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PHY132S Lecture 13 - EM Lecture 5 - Slide 1

PHY132 – Review for Mid-Term Test

“Examinations are formidable even to the best prepared, for the greatest fool may ask more than the wisest man can answer.”

Charles Caleb Colton, English writer (1780-1832)

“I was thrown out of college for cheating on the metaphysics exam; I looked into the soul of the boy sitting next to me.”Woody Allen, American actor & director (1935- )

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PHY132S Lecture 13 - EM Lecture 5 - Slide 2

PHY132 Mid-Term Test – General Comments

6:10 - 7:30 PM, Tuesday, February 24

It is mandatory that you go to the room assigned to your tutorial group.

Test information and room assignments are on the PHY132 home page via the Portal

You should have no communication device (phone, pager, etc.) within your reach or field of vision during the test.

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PHY132S Lecture 13 - EM Lecture 5 - Slide 3

PHY132 Mid-Term Test –Format Format - similar to PHY131 Mid-Term Test 9 equally weighted multiple-choice questions Each question has 4 or 5 possible answers. Each correct answer will be awarded 7 marks. Blank, incorrect, and multiple answers get 0.

A long-answer section for 37 marks Two questions: one short, one multi-part Will be graded in detail with part marks awarded

as appropriate only if you show your work. The test will be marked out of 100 points.

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PHY132S Lecture 13 - EM Lecture 5 - Slide 4

PHY132 Mid-Term Test – Don’t Forget ... Your student card. A non-programmable calculator without

text storage and communication capability. A single original, handwritten 22 × 28 cm

sheet of paper on which you have written anything you wish on both sides. Numerical constants will be provided.

One or more dark-black, soft-lead 2B or 2HB pencils and an eraser.

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PHY132S Lecture 13 - EM Lecture 5 - Slide 5

PHY132 Mid-Term Test – Some Advice A good aid-sheet is well organized, easy to

read, and contains all the major equations from the assigned sections from the reading.

Copies of detailed specific problem solutions are unlikely to help.

Be ready to think; get a good night’s sleep tomorrow night.

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PHY132S Lecture 13 - EM Lecture 5 - Slide 6

PHY132 Mid-Term Test – Material Covered 1 All material from Lectures 1 through 13 Waves & Oscillations and Electromagnetism

This includes All assigned sections from the textbook, whether

they were discussed in the lectures or not Lecture notes - sidescreen and tablet All figures and diagrams discussed MasteringPhysics questions Practicals

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PHY132S Lecture 13 - EM Lecture 5 - Slide 7

PHY132 Mid-Term Test – Material Covered 2 The test includes conceptual and

calculation questions

The test does NOT include Supplementary material not discussed in class Integration (BUT you should know the integral

and derivative relationships that we’ve covered)

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PHY132S Lecture 13 - EM Lecture 5 - Slide 8

Physics Drop-In Centre

Location: MP200, right above main lobby Help desk is in small room at North end of Centre

Extended Hours: 10AM - 5PM, Feb. 9-12 and23-26, closed Reading Week

Can just drop in (no need for appointment) Check the schedule at:

http://www.physics.utoronto.ca/undergraduate/dic/dic-schedule.htm

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PHY132S Lecture 13 - EM Lecture 5 - Slide 9

The Waves Section: 8 Classes in 10 Slides The text and our classes often introduced

material in a spiral fashion: the various concepts were introduced in pieces.

Here I try to make the review of that material more linear.

Therefore the review will not always be in the order in which the material was discussed.

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PHY132S Lecture 13 - EM Lecture 5 - Slide 10

Traveling Waves Two views:

• We are at some fixed place and watch thewave go by (history graph)

• We view the wave at a fixed time (snapshotgraph)

For a sinusoidal wave we can combine the twoviews analytically:• Minus sign: wave traveling to the right• Plus sign: wave traveling to the left

Mechanical Waves:• Travel through the medium• Wave speed relative to that medium

)sin(),( 0 tkxAtxD

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PHY132S Lecture 13 - EM Lecture 5 - Slide 11

Traveling Sinusoidal Waves Source: some sort of Simple Harmonic Motion Source stationary relative to the medium:

fwave = fsource

f = v (just d / t = v )• v a property of the medium

Source moving relative to the medium: Doppler Effect: fwave fsource

All Traveling Waves2Amplitude

AreaPowerIntensity

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PHY132S Lecture 13 - EM Lecture 5 - Slide 12

