Physics 3204 Workbook Unit 2.pdfView Download

40% of the year 3 Tests

3 Sub - Topics

Electrostatics – Test 03  Current Electricity – Test 04 Electromagnetism – Test 05

Page 2 of 79

Lesson 2.01 Intro to Field Theory

Unit 2 - Fields

Fields: A region of 3-D space in which a _____________________ or quantity, such as a ____________________, may be distributed.

Ex: 

Objects with mass set up ______________________ fields which affect other objects with mass.  Objects with electric charges set up _____________________________ fields which affect other objects with charge.

 Objects with magnetic properties set up ____________________________ fields which affect certain bodies. (Magnetic or ferrous materials)

Gravitational Fields: A region of space that affects ________________________.

We use field lines (vectors) to denote the ____________________ and ___________________ of the field.

The direction of a gravitational field is always ___________________________ which creates the field.

Close together field lines represent ____________________ fields, spread out field lines are a weaker field.

__________________ Field (lines close together) Weak Field (lines _______________ apart) __________________ Field (lines parallel)

Assign:

Read p. 524 p. 187 #21,22,24

Imagine dropping a __________________________ at various points around the earth. What direction would the mass take?

We can use ______________________________________________________________ to determine the force between any two masses.

We use a shortcut, g = 9.80 N/kg, and this is the ______________________________________. It shows how strong the field is at a particular point.

Newton's Universal Law of Gravitation says that as you get farther away, the gravitational force decreases, but never

Page 4 of 79

Lesson 2.02 – Static Electricity

Electrostatics: (p. 527)

 The study of electric forces and fields where the charges are ________________________ rest.  Balloons, spray painting, shocks, grounding, carpets, bbq starters are all examples.

Features of the electric field:

It can __________________________________

It can act through a _____________________________ (outer space)

It is ______________________________________ than the gravitational force It acts as an ________________________________________ (more later)

The Atom:

Protons, p+, electrons, e- , and neutrons n. The p+ and n are ____________________ in the nucleus and never move, while the e orbit the nucleus in ________________________________ or shells and are freer to move around. We will represent negative charges as (-) and positive charges as (+).

neutral objects   + objects - objects equal number p+ and e-  deficit of e-  surplus of e

-In their natural state, most objects start off neutral

Protons never move. Electric charge is always caused by a surplus (extra) or deficit of (not enough) e.

Law of Electric Charges:

 - Opposite charges attract each other  - Like charges repel each other

 - Charged objects will sometimes attract neutral ones

Electroscope: (p. 529)

An electroscope is any object that will allow us to detect electric charge. If there is a surplus of charge, the leaves will move apart.

Page 6 of 79

Creation and Transfer of Electric Charge

Since all objects begin neutral, we must have some way of creating a charged object. There are three ways, friction, contact, induction

Charging by Friction:

Rub two neutral objects together e- transfer from one to the other based on their affinity for electrons. Charge is determined by an electrostatic series. (see pg. 530)

*Ex. Fur and ebonite rod. (The total # of e does NOT change, they are just moved around) Draw below.

Charging by Contact:

 - Touch a charged object off an uncharged one.

Charging by Induction:

 - Bring a charged object near, but not touching an uncharged one.  - This causes a local charge distribution.

 - Ground out the uncharged object (ground merely means provide a path for electrons)  - Remove the ground

 - Remove the object

*need to remove the ground FIRST if not excess charge bleeds out

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2. Local Charge Separation

3. Provide a path for the electrons to leave

4. Remove the ground first

Remove the rod last. Otherwise, the object will return back to a having no charge (neutral.)

Ex. How does a balloon that is rubbed against your head gain charge, and then

stick to the wall? Explain with reference to

charging by friction

,

electrostatic

Page 10 of 79

Hwk: Assign. Read p. 527- p. 532

Problems p. 579 #’s 1-6

Page 12 of 79

Lesson 2.03: Electrical Discharge

Electrical Discharge:

An excess of either charge means that the electrons will experience a force of repulsion.

In a lightning strike the charge separation (e removed from p) means that there is a

tremendous force either pushing e out from a negative cloud, or pulling e in to a positive cloud.

If the force is large enough, a discharge will occur across the intervening gap.

