Electricity Have you ever stuck a balloon to

Electricity

• Have you ever stuck a balloon to the wall after rubbing it on your head? • Have you ever gotten an electric shock off your door knob? • Have you ever seen lightning?

All these things happen because of Static Electricity Chapter 20

Section 20. 1 Objectives • Describe how and why an object can be charged • Define charging based on the separation of charges from atoms • Identify the differences between conductors and insulators

What is Static Electricity? • Static electricity occurs when there is a build up of electric charge on the surface of a material. • It is called static electricity because the charges don’t move. • In contrast, the electricity we use everyday involves moving charges.

Charge • Most things have the same number of electrons and protons in them. • They don’t have any overall charge. (neutral) • When do atoms have an overall charge? • If atoms/objects do have an overall charge interesting things can happen. • Video clip: http: //www. youtube. com/watch? v=tu. Zx. FL 9 c. Gk. I http: //www. youtube. com/watch? v=b 89 x 8 CAS 6 x. U

Static electricity • Static electricity is caused when certain materials are rubbed against each other. • Electrons can be rubbed off one material and on to another. • The material that has gotten extra electrons is now negatively charged • The material which has lost electrons is positively charged.

Static electricity • It is this imbalance of positive and negative charges that causes: – Balloons to stick to walls. – Your hair to stand on end when brush your hair on a dry day. – Static Cling – The electric shock you sometimes get from the door handle. • http: //phet. colorado. edu/en/simulation/travoltage

Static electricity Ben Franklin’s naming convention: – Materials like vinyl, hard rubber, plastics become negatively charged • They are actually gaining electrons – Materials like fur, hair, glass and wool become positively charged • Their electrons are getting stripped off leaving excess protons

Conductors and Insulators: • A material through which a charge will not move easily is called an electric insulator. • Glass, dry wood, most plastics, cloth, and dry air are all good insulators. Conductors: • A material that allows charges to move about easily is called an electric conductor. • Metals are good conductors because at least one electron on each atom of the metal can be removed easily. • These electrons act as if they no longer belong to any one atom, but to the metal as a whole; consequently, they move freely throughout the piece of metal.

Conductor vs. Insulator • Conductor - allows charges to move freely and carries an electric current • Insulator - does not transfer charge easily • Conductor or Insulator depends on the inter -atomic bonding and on how tightly the atoms of a substance hold their VALENCE electrons.

Electricity • Conductors: Ex. Some Metals – Each atom contributes one or more electrons to a general “sea” of electrons attached to no particular atoms • Insulators: – All electrons are attached to particular atoms.

Electricity - electrons moving through a metal wire.

Conductor vs. Insulator Conductor or Insulator?

Conductors and Insulators • The figure below contrasts how charges behave when they are placed on a conductor with how they behave on an insulator.

Concpet Check: Section 20. 1 Question 1 What will happen if you rub two identical plastic rulers with a woolen cloth and bring them together? A. The rulers will attract each other. B. The rulers will repel each other. C. The rulers will neither attract nor repel. D. The rulers will partially attract and partially repel.

Concept Check Section 20. 1 Question 2 Which of the following statements about charges is true? A. Charges are created by gaining electrons. B. Charges are destroyed by losing electrons. C. Charges are separated through a transfer of electrons. D. Charges cannot be created, destroyed, or separated.

Concept Check: Section 20. 1 Question 3 A negative charge is generated in a rubber rod by rubbing it with wool. When two materials, A and B, are brought near the rubber rod, material A is attracted to the rod, whereas material B is repelled. What can you say about the charges on the two materials? A. A is positively charged, while B is negatively charged. B. Both A and B are negatively charged. C. Both A and B are positively charged. D. B is positively charged, while A is negatively charged.

Electrical Charges • Homework: • Read pages 407 - 411 • Do Concept Review Problems: 1. 1 – 1. 3 • We will review tomorrow 5/9

Electric Forces 20. 2 Objectives: • Explain separation of charge and charging by induction • State Coulombs Law and how force depends on charges and distance • Understand the cause of attractive force on neutral objects

Force Review • What is a Force? Answer: A push or a pull • Ex. Gravity – The Force of Gravity pulls (attracts) you to the Earth – We call it your Weight

Forces • Four Fundamental Forces – Gravity – Electromagnetic − Strong Nuclear − Weak Nuclear • Which of the above is the strongest force? Nuclear Strong Force – binds protons & neutrons • 100 x stronger than Electromagnetic & many, many times stronger than the Weak Force Nuclear Weak Force – affects sub-sub atomic particles • Which is the weakest? Gravity!