Reflection (incident wave travelingfrom left to right)

Medium to right has as a smaller wave speedthan medium to the left: reflected wave phaseshifted by • This includes a “fixed end”

Medium to right greater speed than medium tothe left: reflected wave not phase shifted• This includes a “free end”

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PHY132S Lecture 13 - EM Lecture 5 - Slide 13

Superposition

Standing Waves: Superposition of incident andreflected waves

Interference: Superposition of two waves withequal wavelengths:• Constructive: two waves in phase• Destructive: two waves out of phase by

Beats: Superposition of two waves with nearlyequal frequencies:• A wave of frequency = the average frequency• Modulated by an amplitude that varies

sinusoidally as ½ the difference in thefrequencies

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PHY132S Lecture 13 - EM Lecture 5 - Slide 14

Superposition – more

The double slit• Maxima: difference in path length m • Minima: difference in path length (m + ½)

Decrease distance d between slits: spread out the interference pattern, and vice versa

“Diffraction” Grating: an array of N slits Reflection Grating: an array of N reflecting

surfaces Diffraction

• Only qualitative• Decrease size of aperture: increase the spread

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PHY132S Lecture 13 - EM Lecture 5 - Slide 15

Superposition – even more!

Interferometers, especially the MichelsonInterferometer

2

2

1

1 )sin()sin(vv

Refraction

Wave Model:

For light:

Total Internal Reflection:

)sin()sin( 2211 nn

)90sin()sin( 021 nn C

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PHY132S Lecture 13 - EM Lecture 5 - Slide 16

Ray Model

Travel in straight lines Can cross (superposition) Travels until it interacts with matter An object is a source of light rays going in all

directions The eye sees by focusing a diverging bundle of

rays

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PHY132S Lecture 13 - EM Lecture 5 - Slide 17

Reflection

incident = reflected

Plane mirror: forms a virtual image

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PHY132S Lecture 13 - EM Lecture 5 - Slide 18

Lenses & Curved MirrorsThins Lens / Thin Mirror Approximation

Parallel rays are brought to a focus at the focal point Distance from lens/mirror to the focal point is the

focal length f

For both ray tracing gives:

Converging lens / Concave mirror: f > 0Diverging lens / Convex mirror: f < 0

s’ > 0: real images’ < 0 : virtual image

Lateral Magnification:

'111ssf

ss

hhm ''

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PHY132S Lecture 13 - EM Lecture 5 - Slide 19

Multiple Thin Lenses / Thin Mirrors

The image of the first is the object for the second

Thick Lens

The image of the first surface is the object forthe second surface

Dispersion For some media, wave speed depends on the

wave frequency Often we talk about the wavelength instead of

the frequency

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PHY132S Lecture 13 - EM Lecture 5 - Slide 20

PHY132 Mid-Term Test – Electromagnetism Review Chapter 26 - all sections

Chapter 27 - §27.1, 27.2, 27.5 in §27.3, we used Equation 27.14 (page 825)

in §27.4, we used Equation 27.26 (page 832)

Chapter 29 - §29.1, 29.2, 29.3

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PHY132S Lecture 13 - EM Lecture 5 - Slide 21

Electric Forces - Coulomb’s Law

q1

q2

rTwo like chargesF2 on 1

F1 on 2

221

o2

211 on 22 on 1 r

qq4

1rqq

KFF

1 on22on1 FF

q1

q2

F2 on 1

F1 on 2Opposite charges

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PHY132S Lecture 13 - EM Lecture 5 - Slide 22

Electric Fields

The electric field describes the electric force on a test charge at any point in space.

q fromaway ,rq

41

'q)z,y,x(F

)z,y,x(E

2o

q' on

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PHY132S Lecture 13 - EM Lecture 5 - Slide 23

Electric Field Lines (for a Dipole)

Tangent to field line is in the direction of the electric field at that point.

Electric dipole moment:

to-from,qs)z,y,x(p

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PHY132S Lecture 13 - EM Lecture 5 - Slide 24

Parallel Plate Capacitor - Uniform Electric Field & Potential Energy

plate to from

,A

QEoo

capacitor

sqE)fi(WU elecelec

qEsUU oelec

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PHY132S Lecture 13 - EM Lecture 5 - Slide 25

Electric Potential Energy of a System of Two Point Charges

rqq

41U 21

oelec

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PHY132S Lecture 13 - EM Lecture 5 - Slide 26

Good Luck!