SPH3U – Unit #5

SPH3U – Unit #5 Electricity & Magnetism SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Unit Overview • Electric Energy & Circuits • Electric Charge & Electrical Structure of Matter • Electric Potential • Elementary Charge (The Millikan Experiment) • Electric Current • Resistance • Electric Power & Energy • Series Circuits • Parallel Circuits • Complex Circuits • Magnetism • Natural Magnetism • Magnetic Fields • Electromagnetism (RHR#1 & 2) • The Motor Principle (RHR#3) • Electromagnetic Induction • Lenz’s Law • The Generator Effect • Transformers SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Electric Power & Energy • The watt (W) is a unit of power. • Power is the rate at which energy moves or is used. • Since energy is measured in joules, power is measured in joules per second. • One joule per second is equal to one watt. • One watt is a pretty small amount of power. • In everyday use, larger units are more convenient to use. • A kilowatt (kW) is equal to 1,000 watts. SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Reviewing Terms SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Defining Power SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Example #1 • In North America, the standard electric outlet has a potential difference of 120 V. In Europe, it is 240 V. What would be the power output of a 100W – 120 V light bulb if it was connected to a 240 V system? What would happen to the light bulb? SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Practice • Pg. 655#41, 42 • Pg. 658#43-45 SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Another Relationship for Power SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Example #2 • An electric kettle is rated at 1500 W for a 120 V potential difference. • What is the resistance of the heating element of the kettle? • What will be the power output if the potential difference falls to 108V? SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Practice • Pg. 662#46-50 SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Energy Consumption • A seemingly unusual unit for energy is used when talking about electrical energy consumption – The kilowatt-hour (KW-h). • One kilowatt-hour is the energy transformed by 1000 W in one hour (3.6x10^6J). • A typical charge by an energy company for consumed energy is roughly $0.07 per Kw-h. That means that for 7 cents you can buy enough energy to lift 360 kg a vertical distance of more than 1 km! SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Example #3 • A family has its television set on for an average of 4.0 h a day. If the television set is rated at 80 W and energy costs $0.07per Kw-h, how much would it cost to operate the television for 30 days? SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Practice • Pg. 664#51-53 SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Series Circuits • In series circuits, current can only take one path. • The amount of current is the same at all points in a series circuit. SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Resistance in Series • Each resistance in a series circuit adds to the total resistance of the circuit. Rtotal = R1 + R2 + R3... SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Resistance in Series • Light bulbs, resistors, motors, and heaters usually have much greater resistance than wires and batteries. SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Example #1 • How much current flows in a circuit with a 1.5-volt battery and three 1 ohm resistances (bulbs) in series? SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Voltage in a Series Circuit • Each separate resistance creates a voltage drop as the current passes through. • As current flows along a series circuit, each type of resistor transforms some of the electrical energy into another form of energy. • Ohm’s law is used to calculate the voltage drop across each resistor. SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Kirchoff’s Voltage Law SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Parallel Circuits • In parallel circuits the current can take more than one path. • Because there are multiple branches, the current is not the same at all points in a parallel circuit. SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Parallel Circuits • Sometimes these paths are called branches. • The current through a branch is also called the branch current. • When analyzing a parallel circuit, remember that the current always has to go somewhere. • The total current in the circuit is the sum of the currents in all the branches. • At every branch point the current flowing out must equal the current flowing in. • This rule is known as Kirchhoff’s current law. SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Kirchoff’s Current Law SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Voltage & Current in a Parallel Circuit • In a parallel circuit the voltageis the same across each branch because each branch has a low resistance path back to the battery. • The amount of current in each branch in a parallel circuit is notnecessarily the same. • The resistance in each branch determines the current in that branch. SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Example #2 • Two bulbs with different resistances are connected in parallel to batteries with a total voltage of 3 volts. • Calculate the total current supplied by the battery. SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Advantages of Parallel Circuits • Parallel circuits have two big advantages over series circuits: • Each device in the circuit sees the full battery voltage. • Each device in the circuit may be turned off independently without stopping the current flowing to other devices in the circuit. SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Short Circuit • A short circuit is a parallel path in a circuit with zero or very low resistance. • Short circuits can be made accidentally by connecting a wire between two other wires at different voltages. • Short circuits are dangerous because they can draw huge amounts of current. SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Resistance in Parallel Circuits • Adding resistance in parallel provides another path for current, and more current flows. • When more current flows for the same voltage, the total resistance of the circuit decreases. • This happens because every new path in a parallel circuit allows more current to flow for the same voltage. SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Resistance in Parallel Circuits SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Example #3 • A circuit contains a 2 ohm resistor and a 4 ohm resistor in parallel. • Calculate the total resistance of the circuit. SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Analysis of Circuits • All circuits work by manipulating currents and voltages. • The process of circuit analysis means figuring out what the currents and voltages in a circuit are, and also how they are affected by each other. • Three basic laws are the foundation of circuit analysis. SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

