Chapter 17: Introduction to Electricity Material on Final Exam

Section 17.1: Electric charge and Static Electricity Objectives Describe how charged objects interact by using the law of electric charges. Describe three ways in which an object can become charged. Compare conductors with insulators.

Section 17.1: Electric charge and Static Electricity Electrical Charge Atoms are made of three parts Protons Neutrons Electrons Focus on electrons

Section 17.1: Electric charge and Static Electricity Charges Exert Forces Three charge options +, -, Ø Charges exert forces Law of Electrical charges states that like charges repel and opposite charges attract

Section 17.1: Electric charge and Static Electricity What is happening in A? B? C?

Section 17.1: Electric charge and Static Electricity PROCESS BOX In the space below, explain the law of electrical charges in your own words. You need at least 2 lines. Stamp Spot!

Section 17.1: Electric charge and Static Electricity Electrical Force and Electrical Fields Electrical forces are forces of attraction or repulsion on a charged particle that is due to an electric field Two factors Charge size Charge distance

Section 17.1: Electric charge and Static Electricity

Section 17.1: Electric charge and Static Electricity An electrical field is the space around a charged object in which another charged object experiences an electrical force

Section 17.1: Electric charge and Static Electricity Charge it! How to get a charge? Change # or position of electrons! 3 ways Friction Conduction Induction

Section 17.1: Electric charge and Static Electricity Friction Electrons are “wiped” from one source to another Creates charge

Section 17.1: Electric charge and Static Electricity Conduction A charged substance comes in direct contact with another substance Creates charge by transfer

Section 17.1: Electric charge and Static Electricity Induction A charged substance comes indirectly charges another object Creates charge

Section 17.1: Electric charge and Static Electricity Conservation of charge No charges are created or destroyed through these processes

Section 17.1: Electric charge and Static Electricity PROCESS BOX In the space below, explain how we can charge an item if we cannot create or destroy charge. You need at least 2 lines. Stamp Spot!

Section 17.1: Electric charge and Static Electricity Detecting Charge An electroscope is a device that detects charge As charge is applied, moves charge to metal pieces and separates them

Section 17.1: Electric charge and Static Electricity Conductors An electrical conductor is a material in which charges can move freely Electrons are free-moving Copper, Aluminum, Magnesium

Section 17.1: Electric charge and Static Electricity Insulator An electrical insulator is a material in which charges cannot move freely Electrons are “locked in” and cannot move Plastic, rubber, glass, wood, air

Section 17.1: Electric charge and Static Electricity PROCESS BOX In the space below, explain why it is important to have both conductors and insulators in everyday life. You need at least 2 lines. Stamp Spot!

Section 17.1: Electric charge and Static Electricity Static electricity is an electric charged produced by friction or induction Called static no change Item builds up charge and keeps it

Section 17.1: Electric charge and Static Electricity Electric Discharge Charges eventually leave Electric Discharge is the release of electricity stored in a source Can be slowly Laundry Can be quick Door knob, car door Lightning

Lightning

Section 17.1: Electric charge and Static Electricity Objectives Describe how charged objects interact by using the law of electric charges. Describe three ways in which an object can become charged. Compare conductors with insulators.

Section 17.2: Electric current and Electrical Energy Objectives Describe electric current. Describe voltage and its relationship to electric current. Describe resistance and its relationship to electric current.

Section 17.2: Electric current and Electrical Energy Energy of electrical charges

Section 17.2: Electric current and Electrical Energy Electric current is the rate at which charges pass through a given point If we INCREASE current, we INCREASE the number of charges per second Units: Amperes Amps (A) Calculations: I

Section 17.2: Electric current and Electrical Energy Making Charges move Very fast relay race of charges Electrons move in field to destination

Section 17.2: Electric current and Electrical Energy Current types Alternating Current (AC) Direct Current (DC)

Section 17.2: Electric current and Electrical Energy Alternating Current AC Charges move back and forth Ex: outlets Direct Current DC All charges flow in same direction EX: batteries

Section 17.2: Electric current and Electrical Energy Voltage Voltage is the potential difference between two points The greater the voltage, the greater the current Units: Volts (V) Calculations: V

Section 17.2: Electric current and Electrical Energy Resistance Resistance is the opposition presented to the current by a material or device “Electrical friction” The greater the resistance, the less the current Units: Ohms (Ω) Calculations: R

Section 17.2: Electric current and Electrical Energy Generating Electrical Energy A cell is a device that produces an electric current by converting chemical or radiant energy into electrical energy Parts of a cell Electrolytes—chemical that allows charges to flow Electrode—part of the cell where charges enter and exit

Cell Setup

Section 17.2: Electric current and Electrical Energy Objectives Describe electric current. Describe voltage and its relationship to electric current. Describe resistance and its relationship to electric current.

Section 17.3 & 17.4: Electric Circuits and Calculations Objectives Use Ohm’s law to calculate voltage, current, and resistance. Calculate electric power. Determine the electrical energy used by a device. Name the three essential parts of a circuit. Compare series circuits with parallel circuits.

Section 17.3 & 17.4: Electric Circuits and Calculations Ohm’s Law Georg Ohm (1789-1854) first determined the relationship between current, voltage and resistance. According to Ohm’s Law, the voltage in a circuit equals the product of the current and the resistance.