The purpose of a lightning rod is not to attract lightning, but rather to prevent the________________ from happening in the first place.

Charge Distribution:

Charge is not uniformly distributed around pointy objects.

In fact, there is no charge inside a hollow charged object, all the charge resides on the surface. This is why you are safe in a car in a lightning storm. All the charge resides on the surface of the car.

Conductors and Insulators:

Conductors are materials that _________the transfer of e through them. Metals such as Cu, Ag, Au

Insulators ___________the flow of e (they do not stop it altogether). Most non - metals.

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Charge is measured in Coulombs (C.) The elementary charge is given by:

_______________________

This charge is the same for electrons and protons, but for e it is negative, and for p it is positive.

Total charge is given by:

Where: Q = N = e =

* Remember that this will give you the total charge, you must determine the sign based on whether you have a surplus or deficit of electrons.

A Coulomb is a massive amount of charge; a lightning strike typically only releases 20 C or so. We will more commonly use microCoulombs (μC) or nanoCoulombs (nC) where:

1.0 μC = __________ 1.0 nC = __________

2.04 - Coulombs Law

Hwk: (in class if finished

early) Read p. 523 - 534

Next Day in class: 

Assign p. 582 # 33- 45

Worksheet #01 -Theory

Page 16 of 79

Coulomb's Law

A law which describes the amount of electric __________between two _____________some

distance away from each other.

A point charge is an extremely small particle which carries a charge. 
(No charge separation or movement)

This is different from a hollow sphere which can carry a charge. (Charge separation and movement possible)

Mathematically:

Where:

F =

k =

Q1 =

Q2 =

r =

F α Q

F α Q

ex:  double Q1 = ________________

 double Q1 and triple Q2 _____________________

Inverse Square Law!

F α 1

r

ex:  double r  = ____________  triple r  = _____________

  triple r and double Q1 =  ________________

Ex 1:  Two point charges of + 1.9 nC are separated by 22.0 cm.   What is the force acting on each one?

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Ex 2:  Three charges are arranged as shown below. Determine:  a)  the net force on B

 b)  the net force on C

 Recall that since force is a vector we need to calculate separate  forces in a FBD and then do a vector diagram.

Ex 3:  Find the net force acting on charge "B" in the diagram below. QA = - 6.2 μC

QB = - 8.8 μC

QC = + 4.1 μC

17.0 cm

23.0 cm

A _B

Page 20 of 79

2.05 - Electric Fields

Warmup: Find the net electric force (magnitude *POP POP*) and direction acting on charge B. QA = - 1.2 x 10 - 6 C

QB = + 3.2 x 10 - 6 C

QC = - 2.2 x 10 - 6 C

Hwk:  Hwk Set # 9 Coulomb's Law

Next Day in Class Worksheet 2

Next

Day in

Class

Worksheet

2

Recall that to draw gravitational field lines we imagined dropping a test mass and drew the lines which represented the path the test mass would take.

Electric Fields:

A region of space which affects _____________.

To draw electric field lines, we imagine dropping a test charge and draw the lines which represent the path a test charge would take.

By convention, test charges are always positive.

Field lines around spheres

 Positive Sphere  Negative Sphere

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Two Objects, Same Charge

Two Objects, Opposite Charge

The Field lines are _____________, meaning that the field is _______________. If you place a charge anywhere within this field it will experience the same force.

Non - Uniform Objects

High Charge concentration means high field strength.

Long Straight Conductors

Page 24 of 79

Let’s compare

Gravity

to

Electrostatics:

Where:

ε⃗ =

___________

F⃗⃗ =

___________

q = ____________

Ex 1: A small foam ball with a charge of + 1.5 x 10-6 _{C experiences a force of 3.0 N [left].}

Ex 2: What force is experienced by a - 6.0 μC charge when placed in an electric field of 6.0 x106 _{N/C [Right]?}

Page 26 of 79

Where:

ε⃗ =

___________

k = ___________

qm = ___________

r = ___________

Ex 4: Find the net electric field strength at point "P" as shown below.  * how many fields act at point "P"?

