Physical Science Chapter’s 20 and 21

Think about it  How are lighting and static cling on your clothes related? Movement of Electric Charges!

What is an electric charge? Electric charge- a property that causes subatomic particles (protons and electrons) to attract or repel each other

What creates a charge? An excess or shortage of electrons produces a net electric charge. Ex. Rubbing a balloon on your head. The balloon will become negatively charged and it will attract positively charged bits of paper.

How are charges attracted or repelled? Positive and negative charges attract. Like charges repel Ex. Think about the north and south ends of a magnet

How do charges affect other charges that are close? Electric charges affect other charges within their electric fields. The strength of an electric field depends on the amount of charge that produces the field and on the distance from the charge.

Static electricity and charging Static electricity is the study of the behavior of electric charges Net charges can build up in several ways Charge can be transferred by friction, by contact and by induction.

Electric Circuits An electric circuit is a complex path through which a charge can flow Circuit diagrams use symbols to represent parts of a circuit, including a source of electrical energy and devices that are run by the electrical energy Ex. Wiring a house or a car

Lab Safety Don’t attach the alligator clips to anything other than the battery or bulb Don‘t lick the bulb or the battery- eww. Be careful, the bulbs ARE glass, and if you squeeze them too tightly they will break… It’s ok if something breaks or doesn’t work, just let me know and I will help you. * Try a few times before you call me over.

Closed and Open Circuits On a circuit diagram switches indicate where a circuit can be opened. If a switch is open the circuit is not a complete loop and the current stops = OPEN CIRCUIT If a switch is closed the circuit is complete and the charge can flow = CLOSED CIRCUIT

Series Circuit In this type of circuit charge has only one path through which it can flow. If one element stops functioning in a series circuit, none of the elements can operate. Ex. Christmas lights

Parallel Circuit A parallel circuit is an electric circuit with two or more paths through which charges can flow. If one element stops functioning in a parallel circuit, the rest of the elements still can operate.

Conductors and Insulators Conductor- material that charges can flow through easily Insulator- material that charges can not flow through easily Ex. Wires – inside is copper conductor, outside is rubber insulator

Resistance Opposition to the flow of charges Resistance is measured in Ohms Ex. Thick milkshake = thick straw : resistance is lower if you make a wire thicker. More electrons can flow through a thicker wire  Resistance is affected by a materials thickness, length and temperature

What is a superconductor? A material that has almost zero resistance when cooled to low temperatures.

Voltage Related to potential difference Think about potential energy- a battery is a source of potential energy Charges flow spontaneously from a higher to lower potential energy. (Think about gravity) Potential difference is measured in joules per coulomb or VOLTS. Potential difference is also called VOLTAGE!

Charging by Contact Ex. A Van de Graaff generator- makes your hair stand on end! Charge is transferred by contact. When you touch the generator you acquire a charge large enough to make your hair stand on end!

Charging by Induction Ex. Touching a doorknob after walking across carpet. Use of an electroscope!!! Next slide  You picked up extra electrons from the carpet-therefore your hand is negatively charged. Your electrons repel the electrons in the doorknob leaving it positively charged –OUCH! Induction- a transfer of charge without contact between materials

What is static discharge? Ex. The static shock from the last example! –OUCH! Static discharge occurs when a pathway through which charges can move forms suddenly. Ex. When you make contact with the doorknob your hand becomes the pathway!

Van Der Graaf Generator Demos Should a person touch 200,000 volts? Big Sparks Little Sparks How Does a Van Der Graaf Work?

Electricity Review (To Be Turned-in ) Electricity Questions 1) What creates a charge? 2) How does charging by friction work? Explain. 3) Give an example of charging by contact. 4) How does charging by induction work? Explain. 5) Current is the flow of electricity- give the two types of current. How are they different? 6)What is resistance and how is it measured? Circuit Questions 7) Draw a series circuit with 3 light bulbs. 8) Draw a parallel circuit with 4 light bulbs. 9) How are open and closed circuits different?

Bill Nye!! Bill Nye- Electric Circuits

Electric Current A continuous flow of electric charge Measured in amps Two types AC – alternating current DC – direct current

Direct current Charge is flowing in one direction

Alternating current Flow of electric charge that regularly reverses direction

Ohms Law V = voltage I = current R = resistance V = I x R or I = V/R V = voltage I = current R = resistance What is the voltage if the resistance is 3 ohms and the current is 3 amps? V = I x R  3 amps x 3 ohms = 9 volts

Ohm’s Law Ohm's Law defines the relationships between (P) power, (V) voltage, (I) current, and (R) resistance. One ohm is the resistance value through which one volt will maintain a current of one ampere. ( I ) Current is what flows on a wire or conductor like water flowing down a river. Current is measured in (A) amperes or amps.

Ohm’s Law ( V ) Voltage is the difference in electrical potential between two points in a circuit. It's the push or pressure behind current flow through a circuit, and is measured in (V) volts.

Ohm’s Law ( R ) Resistance determines how much current will flow through a component. Resistors are used to control voltage and current levels. A very high resistance allows a small amount of current to flow. A very low resistance allows a large amount of current to flow. Resistance is measured in ohms.

Calculating Power ( P ) Power is the amount of current times the voltage level at a given point measured in wattage or watts. Formula for Power: Power = Volts x Current P = V x I

Magnetism Law of Magnets- opposites attract, like repel Pass around the magnets, hold both north ends together and then a north and a south end Do you feel the magnetic force? Keep these away from your cell phone!!

Magnetism Magnetic force- force one magnet exerts on another Acts over a certain distance. Slide the magnet close to the paper clip, notice how close it has to be in order for the clip to jump towards the magnet.

Magnetism Magnets have two poles Magnetic fields are strongest around the poles Watch the demo on the projector 

Magnetism Magnetic Domain- area with a large # of atoms aligned in magnetic fields

Magnetism IF a material is magnetic the domains are aligned IF a material is not magnetic then domains are not aligned Add the drawing on the board into your notes

Magnetism Ways to break a magnet: Heat it Hit it Drop it Why do you think this would cause a magnet to not be magnetic anymore?

Electricity and Magnetism Both are part of electromagnetic force Pass the magnetic over the compass, what happened? Why?

Three Parts of an Electromagnet Coil, Core, Current An electric current creates a magnetic field A moving magnetic field induces an electric current

Important! Electric Motors convert a moving electrial current into a magnetic field Generators convert a moving magnetic field in an electric current How to make an electromagnet- COIL, CORE , CURRENT How to build a simple generator