Section 17.3 & 17.4: Electric Circuits and Calculations Formula Voltage – SI unit Volts Current – SI unit Amps Resistance – SI unit Ohm V = IR V I R

Section 17.3 & 17.4: Electric Circuits and Calculations Math Practice What is the voltage if the current is 4 amps and the resistance is 10 ohms? You try! Find the voltage if the current is 0.2 A and the resistance is 2 ohms. I I R R V = IR V = 4 x 10 V = 40 Volts V = IR V = 0.2 x 2 V = 0.4 Volts

Section 17.3 & 17.4: Electric Circuits and Calculations Math Practice The resistance of an object is 4 ohms. If the current in the object is 9 A, what voltage must be used. You try! An object has the resistance of 20 ohms. Calculate the voltage needed to produce a current of 0.5 A. R R I I V = IR V = 0.5 x 20 V = 10 Volts V = IR V = 4 x 9 V = 36 Volts

Section 17.3 & 17.4: Electric Circuits and Calculations Electric Power Electric Power is the rate at which electrical energy is converted into other forms of energy Where the “wattage” of our lights come from!

Section 17.3 & 17.4: Electric Circuits and Calculations Formula Power – SI unit Watts Voltage– SI unit Volts Current – SI unit Amps P = VI P V I

Section 17.3 & 17.4: Electric Circuits and Calculations Math Practice A computer monitor draws 1.2A at a voltage of 120V. What is the power rating of the monitor? You try! What voltage would a light bulb have if the current is 0.5A and the power is 60W? I V I P V = P I V = 60 0.5 V = 120 Volts P = IV P = 1.2 x 120 P = 144 Watts

Section 17.3 & 17.4: Electric Circuits and Calculations Electric Energy The amount of electrical energy depends on the power of the electrical devices and the length of time that those devices are on

Section 17.3 & 17.4: Electric Circuits and Calculations Formula Energy – SI unit Joules Power– SI unit Watts Time – SI unit seconds E = P x t E P t

Section 17.3 & 17.4: Electric Circuits and Calculations Math Practice How much energy is used if a 50W appliance is run for 5 seconds? You try! How much energy will be needed for a 200W appliance to run for 10 seconds? P P T T E = PT E = 200 x 10 E = 2000 Joules E = PT E = 50 x 5 E = 250 Joules

Section 17.3 & 17.4: Electric Circuits and Calculations Math Practice What is the power of an appliance that uses 200,000 J of energy to run for 1000 seconds? You try! An appliance uses 5000J of energy to run for 4 seconds. What is the power? E E T T P = E T P = 200,000 1000 P = 200 Watts P = E T P = 5,000 4 P = 1250 Watts

Section 17.3 & 17.4: Electric Circuits and Calculations Math Practice How long will a 75W appliance run if it needs 150,000J? You try! A 5000J appliance uses 250 W. How long will it run for? E P E P T = E P T = 150,000 75 T = 2000 seconds T = E P T = 5,000 250 T = 20 seconds

20.3—Electric Circuits Electrical cost Power companies usually charge by the kilowatt hour Steps to find cost Find energy: multiply appliance wattage by time (in hours) Convert to kilowatt hours (either ÷ by 1000 or move decimal 3 times to the left) Multiply by the cost from the electrical company Round to two decimal places

20.3—Electric Circuits A 3000 watt air conditioner was used for 24 hours. What is the cost to run it that long if the electric company charges $0.05 per kilowatt-hour?

20.3—Electric Circuits Mr. Edison uses a 100W light bulb for an average of 150 hours per month. PECO charges them $0.15/kWh, what is the cost?

20.3—Electric Circuits I used a 900W coffee pot for 10 minutes to make coffee. If the cost is $0.07/kWh, what would the cost be to run the coffee pot?

Section 17.3 & 17.4: Electric Circuits and Calculations An Electric circuit is a complete path around which charges can flow There are 3 basic parts Energy source Wires (where charge flows) Load (change electrical energy into other forms)

Section 17.3 & 17.4: Electric Circuits and Calculations Series Circuit Series Circuit Series circuit has only one pathway for an electrical charge to flow. If one element stops functioning in series circuit, none of the elements can operate. Example – the wiring in a burglar alarm 1 Pathway

Section 17.3 & 17.4: Electric Circuits and Calculations Parallel Circuit Parallel Circuit Parallel circuit is a electrical circuit with two or more paths through which charges can flow. If one element stops functioning, the others can still operate. Found in most homes and businesses More than 1 path

Section 17.3 & 17.4: Electric Circuits and Calculations PROCESS BOX How are series and parallel circuits similar? How are they different? You need at least 2 lines.

Section 17.3 & 17.4: Electric Circuits and Calculations Household Circuit Safety Circuit breaker is a switch that opens when a current in a circuit is too high. A strip of metal in the breaker warms up, bends, and opens the switch, which puts a gap in the current thus stopping the flow of charges Fuse a thin piece of metal that melts or breaks when the current is too high. Known as “blowing a fuse” Grounding is the transfer of excess charge into the Earth GFCI = Ground fault circuit interrupter

Section 17.3 & 17.4: Electric Circuits and Calculations

Section 17.3 & 17.4: Electric Circuits and Calculations Objectives Use Ohm’s law to calculate voltage, current, and resistance. Calculate electric power. Determine the electrical energy used by a device. Name the three essential parts of a circuit. Compare series circuits with parallel circuits.