In Class

Read p. 546 – 556

Do p. 557  #1, #3 a-c, e, #4 ab Do p. 584 #59-66*not for homework, remainder will be finished next day

For Homework

Page 28 of 79

2.01 – Electric Potential

Work-Energy Theorem:

Work and energy are the same thing. The work you do on something W measured in joules (J)

gets converted into Energy E, measured in joules (J).

We can store energy in a charge by doing work on it to separate it from an opposite charge.

In _________________________, as you do work on a mass and move it higher in a gravitational field it stores more energy.

Likewise, as you do work on a charge to move it “higher” in an electric field it also stores more energy. The “levels” you move the charge through are called ______________________.

Gravitational Potential Energy

Electric Potential Energy (Joules)

Total work done to move a charge to that location. Joules (J)

Electric Potential (Voltage, V)

The amount of energy per unit charge required to move that charge (or released from that charge)

Measured in Volts, V.

V = _____________________________ W = _____________________________ q =  ______________________________

V = W

q

Page 30 of 79

So, a 12V car battery provides 12 J of energy to each Coulomb of 
charge in the battery.

Electric Potential

difference

(Voltage, V)

Equipotential Lines

lines which connect points of equal voltage perpendicular to field lines no work is done to move along an equipotential line.

Equipotential Lines in two parallel plates

Page 32 of 79

2.09 – Intro to Current Electricity

Current Electricity

The movement of charged particles (usually electrons) along a path (usually a wire or other conductor)

Note that the speed of the electrons is constant. If you want more electric current, you need more electrons to flow.

Electric Current, I, is defined as the rate of ________________flow over _______________.

Where:  I = ____________________   Q = ____________________   t = ____________________

Ex: A toaster draws 7.0 A of current from a 120V source. How many 
electrons pass through the toaster in 2.0 minutes?

I = Q

t

Direction of Current Flow

Electrons will flow from (-) to (+). This is called ___________________. In industry, conventional current is used.

_____________________flows from (+) to (-). It doesn't affect calculations at all, and for the rest of the year we will use electron current in all diagrams.

Measurement of Electric Current

An _______________is a device to measure large amounts of current flow. Think of it as a bouncer at a bar. It counts charge as it flows past. More charge means higher current.

Page 34 of 79

Connection of an Ammeter

Because Ammeters "count" flow, all the charge must pass them. They must be connected in ________. (only one path)

Also, ammeters cannot interfere with the current they are trying to measure, therefore they must be very good___________.

*Consider the circuits setup below. In which will the ammeter correctly measure the current through R

Symbols you need to know:

Ground Cell Battery

Ammeter Galvanometer Resistor

Voltmeter Lamp Switch

Fuse

Read:   p. 590 - 593

p. 594 # 1-4

Page 36 of 79

2.10 Coulomb Trucks

Electric Potential:

Creating a charge separation allows you to store energy.

A battery (electrochemical cell) is a ____________of voltage. It acts as a __________, pumping electrons full of energy (raising their potential) so that they can transport this energy elsewhere.

Later in the circuit, this energy is transferred to lights, heaters, 
etc. These devices are called____________, or________________.

A battery can be thought of as bridging equipotential lines.

ΔV = W

q

Measuring Potential Difference (Voltage, V)

Device must be connected before and after the load or source to be measured (in parallel) Voltmeters have _____________ resistances

Which of these circuits have the Ammeters and Voltmeters connected correctly to measure the current and 
voltage of R?

Page 38 of 79

Each truck represents a Coulomb of charge (6.25 x 1018 _electrons).

The number of trucks driving past each second is Current (Amperes) The Energy on each truck is measured in Joules. (J)

Supplying Electrical Energy (read p. 598)

Electrochemical cell: Converts _____________ energy into ______________ energy. A group of cells is called a battery.

Piezo-Electricity: Quartz and other crystals can convert _______________energy into _____________energy when they are made to vibrate.

Thermoelectricity: High temperatures will generate a ______________________ across two dissimilar metals. Used in high temperature thermocouples.

Page 40 of 79

Electromagnetic Generators: A spinning ______________in a coil of _________will create electricity. ________________Energy into ________________Energy.

Wind Hydro-electric

Coal, Oil, Natural Gas or Nuclear Generators

Read:  p 594 -

597

  p 597 #

1, 3, 4 

2.11 Ohm’s Law

Resistance

Resistance: The measure of the _______________ to the flow of electricity. Obtained from the ___________ of a V -vs- I graph. The SI unit is the "__________" Ω.