Electro-Static Force • Electrical Forces are billions upon billions of times stronger than Gravity… – Holds atoms together (protons & electrons) – It’s what attracts atoms to each other – creates a solid table that your hand can’t go through

Static Electricity • Charge is… – the fundamental electric quantity – symbolized by q or Q – unit of measure is the Coulomb (C) • Electrons and Protons are referred to as elementary charges charge of an electron, qe = -1. 62 x 10 -19 C charge of a proton, qp = +1. 62 x 10 -19 C

Electro-Static Force • An objects electric charge depends on the overall imbalance of its protons and electrons • The greater the imbalance the greater the overall charge • Most of the time Attractive & Repulsive Forces balance each other out, so… no noticeable effect… But if we can create an imbalance… • We get Electro-Static Force

Electro-Static Force • Electric Force: – The force of attraction or repulsion between objects due to charge • like-charged things repel • oppositely-charged things attract.

Electromagnetism • Strength of Electric Force Depends on – Charge – Distance Gravity is a good analogy

Recall… Gravity • Gravity = Force that pulls objects toward each other. • Universal Law of Gravitation: The force of gravity acts between all objects in the Universe

Recall… Gravity Strength of the Gravity depends on… 1. The masses of the objects involved 2. The distance between the objects involved F=G where G = 6. 67 x 10 -11

Coulombs Law Strength of the Electric Force depends on… 1. The CHARGES of the Particles involved 2. The distance between the Particles involved F=k where k = 9. 0 x 109

Coulombs Law • Strength of Electric Force Depends on – Charge Bigger Charge = Stronger Force – Distance e Like Charges D k i l t s ity u J av r G Opposite Charges D , Frepulse , Fattract This will play a big role in batteries

Coulombs Law • Which subatomic particle is easiest to remove? Valence Electron • Why? According to Coulombs Law – the further + apart the e and p , the less electromagnetic force between them.

Recall. . . • 2 positive charges put together will repel each other. • A positive charge near a negative charge will attract each other.

Concept Check Section 20. 2 Coulomb’s Law If two positively charged objects, A and B, are brought near each other, the forces they exert on each other are repulsive. If, instead, B is negatively charged, the forces are attractive.

Concept Check Section 20. 2 Coulomb’s Law Problem: Sphere A, with a charge of +6. 0 µC, is located near another charged sphere, B. Sphere B has a charge of − 3. 0 µC and is located 4. 0 cm to the right of A. a. What is the force of sphere B on sphere A?

Concept Check Section 20. 2 Coulomb’s Law Problem: Identify the known and unknown variables. Known: Unknown: q. A = +6. 0 µC FB on A = ? q. B = − 3. 0 µC r. AB = 4. 0 cm

Concept Check Section 20. 2 Coulomb’s Law Problem: Find the force of sphere B on sphere A.

Concept Check Section 20. 2 Coulomb’s Law Substitute q. A = 6. 0 μC, q. B = -3. 0 μC, r. AB = 4. 0 cm - - Because spheres A and B have unlike charges, they attract, the force of B on A is to the right and is negative (negative force sign = attraction, positive = repulsion)

How do charges behave? • What is a water molecules overall charge? • Bending Water Demo – • If a charge does build up on an object, how does it affect other objects if most of them are neutral?

Electric Fields • A charged particle produces an electric field around it • Electric Field: a region in space around a charged object that causes a stationary object to experience an electric force. – like a Gravitational Field only caused by charge, not mass

Electric Fields • It is because of this electric field that …. • 2 positive charges put together will repel each other. • A positive charge near a negative charge will attract each other.

Electric Fields • When neutral atoms encounter this electric field, the individual charges (p+, e-) within the atom are still affected by the electric field • When neutral molecules (like water) encounter this electric field, the individual charges within the molecule are still affected by the electric field

Charging • Charging by Induction – Charges move within a neutral object due to the electric field of the charged object. – NO CONTACT IS MADE See example… http: //phet. colorado. edu/en/simulation/balloons …what happens within the neutral wall?

