Lecture08 Exam 1 Review

8/3/2019 Lecture08 Exam 1 Review

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adapted from http://www.nearingzero.net (nz118.jpg)

That remindsme… mustpick up test

prep HW.

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http://www.nearingzero.net/



Announcements

Grades spreadsheets will be posted the day after Exam 1. Youwill need your PIN to find your grade. If you haven’t receivedyour PIN yet, it will be on your exam.*

If you lose your PIN, ask (politely and apologetically) your

recitation instructor.

*Hahaha, you can’t look up your exam grade ahead of time! Have to go to recitation.



Know the exam time!

Find your room ahead of time!

If at 5:00 on test day you are lost, go to 104 Physics and check the examroom schedule, then go to the appropriate room and take the exam there.

Exam is from5:00-6:15 pm!

Physics 24 Test Room Assignments, Fall 2011:

Instructor Sections RoomDr. Hagen K, L 295 ToomeyDr. Hale E, G 104 PhysicsDr. Hor J, M 227 FultonDr. Parris B, H 125 Butler-Carlton (Civil)Dr. Peacher D, F G-5 HSSDr. Schmitt A, C 120 Butler-Carlton (Civil)

4:30 and 5:30 Exams 202 PhysicsSpecial Needs Testing Center



Reminders:

No external communication allowed while you are in the

exam room. No texting!Please do not leave the exam room before 5:30 pm.

Be sure to bring a calculator! You will need it.

No headphones.



Do you know the abbreviations for:

milli-

micro-nano-

pico-?

Will you know them by 5:00 pm tomorrow?



Exam 1

Review

The fine print: the problems in this lecture are the standard ―exam reviewlecture problems and are not a guarantee of the exam content.

Please Look at Prior Tests!Caution: spring 2011 exam 1 did not cover capacitors —not true this semester.



Overview

Electric charge and electric force

#Coulomb’s Law Electric field

# * calculating electric field# * motion of a charged particle in an electric field

Gauss’ Law *electric flux# * calculating electric field using Gaussian surfacesproperties of conductors

*Topic of a test preparation homework problem.

#Topic of a review lecture problem.

Exam problems may come from topics not covered ontest preparation homework or during the review lecture.



Overview Electric potential and electric potential energy

# * calculating potentials and potential energy* calculating fields from potentialsequipotentialspotentials and fields near conductors

Capacitorscapacitance of parallel plates, concentric cylinders,(concentric spheres not for this exam)# * equivalent capacitance of capacitor network

# * Don’t forget concepts from physics 23 that we used! *Topic of a test preparation homework problem.

#Topic of a review lecture problem.

Exam problems may come from topics not covered ontest preparation homework or during the review lecture.



F1

F2

+Q

-Q+Q

P

a

x

y

1 2

1 2

ˆ

F F cos F cos iˆ

F sin F sin j

2 2

2 2

2 2

2 2

kQ kQ ˆ

F cos 60 cos 60 ia a

kQ kQ ˆ

sin 60 sin 60 ja a

Three charges +Q, +Q, and – Q, are located at the corners of an equilateral triangle with sides of length a. What is the forceon the charge located at point P (see diagram)?

Note: if there is not a problem like this on Exam 1, there will be one on the Final!



F1

F2

+Q

-Q+Q

P

a

x

y

2

2

kQ ˆ

F 2 cos 60 ia

2

2

kQ ˆ

F ia



F1

F2

+Q

-Q+Q

P

a

x

y

You can repeat the above calculation,replacing F by E.

Or… FEq

2

2

kQ ˆ

2 cos 60 ia

E Q

2

kQ ˆ

E 2 cos 60 ia

What is the electric field at P due to the two charges at thebase of the triangle?



A ring with radius R has a uniform charge density . Calculatethe potential difference between the point at the center of thering and a point on the axis of the ring that is a distance of 3R from the center of the ring.

R

3R



enclosed

o o

q 2QE dA

An insulating spherical shell has an inner radius b and outer radius c. Theshell has a total charge Q and a uniform charge density. Concentric with theshell is a solid conducting sphere of total charge 2Q and radius a<b. Find

the magnitude of the electric field for a<r<b .

