FY1003 Electricity and Magnetism 2020

Formell melding til studenter om endring av vurderingsform

Som en konsekvens av Covid-19 utbruddet så arrangeres det ingen eksamener med fysisk oppmøte på campus i år. Det medfører at eksamen må gjennomføres digitalt i FY1003 Elektrisitet og Magnetisme og vurderingsform er endret fra skriftlig eksamen til hjemmeeksamen.

Merk at eksamensdato og tidspunkt for eksamen er det samme som opprinnelig oppsatt.

De av dere som har vedtak på ekstra tid på eksamen vil fortsatt ha dette selv om eksamensformen er endret. Endringer i eksamensformen vil etterhvert dukke opp på studentweb også. Dette må endres manuelt så det kan ta litt tid før alle endringer er på plass. Karakterregelen for dette emnet er også endret fra bokstavkararene A-F til bestått/ikke bestått.

Info

Lectures: All lectures in this course are cancelled due to the Covid-19 virus. Therefore, all students have to study on their own according to the lecture plan given below on this page. To facilitate this, the following has been implemented

I have made my own lecture notes for chapter 28 and 29 available in the section "Useful links". I will make lecture notes for the remaining chapters available soon (probably Monday next week).
There are also video lectures available for this course from a previous year (the curriculum was very similar) - see the page "Teaching".
I have made Mentimeter multiple choice questions available so that you can test your own knowledge at various points - more info in the section "Useful links".
I have created a discussion forum on Blackboard where students may post and discuss answer questions and comments regarding topics in the course with each other. I will also log in on a regular basis to give input.
There will be three question hours arranged on the following dates: May 14th, May 21st, May 28th. The question hour is arranged as follows: students may send me emails (jacob.linder@ntnu.no) with questions about the exam or questions about topics in the curriculum, problemsolving et.c., and then I will post a video on each of the abovementioned dates where I go through these questions and answer them. The videos will appear at the bottom of this page.

Regarding laboratory exercises and written/numerical exercises, the consequences are as follows:

Exercises: The exercises now have to be done at home and handed in to the teaching assistant via mail for approval. The deadline for handing in the exercises is on Thursdays at 23:59. If you want your exercise to be graded, you can ask for this.

Laboratories: All remaining laboratory exercises are cancelled until further notice. Cancelled labs will be automatically approved for all students.

Exam

The exam will, as mentioned above, be a home-exam on the same day as originally planned and of the same duration (4 hours). The grading will be passed or not passed. Passed will be given to those with a score of more than 40%. All examination aids are allowed, but you are not allowed to collaborate with others. The exam will consist of a mixture of multiple choice questions and regular problems. The multiple choice questions will in some cases require analytical calculations and extracting numerical answers. No scanning/photography will be required - you will be able to write all answers to the exam questions in Inspera.

Previous exams in this course will give an indicator of what type of questions you can expect both on the multiple choice part and for the regular problems. Out of all previous exams, this year's exam will resemble the 2019 exam the most in terms of structure. The type of questions/problems given on the 2019 exam are also representative of the type of questions/problem you can expect on this year's exam. Therefore, if you want to have a "prøveeksamen", the 2019 exam serves this purpose well.

This year's exam will be of similar difficulty and similar extent as in previous years.

Questions about exam: If you have any questions regarding the exam, please send them to Jacob Linder and I will post the answer to the most common questions here.

Timetable

Lectures

Mondays 10:15-12:00 in H3
Tuesdays 12:15-14:00 in S5

Exercises/lab/numerical project

All information about exercises is found on Blackboard.

Reference group

• Veslemøy Osmundsen (vtosmund@stud.ntnu.no, MTFYMA)

• Maya Retzius (mayamr@stud.ntnu.no, MTFYMA)

• Mahtab Zamanian Fardshahri (mahtabz@stud.ntnu.no, MTFYMA)

• Edvard Jortveit (edvard98@gmail.com, MTFYMA)

• Mattias Gjerdset Nyttingnes (mattiagn@stud.ntnu.no, BFY)

• Saule Trepekunaite (saulett@stud.ntnu.no, MLREAL)

Summary of the first reference group meeting (January) and the second reference group meeting (March).