Charging • You can also charge by friction (rubbing to transfer charges from one object to another) • You have seen this by rubbing wool against rubber/plastic • You can charge by conduction. This is direct transfer of charge by touching metal with a charged object

Section 20. 2 Homework • Read pages 413 to 420 • Do Practice Problems 1 -4, page 420 • Due Friday 5/30 (last HW for Seniors!) • Tomorrow: The Versorium Lab

Static Electricity When do you seem to get “shocked” the most? Why?

What did your mom use to do (maybe still does) when you took your hat/sweater off and your hair looked like this?

Static electricity - Humidity If it is very humid, the charge imbalance will not remain for a useful amount of time… Is water a good conductor or bad conductor? The moisture provides a low resistance path for electron flow. This path allows the charges to recombine and thus neutralize the charge imbalance.

Static electricity We usually only notice static electricity in the winter when the air is very dry. During the summer, the air is more humid. The water in the air helps electrons move off you more quickly, so you can not build up as big of a static charge. Big Hair in the 80’s Winter vs. Summer

Static Cling Fabric softeners work by coating the surface of the cloth fibers with a thin layer of chemicals; these chemicals have lubricant properties and are electrically conductive

Static electricity • What do you do to prevent frizzy hair? Conditioner • Why? Helps hair retain moisture

Conservation • Whether we are talking about Static Electricity or the Current Electricity we’ll discuss coming up… • There is a Conservation of Charge… • Electrons are neither created nor destroyed, but are simply transferred from one material to another. – They have to go somewhere – They can’t just disappear altogether

Electricity - electrons moving through a metal wire.

Measures of Electricity • Voltage • Current • Resistance • Power

• NEED Current SQ 3 R 16. 2

Things you should already know or be able to do… • Differentiate between kinetic and potential energy and analyze situations where kinetic energy is converted to potential energy and vice versa. (6)

Learning Target: • I can define Voltage.

Voltage Potential Energy

Gravity Analogy… • When gravity does work on an object to move it in the direction of the gravitational field, then the object loses potential energy. – An object falls because Gravity does work upon it – Potential Energy decreases as it falls

Gravity Analogy… • Energy would be required to move an object against its gravitational field. – A stationary object would not naturally move against the field and gain potential energy. • Energy (in the form of work) would have to be imparted to the object by an external force in order for it to gain this height and the corresponding potential energy.

Gravity to Electricity • Objects naturally move from high potential energy to low potential energy under the influence of the field force. • Work must be done by an external force to move an object against nature – from low potential energy to high potential energy. • The Potential Energy gained by doing the work is now stored and can be used in the future.

Gravity to Electricity • In a similar manner, to move a charge in an electric field against its natural direction of motion would require work. • The exertion of work by an external force would in turn add potential energy to the object.

Electric Potential Energy Like Charges: The little negative charge does not want to move from point A to point B, so it will require work to move it there. Moving it there will increase it’s Potential Energy. Once it is there, it will have some stored energy available for use The little negative charge does want to move from point B to point A, so NO WORK is required. It will lose Potential Energy.

Electric Potential Energy • Electrical Potential Energy: – The potential energy per charge • The electrical potential energy between two like charges increases as the distance between them decreases (forcing them against natural tendency) • The electric potential energy between two opposite charges increases as the distance between them increases (forcing them against natural tendency)

Electric Potential Energy Like Charges Opposite Charges

Electric Potential Energy Moving a charge against it’s natural tendency increases the potential energy and the charges ability to do work. The stronger the electric field the harder it is to move, the more potential energy gained, the more work it can do. The bigger the charge being moved, the more potential energy gained, the more work it can do.

Electric Potential Energy • Within the cells of the battery, there is an electric field established between the two terminals • The movement of a negative test charge through the cells from the positive terminal to the negative terminal would require work, thus increasing the potential energy

Electric Potential Energy • The movement of negative charge through the wires from the negative terminal to the positive terminal would occur naturally and would not require work. • The charge would lose potential energy as moves through the external circuit from the negative terminal to the positive terminal.