Ohm's Law

"The resistance of a material can be determined from the ratio of the voltage across the resistor to the current flow through the resistor"

Where: R = _________________ V = _________________ I = __________________

Ex:  A voltage of 6.0 V drives a current of 1.0 A through a circuit. 
 What is the resistance of the circuit?

Page 42 of 79

Resistors are called ______________________because the slope of the VI graph is a straight line. These elements are _________________.

Other elements such as _________________and ________________are not linear elements, and you require complex numbers to represent these. These elements are __________________.

Ohmic Non-Ohmic Non-Ohmic

Resistance of a wire

Resistance depends on the ____________of the object, its_______________________, the __________________, and the________________________.

R α L

R α 1

  A

R α 1

  r

Type of material:

The _____________________is a property of the material, much like melting point. Good conductors like copper, silver, and gold, all have ___________ resistivities. To calculate the resistance of a long piece of circular wire we use the equation:

Where: R = _____________________

 = _____________________ L = _____________________ A = _____________________

Page 44 of 79

Ex 1: A wire with a resistivity of 2.8 x 10-8 _{Ωm has a length of 2.0 m and a radius of 1.5 mm.}

What is the resistance of this length of wire?

Ex 2: A wire with a resistance of 50 Ω is stretched from 1.0 m to 3.0 m while its radius is reduced from 1.0 mm to 0.5 mm. What is the new resistance?

HWK:  Read p. 599 - 603

Do p. 621 #23 - 27

2.12 KVL and KCL

Series and Parallel Circuits

Simple Circuit:  A circuit consisting of a ____________________and a __________________.

Series Circuit: Loads are connected one after the other in a single path. ______________flow through a series path must be constant. _______________splits over each load.

Parallel Circuit: Loads are connected side by side in multiple paths. ______________flow splits through each path. ______________drop across each branch is equal.

Page 46 of 79

Complex Circuits:  Contain various connections in both series and parallel.

Kirchhoff’s Current Law (KCL):

The total current flow into a junction point ______________ the total current that flows out of a junction point.

This means that current between two points in series is ________________.

Ex: If you are told that the source provides 9.0 A and that I1 = 6.0 A, what is I2 ?

You can pick a junction point (or node) anywhere, but it is usually placed where wires branch or combine.

R0 _{R2 R}

3 R1

I0 = 9.0 A

I1 = 6.0 A

Kirchhoff’s Voltage Law (KVL):

The total of all electric potential increases in any complete loop in a closed circuit must ___________ the total of all the electric potential decreases in that loop.

This means that voltage drop across parallel branches must be ______________.

Ex 2: If you are told that the source provides 25 V and that V1 = 2.0 V and V3 = 13.0 V, what are

the values for V2 and V4?

A complete loop must start and end at the source.

These rules are based on the laws of conservation of electric charge and conservation of energy

Read  p. 605 - 607

 Homework set #11 KVL and KCL

R1 R2 R3

R4

25 V 2 V

Page 48 of 79

2.13 Resistance in Series and Parallel

Total Resistance in Series

*write equation here

The more resistors you add in series, the ____________ your total resistance becomes.

Total Resistance in Parallel

*write equation here

The more resistors you add in parallel, the _____________your total resistance becomes. This is an issue in household circuits...the more things you plug in, the lower your total resistance, so the

______________your current. (higher load on the circuit)

R1 R2 R3

R1

R3

Total Resistance in Complex Circuits

Complex circuits contain both ______________ and _____________ branches. To determine the equivalent resistance, we need to reduce each branch to a single resistance.

Page 50 of 79

HWK:

 p. 609 #1-3

p. 622 #29-34

Worksheet #2

2.14ircuit Analysis

*Insert workings in on loose leaf

Worksheet #3

Page 52 of 79

2.15 Power in Electric Circuits

Warmup

Calculate the following: V4

R1

I3

Power

The rate at which energy is used or supplied.

Rearranging we get:

P: _________________ I: __________________ V: _________________ Dividing by time we get:

Using Ohm’s law, we can say V = IR and sub this in to obtain two more relations:

Cost of Electricity:

Energy is purchased just like any other commodity.