The 3 Circuit Laws SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Solving Circuits Problems • Identify what the problem is asking you to find. Assign variables to the unknown quantities. • Make a large clear diagram of the circuit. Label all of the known resistances, currents, and voltages. Use the variables you defined to label the unknowns. • You may need to combine resistances to find the total circuit resistance. Use multiple steps to combine series and parallel resistors. SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Solving Circuits Problems • If you know the total resistance and current, use Ohm’s law as V = IR to calculate voltages or voltage drops. If you know the resistance and voltage, use Ohm’s law as I = V ÷ R to calculate the current. • An unknown resistance can be found using Ohm’s law as R = V ÷ I, if you know the current and the voltage drop through the resistor. • Use Kirchhoff’s current and voltage laws as necessary. SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Example #4 • A bulb with a resistance of 1Ω is to be used in a circuit with a 6-volt battery. The bulb requires 1 amp of current. If the bulb were connected directly to the battery, it would draw 6 amps and burn out instantly. To limit the current, a resistor is added in series with the bulb. What size resistor is needed to make the current 1 amp? SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Combined Circuits • Key Question: • How do we analyze network circuits? SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Combined (Network) Circuits • In many circuits, resistors are connected both in series and in parallel. • Such a circuit is called a network circuit. • There is no single formula for adding resistors in a network circuit. • For very complex circuits, electrical engineers use computer programs that can rapidly solve equations for the circuit using Kirchhoff’s laws. SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

Example #5 • Three bulbs, each with a resistance of 3Ω, are combined in the circuit in the diagram • Three volts are applied to the circuit. • Calculate the current in each of the bulbs. • From your calculations, do you think all three bulbs will be equally bright? SPH3U – Physics 11 University Preparation – Unit 5 – Electricity & Magnetism Created by: Mr. D. Langlois – GECDSB – www.mrlanglois.wordpress.com

SPH3U – Unit #5

SPH3U – Unit #5

Presentation Transcript

Table of Contents – pages iv-v

Table of Contents – pages iii

Table of Contents – pages iv-v

Table of Contents – pages iv-v

Table of Contents – pages iii

Table of Contents – pages iv-v

Unit 1

Table of Contents – pages iv-v

Table of Contents – pages iii

Table of Contents – pages iii

英语（新目标）B

Table of Contents – pages iv-v

Table of Contents – pages iii

Table of Contents – pages iv-v

Table of Contents – pages iv-v

Table of Contents – pages iv-v

TABLE OF CONTENTS

Table of Contents – pages iv-v

Table of Contents – pages iv-v

Table of Contents – pages iv-v

SPH3U – Unit #5

SPH3U – Unit #5

Presentation Transcript

Table of Contents – pages iv-v

Table of Contents – pages iii

Table of Contents – pages iv-v

Table of Contents – pages iv-v

Table of Contents – pages iii

Table of Contents – pages iv-v

Unit 1

Table of Contents – pages iv-v

Table of Contents – pages iii

Table of Contents – pages iii

英语 （新目标）B

Table of Contents – pages iv-v

Table of Contents – pages iii

Table of Contents – pages iv-v

Table of Contents – pages iv-v

Table of Contents – pages iv-v

TABLE OF CONTENTS

Table of Contents – pages iv-v

Table of Contents – pages iv-v

Table of Contents – pages iv-v

英语（新目标）B