Electric Potential Energy with electricity, we usually talk in terms of • Potential Difference: – Potential Energy at Pt. A minus Potential Energy at Pt. B – Between any two points, the work that must be done against electric forces to move a unit charge from one point to the other. – Work done against nature to put charges in a position to do work. – Similar to the work that must be done to raise an object from one height to another

Potential Difference • Potential Difference is the work required to move +1 C of charge from one terminal through the device to the other terminals (Not through something attached to the device) • Unit is the volt, V 1 volt = 1 Joule/Coulomb (Joule is unit for Energy & Work) • Potential Difference is often called Voltage

Voltage/Potential Difference

Voltage

Voltage (V) - Batteries • Inside a battery a chemical reaction frees up electrons. • Electrons collect on the negative terminal of the battery. • If you connect a wire between the negative and positive terminals, the electrons will flow from the negative to the positive terminal as fast as they can • The speed of electron production by this chemical reaction controls how many electrons can flow between the terminals. • Unless electrons are flowing from the negative to the positive terminal, the chemical reaction does not take place. Once you connect a wire, the reaction starts.

Potential Difference Simple Battery Example showing electrons flowing in a simple circuit • http: //phet. colorado. edu/en/simulation/batte ry-resistor-circuit

Voltage (V) - House Putting it into perspective… • Voltage is similar to water pressure – Most outlets in your house are 120 Volts. • Like the force of a short waterfall. – Your washer and dryer are probably 240 Volts. • Like the forces of a tall waterfall. • More Potential Difference = More Volts = more ability to do Work

Practice: • Which of the following is the definition for voltage? A. The potential difference between two terminals. B. The rate at which charges move through a conductor. C. The rate at which charges move through an insulator. D. The strength of an electric field.

Learning Target: • I can define Current.

CURRENT • Electricity is basically the movement of electrons

Current • Current – rate at which charges move in a conductor – Charges move to a position of lower potential energy – When this happens an electric current is produced – Current is abbreviated with an “I” • Unit of current is the “Ampere” or Amps, A • 1 A = 1 Coulomb of Electrons / Second

Current, I • Using our waterfall analogy… • Current is the amount of water flowing over the waterfall every second High Current Niagara's American Falls, 2010 Low Current Niagara's American Falls, 1969

Current, I Which has greater current? • River: – A lot of water moving relatively slow H W ? Y • Hose – Less water moving faster

Current • Direct Current, DC: Charges always move from one terminal to the other in the same direction. – Ex. Battery • Alternating Current, AC: An electric current that changes direction at regular intervals. – electrons are moved first in one direction and then in the opposite direction – Ex. Electricity in your home

Current • How do lights come on instantly when I flick the switch? • You don’t have to wait for 1 electron to make a complete circuit. There are electrons “waiting” all along the wire. Each electron pushes the one ahead of it, so as soon as the first electron starts to move, the last electron in the wire moves into the light bulb.

Voltage and Current “Volts give jolts… but current can kill. ” It’s like shooting a spitball with a straw vs. without a straw… same amount of force, different results

Voltage and Current – Amps measure how much water comes out of a hose. – Volts measure how hard the water comes out of a hose. – A little bit of electricity coming out really hard won’t kill you – A lot of electricity coming out (even softly) can kill you

Things you should already know or be able to do… • Energy can be transformed within a system or transferred to other systems or the environment. – Electricity flowing through wires generates heat (thermal energy). (4)

Learning Target: • I can define Resistance.

RESISTANCE • Resistance works AGAINST the current

Resistance – Ohms • Resistance, R: – Caused by internal friction – Slows the movement of charges through a conducting material – Unit of measure is the ohm (Ω) Recall… Friction results in Heat

Resistance – Ohms • In our Waterfall Analogy it is anything that would slow down the current or reduce the force… like rocks in the river More friction equals more resistance

Water Hose Example Electricity in a Wire is a lot like Water in a Hose • Voltage is how much pressure is applied to push the water through the hose • Current is how fast the water flows through the hose • Resistance is the friction in the hose

Resistance • Amount of Resistance can Vary: In our water hose example, changing the following will change the amount of Resistance – Diameter of hose – Length of hose – Material (changes the amount of friction) The Same would be true for a WIRE • http: //phet. colorado. edu/sims/resistance-in-a -wire/resistance-in-a-wire_en. html

What Influences Resistance in a wire? • Material of wire – aluminum and copper have low resistance • Thickness – the thicker the wire the lower the resistance • Length – shorter wire has lower resistance • Temperature – lower temperature has lower resistance

Resistance • Resistance is a good thing because it reduces the actual volts something gets Just like • Resistor: a dam – Special type of conductor used to control current

Resistance • Resistance is a good thing As electrons move through the filament in a lightbulb, they bump into metal atoms. Due to the collisions, the metal heats up and starts to glow. The metal which makes up a light bulb filament has a high electrical resistance. This causes light and heat to be given off.