Exam

The exam date is June 2nd, 2020.

The exam will be digital - read more about digital exams on NTNUs webpages.

The exam will be a home-exam on the same day as originally planned and of the same duration (4 hours). The grading will be passed or not passed. Passed will be given to those with a score of more than 40%.

All examination aids are allowed, but you are not allowed to collaborate with others.

Question hour

To be announced. If you send your questions in advance via email, I will be able to provide a more thorough answer.

Curriculum

The topics covered in the lectures defines the curriculum and is almost entirely covered by the following chapters in Young & Freedman, University Physics (13th edition). Other editions, such as the 12th and 14th, can also be used.

Electrostatics

• Electric charge and field: 21.1 - 21.7

• Gauss law: 22.1 - 22.5

• Electric potential 23.1 - 23.5

• Capacitance and dielectrics: 24.1 - 24.6

• Current, resistance, EMS: 25.1 - 25.6

• DC circuits: 26.1, 26.2, 26.3, 26.4

Magnetostatics

• Magnetic field and magnetic forces: 27.1 - 27.9

• Sources of magnetic fields: 28.1 - 28.8

Electrodynamics

• Electromagnetic induction: 29.1 - 29.5, 29.7

• Inductance: 30.1 - 30.4

• AC circuits: 31.1 - 31.3, 31.5

• Electromagnetic waves: 32.1 - 32.4

Other useful information

The following textbook has Norwegian text and also covers a great deal of the topics listed above: Lillestøl, Hunderi og Lien, Generell fysikk for universiteter og høyskoler, bind 2, Varmelære og elektromagnetisme. Universitetsforlaget 2001 (Kap. 19-28).

List of the connection between topic and chapter number in Y&F as well as Lillestøl, Hunderi og Lien.

Here is a non-exclusive checklist for topics which are important to master prior to the exam.

For a discussion regarding mutual inductance and why M_12 = M_21, click here. A mathematical proof using the vector potential (B = curl A) is given here.

Lecture plan

Rough plan for the semester - deviations may occur.

Week 2 (January)
Chapter 21

Week 3
Cont. chapter 21 + chapter 22

Week 4
Cont. chapter 22 + chapter 23

Week 5
Cont. chapter 23 + chapter 24

Week 6 (February)
Cont. chapter 24 + chapter 25

Week 7
Cont. chapter 25 + chapter 26

Week 8
Cont. chapter 26

Week 9
Cont. chapter 26 + Chapter 27

Week 10 (March)
Cont. Chapter 27

Week 11
Cont. chapter 27

Week 12
Chapter 28

Week 13
Cont. chapter 28 + chapter 29

Week 14 (April)
Chapter 29 + chapter 30

Week 15
Easter holiday

Week 16
Cont. chapter 30 + chapter 31

Week 17
Chapter 32

Week 18
Summary

Useful links

Lecture notes

Lecture notes for chapter 28 and 29.

Lecture notes for chapter 30, 31, and 32.

Survival course for mathematics in electricity and magnetism.

If you want to prepare for the lectures in this course, you can either read in Freedman & Young or look at the following slides for the lectures which were prepared in 2011 (the curriculum is very similar to the present year).

• Chapter 21

• Chapter 22

• Chapter 23

• Chapter 24

• Chapter 25

• Chapter 26

• Chapter 27

• Chapter 28

• Chapter 29

• Chapter 30

• Chapter 31

• Chapter 32

Mentimeter test questions

Test your knowledge on various questions below. Click to expand the text and get the correct answer with explanation.

Exams from previous years

These are available here, except the 2019 exam:

2019 problem text and 2019 solution (slightly more detailed solution for problems 21-26 in Norwegian text given here). The formula sheet for 2019 is here.

Miscellaneous

ENT3R Trondheim (Realfagsrekruttering for studenter)
https://www.ent3r.no/jeg-vil-bli-mentor/sok-her/?form=18
https://www.youtube.com/watch?v=DaxtE-5wQ14

Mentimeter questions

Mentimeter answers

Answer 28.1

Correct answer is d): the B-field produced is determined by v x r, so when v || r, B = 0.