The unit of energy that we use in physics is the Joule, but this is a very small unit.

For purchasing electricity, we use the unit of a kW.h. 1 kWh is the energy dissipated by a load in one hour with a power rating of 1 kW.

As an example, we pay about 11 cents per kW.h.

Page 54 of 79

Ex: Alyssa is home blow drying her hair. How much does it 
cost if the 1500 W hairdryer runs for 15 minutes at a rate of 
13 cents / kWh?

Assign :  

p. 615 #1-3 omit 2b

p. 617 #1-2 (finish for hwk) p. 623 # 36-40

Then Test

2.18 Intro to Magnetism

Magnetism

Domain Theory:

All large magnets are made up of smaller magnetic regions called________________. The magnetic character of domains comes from the presence of even smaller units called

_______________. Dipoles interact with the neighboring dipoles. If they align with all the poles in one direction, then a larger __________________________is produced.

Materials made of domains that can be readily aligned to create a larger object of magnetic character are called _____________________ materials, such as iron, nickel and cobalt. Naturally occurring magnets are called ______________________.

Page 56 of 79

Law of Magnetic Forces:

Similar magnetic poles ____________ one another. Opposite magnetic poles ______________ one another.

Mapping Magnetic Fields:

Recall how we mapped gravitational and electric fields:

_________________ direction a 1 kg mass would take if placed in the field. _________________ direction a positive charge would take if placed in the field. _________________ direction a north pole would take if placed in the field.

Drawing Magnetic Field lines:

Sketch the magnetic field lines around:  a single bar magnet

 two bar magnets opposite poles/like poles

 horseshoe magnet  the earth

Two Bar Magnets

(like poles)

Two Bar Magnets

(opposite poles)

Page 58 of 79

Earth

Hwk:  Assign read p.628-632

Do p. 663 # 1- 5

2.19 Current Carrying Conductors

Artificial Magnetic Fields - Electromagnetism:

Hans Christian Oersted experimented with current carrying conductors in the early 19th century and discovered one of the most important discoveries of the time. Previously the areas of

electricity and magnetism were thought to be separate, but he found that they were both different sides of the same phenomenon - namely ______________________.

Oersted’s Principle

Charge moving through a straight conductor produces a _____________ magnetic field around the conductor. The field is represented by ________________ rings around the conductor.

Left Hand Rule #1(LHR#1)

: 

Grasp conductor with left hand such that the thumb is pointing in the direction of current flow. The curved fingers point in the direction of the magnetic field.

Page 60 of 79

Does Oersted's Principle help us understand magnetic fields?

Moving charges create magnetic fields, so perhaps the movement of electrons inside a substance creates a magnetic dipole?

Paramagnetic Materials

Electrons are spinning in their orbitals, so any electrons which are _______________create a small magnetic field around the atom.

Paramagnetic substances are _____________ attracted to magnets. ex: oxygen

Diamagnetic Materials

When the ________ of electrons are spinning in _______________directions the magnetic fields will cancel.

These materials are actually ________________by a magnetic field and are called

Diamagnetic.

Many superconductors become diamagnetic at ___________ temperatures.  ex: Yttrium barium copper oxide

Ferromagnetic Materials 

When there are ______________________ electrons and they spin in the ____________ direction, they will tend to align nearby electrons as well.

This produces the ______________ magnetic field observed in ferromagnetic substances. ex: Magnetite

Hwk: Assign reading p. 633 - 635

p. 638 #1

Page 62 of 79

2.20 Electromagnets

Magnetic Field around a coiled conductor (solenoid):

When a straight wire is coiled it forms a _________________. This is also called an

__________________.

Inside and outside the coil, the fields reinforce each other, displaying field lines that resemble a bar magnet. There is a LHR to allow us to find the north pole of this induced magnetic field.

Left Hand Rule #2 (LHR #2) 

Grasp the coil with the left hand such that the fingers curl in the direction of the current. The thumb will point towards the north end of the electromagnet. (see p. 636)

Factors affecting the strength of an electromagnet:

Current in the coil: The _________ the current flow the ____________ the field strength

# of turns in the coil:  More coils means more ________________________

Size of the coil: Smaller diameter coils have ____________ field strength

Type of material in the centre:  More ferromagnetic substances make better centres. This is the measure of the _____________________________________ (μ).