Resistance • Resistance can be a bad thing… • Energy can be lost as electricity travels a long distance… we’ll talk more about this in the next unit

Practice: • Voltage is to current as _____. A. B. C. D. volt is to amp volt is to ohm volt is to coulomb volt is to watt • Current is to resistance as _____. A. B. C. D. amp is to volt amp is to ohm amp is to coulomb amp is to watt

• NEED Battery, Voltage, Current, Resistance Definitions WS

Things you should already know or be able to do… • Construct a simple electrical circuit using wires, batteries and light bulbs. (4)

Learning Target: • I can describe the relationships between current, voltage, and resistance.

Current, Voltage & Resistance • Pressure in the hose (V), rate the water flows through the hose (I) and the type of hose (R) are all related. – If you change one, it affects the others The relationship is known as Ohm’s Law… Voltage = Current x Resistance V=Ix. R

Ohm’s Law Visual: Relationship between V, I and R • http: //phet. colorado. edu/sims/ohmslaw/ohms-law_en. html

Learning Target: • I can use Ohm's Law to calculate current, voltage, and resistance using correct units.

Ohm’s Law

Practice: • There is a potential difference of 12 volts across a resistor with 0. 50 amps of current in it. The resistance of the resistor is _____. A. B. C. D. 0. 5 ohms 6 ohms 12 ohms 24 ohms

Practice: • If there is a current of 6 amps flowing through a 3 ohm resistor, what is the potential difference in the circuit? A. B. C. D. 0. 5 volts 2 volts 9 volts 18 volts

Practice: • If a circuit has a potential difference of 120 volts and a resistance of 10 ohms, what is the current that flows through the circuit? A. B. C. D. 0. 08 amps 1200 amps

Practice: • A bunch of science students get together every Friday night for a science party. Last Friday, they watched a couple of episodes of Bill Nye the Science Guy. They used a TV requiring 2. 00 amps and a DVD player requiring 0. 50 amps. Assume electricity costs $0. 10 per k. Wh and they used 120 V outlets. • What is the resistance of the TV? A. B. C. D. 12 ohms 60 ohms 240 ohms 1200 ohms

• NEED Ohm’s Law WS

Practice: Ohms 4 15 2 9 6 Volts 100 150 30 45 48 Amps 25 10 15 5 8

Things you should already know or be able to do… • Demonstrate how an electric current can produce a magnetic force. For example: Construct an electromagnet to pick up paperclips. (4)

Learning Target: • I can explain how electric current and magnetic force interact to produce mechanical energy.

Electricity and Magnetism – how are they related? When an electric current passes through a wire a magnetic field is formed. The strength of the magnetic field depends on how much current is in the wire. Magnetic Field of a Current-Carrying Wire The direction of the magnetic field depends on the direction of current in the wire.

The Right-Hand Rule The direction of the magnetic field depends on • The thumb points in the direction of current in direction of the current. the wire. • The fingertips point in the direction of the magnetic If you hold a wire in your field. right hand point your thumb in the direction of • The magnetic field runs the positive current, the counterclockwise. direction that your fingers curl is the direction of the magnetic field.

What is an electromagnet? • When an electric current is passed through a coil of wire you create a solenoid. − Each loop of wire adds to the strength of the magnetic field of any neighboring loops. − More loops or more current can create a stronger magnetic field. • When the wire is coiled around a metal core, a very strong magnetic field is produced. This is called an electromagnet. An iron core inserted into a solenoid makes it a strong electromagnet

Electricity & Magnetism • Permanent magnets and electromagnets work together to make electric motors and generators. • The secret is in the ability of an electromagnet to reverse its north and south poles.

Generating Electricity • Direct Current, DC: Charges always move from one terminal to the other in the same direction. • Alternating Current, AC: – An electric current that changes direction at regular intervals. – electrons are moved first in one direction and then in the opposite direction

Direct Current Alternating Current http: //www. pbs. org/wgbh/amex/edison/sfeature/acdc. html

Electromagnetic Devices • Electric motor: a device that converts electrical energy to mechanical energy

Electricity & Magnetism • Around the edge of a disk are several magnets with alternating north and south poles facing out.

