has a current of 1.36 amps? • P = I V • Power = (1.36 amps) (110 V) = 150 W

34. Electric Energy • Electric companies provide your house with electrical energy that you can then transform into other forms of energy….thermal (toaster), mechanical (washing machine), etc. • Electric energy = electrical power (kilowatts) x time (h) • E = P x t

35. Check for Understanding • A microwave has a power rating of 1000 Watts and the family uses it for 30 minutes a day. How much electrical energy has this microwave used?

36. Check for Understanding • A microwave has a power rating of 1000 Watts and the family uses it for 30 minutes a day. How much electrical energy has this microwave used? • Electric energy = electrical power (kilowatts) x time (h) • E = P x t • 1000 W = 1 kW and 30 minutes = 0.5 h • E = 1 kW X 0.5 h = 0.5 kWh

37. Check for Understanding • Super challenge! Put it together! • The current flowing through an appliance connected to a 120 V source is 2 A. How many kilowatt-hours of electrical energy does this appliance use in 4 hours?

38. Check for Understanding • Super challenge! Put it together! • The current flowing through an appliance connected to a 120 V source is 2 A. How many kilowatt-hours of electrical energy does this appliance use in 4 hours? • P = I V = 2 A x 120 V = 240 Watts = 0.240 kW • E = P x t = 0.240 kW x 4 h = 0.96 kWh

39. Electric Energy • Kilowatt-hours are read on an electric meter and you are charged for each kilowatt-hour by the electric company • It’s the total number of kilowatts used by all appliances times the total number of hours those appliances are used

40. Magnets • More than 2,000 years ago Greeks discovered deposits of a mineral called magnetite • In the twelfth century Chinese sailors used magnetite to make compasses that improved navigation • Today, the word magnetism refers to the properties and interactions of magnets

41. Characteristics of Magnets • Every magnet has two poles (N and S) and is surrounded by a magnetic field • This field exerts a force on other magnetic material • Magnetic poles are where the magnetic force exerted by the magnet is strongest • Depending on which ends of the magnets are close together, the magnets either repel or attract each other

42. What else do you know of that has a North and South Pole? • If you answered Earth you were right! It is one giant magnet with two magnetic poles surrounded by a magnetic field • This field is what causes a compass needle to point in different directions the poles of a magnet to point either north or south • N and S poles do move in time

43. Magnetic Field Direction • A magnetic field also has direction shown by the arrows • The north pole of a compass points in the direction of the magnetic field • This direction is always away from a north magnetic pole and toward a south magnetic pole

44. Magnetic Materials • All metal objects are not attracted by magnets • Only a few metal (iron, cobalt, and nickel) are attracted to magnets or can be made into permanent magnets • Every atom contains electrons and these electrons have magnetic properties • These magnetic properties don’t cancel out in magnetic materials

45. Magnetic Domains • Atoms that have magnetic fields can exert a force on other nearby atoms • This means all the N magnetic poles in the group point in the same direction • These groups of aligned atoms are called magnetic domains • Behave like magnets with a N and S pole • Contain an enormous number of atoms, yet the domains are too small to be seen with the unaided eye

46. Permanent Magnets • A permanent magnet can be made by placing a magnetic material, such as iron, in a strong magnetic field • The strong magnetic field causes the magnetic domains in the material to line up • The magnetic fields of these aligned domains add together and create a strong magnetic field inside the material • This field prevents the constant motion of the atoms from bumping the domains out of alignment. The material is then a permanent magnet

47. How are Electricity and Magnets Related? • By the 1700s, scientists everywhere had made many advances in both electricity and the study of magnetism • They then wondered if there was a possible link between the two fields. • The first to discover such a connection was a Danish physicist, Hans Christian Oersted (1777-1851).

48. Magnets and Electricity • It is now known that moving charges, like those in an electric current, produce magnetic fields • The direction of the magnetic field around the wire reverses when the direction of the current in the wire reverses • As the current in the wire increases the strength of the magnetic field increases

49. Magnets and Electricity • Magnets are used to generate, or produce, electricity and vice versa • When a conductive wire is wrapped around a piece of metal (like a nail) and current is run through it, magnetism can be induced in the metal • This is called electromagnetic induction

50. Electromagnets • Electromagnet- a temporary magnet made by passing electric current through a wire coiled around an iron bar • Can see them in junkyards • A crane holding a huge electromagnet can be used to pick up scrap metal when current flows through it • When the crane operator wants to drop the scrap, they shut off the current