Answer 28.2

Correct answer is f): the B-field at any point along a line in front or behind of a straight current-carrying wire is zero, since v || r. Therefore, only the middle segment of the wire contributes.

Answer 28.3

Correct answer is (b) : the field is zero outside and B is perpendicular to the integral path for all segments except ab.

Answer 28.4

Correct answer is (b): using Ampere's law, we find that the field increases linearly with radius up to r=R and then starts to decrease. The maximum field is thus obtained at r=R.

Answer 29.1

Correct answer is (a): according to Lenz law, an EMF is established so that the induced current creates a magnetic field that opposes the change in magnetic flux that initially caused it.

Answer 29.2

Correct answer is (a): to begin with, the rod PQ is balanced by downward acting graviational force and upward acting magnetic force from the B-field. When theta is reduced below theta_1, two things happen: 1) the gravitational force diminishes and the rod starts moving upwards and 2) the magnetic flux through the closed loop increases since the area of the loop becomes more perpendicular to the B-field, which in turn induces an EMF and current in the same direction as the existing current. This causes the rod to accelerate upwards. However, as it moves upward, the magnetic flux will now start to decrease since the area of the loop is reduced. This induces an EMF and current in the opposite direction of the current driven by the battery. In the end, a stationary situation is reached where the current moves upward with a constant velocity. To formally see this, I strongly recommend that you try to set up Newton's law ma = force_upward - force_downward and solve this equation for the velocity.

Answer 29.3

Correct answer is (c): when the capacitor is charging, the electric field between the plate increases. In this situation, a displacement current exists (time-dependent electric flux) which in turn induces a magnetic field.

Answer 29.4

Correct answer is (c): Don't fall for the temptation to conclude from the equation div D = rho_free that the displacement field is zero just because there is no free charge (rho_free = 0). No free charge means that the divergence of D is zero, not that D is zero. Therefore, (c) is the correct answer.

Answer 30.1

Correct answer is (b): when the switch is in position a, the capacitor becomes fully charged when it has a charge Q = CV. When the switch changes to position b, the initial condition is thus that Q=CV and that there is no current flowing. Now, we can use Kirchhoff's law for voltage to set up a differential equation for charge. Namely, the sum of the voltage drops over C and L must equal zero. Thus, we get Q/C + L*dI/dt=0 where I=dQ/dt. In effect, we have a 2nd order diff eq for Q:

d^2Q/dt^2 + Q/LC = 0

General solution is Q = A*cos(k*t) + B*sin(k*t) where k = 1/sqrt(LC). Using the abovementioned initial conditions for Q and I=dQ/dt, we find that B = 0 and A = CV. Thus, the charge on C is:

Q(t) = CV*cos(t/sqrt(LC))

where t is time. Since I=dQ(t)/dt, we see that the current amplitude scales as 1/sqrt(L). Therefore, if one changes L -> L/2, the current amplitude increases by a factor sqrt(2).

As for the period, we see from the solution of Q(t) that it is given as T = 2*pi*sqrt(LC). Therefore, changing L -> L/2 reduces the period by a factor sqrt(2).

Answer 30.2

Correct answer is (b) if by maximum of the current one means the maximum amplitude: when the switch changes to position b, the current is zero and will after that start oscillating (as explained in the answer to 30.1) as a sin-function. Therefore, the first maximum of the amplitude will occur after a quarter period. If one instead means the maximum of the actual -sin form of the current, the maximum occurs after three quarters of a period.

Questions hours

#1, May 14th

Covering questions from students + talking about displacement current as a concept and it's relation to Ampere's law.

#2, May 21st

Covering the following topics: non-conservative electric fields induced by time-varying magnetic fields as well as phasors and reactance in AC circuits.

#3, May 28th

Covering questions from students + giving a brief intro to impedance and EM waves.

PS: In the problem with the potential difference between two concentric shells, there is a minus sign missing on the right-hand side of the equation in line 1 and 2 of the answer that I have written.

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