Electricity & Magnetism • To make the disk spin, you bring a permanent magnet close to its edge. • The free magnet attracts one of the magnets in the disk (B) and repels the one ahead of it (A) • If you flip the magnet in your hand it will now repel the one it is by (B) and attract the next one (C)

Electricity & Magnetism • In a working electric motor, an electromagnet replaces the magnet you reversed with your fingers. • By changing the direction of current, the electromagnet switches its poles to make the rotor keep turning.

What are electric motors? An electric motor is a device which changes electrical energy into mechanical energy. The trick Is getting the current to change direction

Electric Motor – commutator: a device used to make the current change direction every time the flat coil makes a half revolution. – brushes: devices that connect the wires to the commutator

Trace the path of the Current Clockwise Counter-Clockwise

How does an electric motor work?

Simple as that!!

Another Example of an Electric Motor I I

Another Example of an Electric Motor Rotor or armature (the rotating piece of the motor) I I

Another Example of an Electric Motor Which induces this Magnetic Field, Bcoil Follow the wires and find this direction of current at this instant To align the Magnetic Fields, a CW torque is created. In this position, the torque is maximum I Bext Bcoil τ Rotor or armature (the rotating piece of the motor) I I I Coils (or bar magnets) are used to create the external magnetic field, Bext

Another Example of an Electric Motor The rotor rotates B In this position, the angle between Bcoil and Bext has decreased, so the torque has decreased I Bext co il I τ I I Bext

Another Example of an Electric Motor The rotor continues to rotate I τ=0 In this position, the B-fields are aligned and the torque is zero Bcoil Bext I Bext

Another Example of an Electric Motor Inducing a B-field in this direction B co il Momentum carries the rotor further around I Bext I τ Follow the wires in this position and find that the current in the coils has changed direction I And so the torque continues to be clockwise.

Another Example of an Electric Motor The rotor rotates to this position, which is 180º from where it started. Since the current and Bcoil have switched directions, it is essentially the same configuration as it was at the start. B coil And so, the process repeats… I τ I I Bext

Electric Motor All you need to do now is attach a shaft to the end of the rotating commutator and you can use the motor to do work. (Ex. Like a shaft leading to a propeller that flies a model airplane)

Same concept used on Speakers When the direction of current in the coil of wire changes, the cone attached to the coil moves producing sound waves

Electricity & Magnetism We have seen how electricity can produce a magnetic field, The opposite is also true… a magnetic field can also produce electricity! It is known as Faraday’s Law: An electric current can be produced in a circuit by a changing magnetic field The process is known as electromagnetic induction

Things you should already know or be able to do… • Energy can be transformed within a system or transferred to other systems or the environment. – Trace the changes of energy forms, including thermal, electrical, chemical, mechanical or others as energy is used in devices. (6)

Generating Electricity • Generator: A machine that converts mechanical energy into electrical energy by electromagnetic induction. – This is the opposite of what an electric motor does – http: //phet. colorado. edu/ne w/simulations/sims. php? sim =Generator – Show pick-up coil and generator

Generating Electricity • In a Generator… −the bar magnet is replaced by an electromagnet −it is the electromagnet that spins around a fixed magnet The electromagnet in a generator is rotated by some outside force of mechanical energy. In this setup, a student can rotate a crank to turn the electromagnet

It’s the opposite of a motor… Instead of the current changing direction to flip the magnetic alignment Continuously reversing the magnetic alignment creates an alternating current (electrons move one way then the other)

Practice: • A magnetic field can be produced by _____. A. B. C. D. Moving electric charges Spinning protons Ion transfers A series of resistors

Practice: • An electric motor and a generator are different in that _____. A. Electric motors transfer mechanical energy into electric energy, generators do the opposite B. Generators transfer mechanical energy into electric energy, electric motors do the opposite C. Electric motors rely on chemical reactions, generators do not. D. Generators rely on chemical reactions, electric motors do not.

• NEED Electric Motor & Generator WS

Power –Watts (W) • Recall from last term… – Power – rate that work is done at – Units are Watts • The higher the Watts, the higher the energy output per unit of time.