Magnetic Permeability (μ):

The ratio of the magnetic field strength of the electromagnet with core compared to the

electromagnet without the core. The best cores are metals such as soft iron, steel, permalloy (see fig 15.3 p. 637)

Applications of Electromagnets:

Electromagnets are better than permanent magnets because they can be turned off when not needed.

(i) Lifting electromagnets:  Used in junkyards to lift and then drop cars.

Page 64 of 79

(ii) Relay: Used as a way to isolate a high current circuit as a safety precaution.

(iii) Electric bell: a self-switching electromagnet

Assign Read:  p. 635-637

 Do p. 638 #2-4

2.21 The Motor Principle

The Motor Principle

Electromagnets are extremely versatile because they can create a magnetic field that can be varied in force or direction or even shut off. When two different magnets interact, a force of __________________ or _______________________ occurs.

“When two magnetic fields interact they produce a force. If a current-carrying conductor cuts through a uniform magnetic field, it experiences a force directed at 90° to both the direction of charge flow and to the uniform external magnetic field.”

An _____________________ is a device designed to continuously provide a magnetic force in a particular direction.

ElectricKinetic = ___________________ ChemicalKinetic = _________________

Page 66 of 79

Left Hand Rule #3 (LHR #3) The motor principle:

Open the left hand so that the fingers point in the direction of the permanent magnetic field, from north to south. Rotate the hand so that the thumb points in the direction of the electron flow.

The resultant force on the wire will come out of the palm of the hand.

Magnetic Field Strength

 Equation for force exerted on a straight conductor in a permanent magnetic field.

Where: F: _________________________ B: _________________________ I: __________________________ L: __________________________ : ___________________________

Ex:  How much force is exerted on 2.5 m of wire carrying 2.0 A of current through a magnetic field of 5.0 x 10-3 T if the wire is:

  a) perpendicular to the field   b) at an angle of 30° to the field   c) parallel to the field

Page 68 of 79

2.22 Biot’s Law

Biot's Law

 The magnetic field around a straight conductor will be determined by:  (i) current (I)

 (ii) magnetic permeability (μ)

 (iii) perpendicular distance away from wire (r)  Mathematically this is called Biot’s Law:

Where: B: ____________________________ : _____________________________ I: ______________________________ r: ______________________________

What happens if we have two wires? Since Magnetic Field Strength is a vector, we must calculate both fields separately and then use vector addition.

μ is the magnetic permeability of the substance the wires are in; typically air. Ex:  Calculate the net magnetic field (magnitude and direction) at point 'P' below.

1. Diagram

3.  Vector addition (refer back to diagram)

2. Find β1 and β2and do vector addition.

Assign read 639 - 641

do p. 663 #17, 18, 22  (Distance for 22 is 1.0 cm)

 (22 b is wrong...correct answer is doubled) 

 Assign Homework Set #13 Biot’s Law

Page 70 of 79

2.23 Moving Charges in a Magnetic Field

The Unit for Electric Current

Recall that previously the Ampere was defined as 1.0 C per 1.0 s. This is an easy unit to

visualize, but it is very hard to actually measure the flow of charge, because it is moving so fast. The operational definition of the Ampere is based in the interaction of magnetic fields

created by current carrying conductors.

“One Ampere is the current flowing through two parallel conductors, placed 1.0 m apart in air, that exert a force of 2.0 x 10-7 _{N/m on each other for each metre of their length.”}

Magnetic Force on Moving Charges

As we have already seen, a moving charge will create its own______________________. This moving charge need not be bound by a _______________; a stream of electrons will be deflected by a magnet in your television or computer monitor to hit the screen and create an image.

The magnetic force on an individual moving charge is given by:

Where: F: ____________________________ q: ____________________________ v: ____________________________ B: ___________________________

: ___________________________

*note that F, v, and B are all vectors

As with conductors, the force is strongest when the particle is moving ________________, and

zero when it is moving _________________ to the magnetic field. The direction of the deflection can be determined by use of the LHR #3.

Recall that the LHR only applies to _______________ charges, and that the result we obtain must be the __________________ if the charged particles are positives.