Power - Electricity • Power = work/unit time • P=vxi = • Unit of measure is the Watt (W) • 1 W = 1 J/sec

Relating these concepts in equations. • Power (Watts) = Volts x Amps • Resistance (Ohms) = P=Vx. I R= (I stands for current)

Lightning

What causes lightning? • Lightning is actually just static electricity on a much larger scale. • The rubbing is caused by air moving around • In thunderclouds bottom is usually negative and top is positive.

Thunder • When the lightning flash happens it heats the air to a temperature 5 times hotter than the surface of the sun. • This causes nearby air to expand vibrate forming the sound we hear as thunder.

Interesting facts • Lightning bolts can travel at speeds of up to 60, 000 miles per second. • Every second around 100 bolts of lightning strike the Earth. • One lightning bolt has enough electricity to power 200, 000 homes. • You are more likely to be struck by lightning than be eaten by a shark.

Some myths • Lightning never strikes in the same place twice. • False, the Empire State Building is reportedly struck 100 times a year. • Wearing rubber shoes will protect me in a thunder storm. • False, Lighting is too powerful to be stopped by half an inch of rubber or several hundred feet of rubber for that matter.

Lightning Video

What are batteries? Batteries are composed of a chemical substance which can generate voltage which can be used in a circuit. There are two kinds of batteries: dry cell and wet cell batteries. Below is an example of a dry cell. The zinc container of the dry cell contains a moist chemical paste surrounding a carbon rod suspended in the middle.

Wet cell batteries are most commonly associated with automobile batteries. A wet cell contains two connected plates made of different metals or metal compounds in a conducting solution. Most car batteries have a series of six cells, each containing lead and lead oxide in a sulfuric acid solution.

What are electric circuits? Circuits typically contain a voltage source, a wire conductor, and one or more devices which use the electrical energy. What is a series circuit? A series circuit is one which provides a single pathway for the current to flow. If the circuit breaks, all devices using the circuit will fail.

What is a parallel circuit? A parallel circuit has multiple pathways for the current to flow. If the circuit is broken the current may pass through other pathways and other devices will continue to work.

What is the difference between an open circuit and a closed circuit? A closed circuit is one in which the pathway of the electrical current is complete and unbroken. An open circuit is one in which the pathway of the electrical current is broken. A switch is a device in the circuit in which the circuit can be closed (turned on) or open (turned off).

How is household wiring arranged? Most household wiring is logically designed with a combination of parallel 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 which will open

How is Electrical Power calculated? 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 in the previous module – the watt (W) Example Problem: How much power is used in a circuit which is 110 volts and has a current of 1. 36 amps? P=IV Power = (1. 36 amps) (110 V) = 150 W

How is electrical energy determined? Electrical energy is a measure of the amount of power used and the time of use. Electrical energy is the product of the power and the time. Example problem: E = P X time P=IV P = (2 A) (120 V) = 240 W E = (240 W) (4 h) = 960 Wh = 0. 96 k. Wh

What is an electromagnet? • Electromagnet – a magnet made from a current bearing coil of wire wrapped around an iron or steel core.

What is a generator? • Generator – a machine that changes mechanical energy to electrical energy • Usually use moving magnets to create currents in coils of wire.

What is a motor? • Motor – a device that changes electrical energy to mechanical energy that can do work

E. Light Bulbs 1. Incandescent a. Have a tiny filament that resists the flow of electrons. b. The filament gets hot and glows to produce light. c. Very hot and inefficient.

2. Fluorescent a. Filled with gas and coated with phosphor. b. Electricity excites the gas making it give off U-V rays. c. Phosphor absorbs U-V rays and glows to make light. d. Very cool, efficient, and last a long time.

What is a galvanometer? A galvanometer is an electromagnet that interacts with a permanent magnet. The stronger the electric current passing through the electromagnet, the more is interacts with the permanent magnet. Galvanometers are used as gauges in cars and many other applications. The greater the current passing through the wires, the stronger the galvanometer interacts with the permanent magnet.

What makes something magnetic? • Moving charges cause magnetism. – Negatively charged electrons moving around the nuclei of atoms make magnetic fields. – Atomic nuclei also have magnetic fields because protons move within the nucleus. – Each electron has a property called electron spin, which also produces a tiny magnetic field. • The magnetism of the uncanceled fields in certain materials combines to make the materials magnetic overall.