Ex1: A magnetic field of strength 0.30 T emerges from the page (represented by the dots). An electron enters the field with a velocity of 6.0 x 106 _{m/s [right].}

 a)  What is the force (magnitude and direction) on this electron?

b)  How would this force change if the moving particle were a proton?

Page 72 of 79

Ex 2: An electron is moving at 5.0 x 107 _{m/s at a distance of 5.0 cm from a long straight}

conductor carrying a current of 35 A.

 What is the magnetic force exerted on the electron when it is moving parallel to the wire as shown below?

Homework Set #14 - Moving

Charges in a Magnetic Field

Read p. 645 - 649

2.24 Moving Charges in Circular Motion

Centripetal Magnetic Force

A particle moving at constant speed in a uniform magnetic field where the field is perpendicular to the particle's velocity will trace a __________________path.

This means that the magnetic force will provide a _______________________to keep the particle in circular motion.

The other alternative is that the particle is not moving perpendicular to the field, and so _________________________to doom. *diagrams below

F Net = F Magnetic

 But for UCM

   F Net = FC

   Therefore:

 qvB = mv2

  r

  Which simplifies to:

Where: r: _________________________ v: _________________________ B: _________________________

Page 74 of 79

Ex 1:  What is the velocity of an alpha particle moving in a circular path of radius 10.0 cm in a plane perpendicular to a 1.7 T magnetic field.

 (The alpha particle has a mass of 6.68 x 10-27 _{kg and a charge of +2e)}

Hwk: Assign read p. 653 - 656,

p. 660 - 661

2.25 Faraday and Lenz’s Law

Induction and Faraday’s Discovery:

“A magnetic field that is moving or changing intensity near a conductor 
causes or induces electron flow in the conductor”

 - Michael Faraday

Moving the magnet in and out continuously causes the current to move back and forth continuously in what is called an ________________________________.

Key ideas from Faraday’s Iron Ring Experiment:

1. The primary coil becomes an _________________ which induces current in the secondary coil 2. Once the magnetic field is established, there is ______________ current induced, until the field collapses.

3. When the field collapses the induced current appears again, just flowing in the ______________ direction.

4. There must be ___________________ movement between the magnetic field and the conductor to induce current flow.

Page 76 of 79

Using LHR #3 to determine the direction of current flow:

As we recall, the electron flow, magnetic field, and force must all be at ___________________ to each other, so we can use the rule to determine the direction of flow in a conductor that is pulled through a permanent magnetic field, as long as we realize that the magnetic force must always oppose the applied force! (The universe hates you)

Ex: Pull wire down through field  Pull wire out through vertical field

Lenz’s Law and Induced Current:

A moving magnet will induce a current in a conductor. But a current (like the one we just induced) will create a magnetic field. How do these two magnetic fields (induced and inducing) interact?

“The Direction of the induced current creates an induced magnetic field that opposes the motion of the inducing magnetic field”

Examples: Sketch Diagram 16.5 p. 672.

Which way will current be induced in these solenoids?

1. Use Lenz’s Law to determine what pole is necessary to oppose the motion of the bar magnet. 2. Use LHR #2 for solenoids to predict the direction of current flow.

Hwk:  Assign read p. 670 - 673

 Do. p. 673 # 1 - 2

Page 78 of 79

2.26 Generating Electricity

Electrical Generators

Faraday's discovery, along with Lenz's Law, allow us to construct a practical device to convert mechanical energy into electrical energy.

This device is called an _____________________.

Generators consist of a __________________, a_________________, and some means of making one of them _____________ relative to the other.

All generators do this...no matter what the fuel source is that powers them.

DC Generators have a device called a ____________________which re-reverses the current flip. The resulting current graphs of both AC and DC generators are shown:

An increase in frequency of the __________________________ (rotor) will increase not just the output frequency of the signal, but also the ___________________ output.

An increase in ____________________________ of armatures (rotors) will give more sinusoids. This is how a real generator deals with the zero voltage issue of a single coil generator.

The generator has a ________________________, T which is the time for one complete rotation. More usually generators are represented by __________________________, f, which is number of rotations per second.

Assign read p. 673 – 675

Magnetism worksheet

This is the end of Unit 2 – Fields. You are now finished 80% of the year. Congrats.