Be able to do this: begin with a statement of Gauss’s Law. Draw anappropriate Gaussian surface on the diagram and label its radius r . Justifythe steps leading to your answer.

This looks like a test preparation homework problem, but it is different!



enclosed

o

qE dA

3 3

2

o

4 4r a 2Q

3 3E 4 r

3 3shell

4 4Q b a

3 3

An insulating spherical shell has an inner radius b and outer radius c. Theshell has a total charge Q and a uniform charge density. Concentric with theshell is a solid conducting sphere of total charge 2Q and radius a<b. Find

the magnitude of the electric field for b<r<c .

What would be different if we had concentric cylinders instead of concentric spheres?What would be different if the outer shell were a conductor instead of an insulator?



f iV V V Ed

f i other i f E E E W .

U q V

An electron has a speed v. Calculate the magnitude anddirection of an electric field that will stop this electron in adistance D.

Do you understandthat these E’s havedifferent meanings?

Use magnitudes if youhave determined directionof E by other means.

Know where thiscomes from!



Possible variation on the previous problem (the ―same problem, but students would disagree)…

…calculate the closest the electron would come to anotherelectron.

You can also use kinematics to solve this problem.



QQ

P

a

Two equal positive charges Q are located at the base of anequilateral triangle with sides of length a. What is the potentialat point P (see diagram)?



QQ

P

a

An electron initially at rest an infinite distance away movesunder the influence of the electric field until it reaches point P.What is the speed of the electron at point P?



QQ

P

a

Q

Three equal positive charges Q are located at the corners of anequilateral triangle with sides of length a. What is the potentialenergy of the charge located at point P (see diagram)?

What would happen if the charges were held at rest in the above configuration, and

then released?



If you need to evaluate an integral on tomorrow’s exam, youwill be given the integral.

If you don’t know what you are doing, pretend that you do andwrite stuff down. You might know more than you think you do!



For the capacitor system shown, C 1=6.0 F, C2=2.0 F, andC3=10.0 F. (a) Find the equivalent capacitance.

V 0

C 1

C 2 C 3



For the capacitor system shown, C 1=6.0 F, C2=2.0 F, andC3=10.0 F. (b) The charge on capacitor C 3 is found to be 30.0

C. Find V 0.

V 0

C 1

C 2 C 3



Lecture 1:

Coulomb’s Law (electrical force between charged particles). You must be able to calculate the electrical forces between two or more charged particles.

Lecture 2:

The electric field. You must be able to calculate the force on a charged particle in an electric field.

Electric field of due to a point charge. You must be able to calculate electric field of a point charge.

Motion of a charged particle in a uniform electric field. You must be able to solve for the trajectory of a charged particle in a uniform electric field.

The electric field due to a collection of point charges. You must be able to calculate electric field of a collection of point charges.

The electric field due to a continuous line of charge. You must be able to calculate electric field of a continuous line of charge.

Summary of all the ―things you must be able to do slides.



Lecture 3:

The electric field of a dipole. You must be able to calculate the electric field of a dipole.

The electric field due to a collection of point charges (continued). You must be able to calculate the electric field of a collection of point charges.

Electric field lines. You must be able to draw electric field lines, and interpret diagrams that show electric field lines.

A dipole in an external electric field. You must be able to calculate the moment of an electric dipole, the torque on a dipole in an externalelectric field, and the energy of a dipole in an external electric field.

Lecture 4:

Electric flux. You must be able to calculate the electric flux through a surface.

Gauss’ Law. You must be able to use Gauss’ Law to calculate the electric field of a high -symmetry chargedistribution.

Conductors in electrostatic equilibrium. You must be able to use Gauss’ law to draw conclusions about the behavior of charged particles on, andelectric fields in, conductors in electrostatic equilibrium.



Lecture 5:

Electric potential energy. You must be able to use electric potential energy in work-energy calculations.

Electric potential. You must be able to calculate the electric potential for a point charge, and use the electric potential inwork-energy calculations.

Electric potential and electric potential energy of a system of charges. You must be able to calculate both electric potential and electric potential energy for a system of charged particles (point charges today, charge distributions next lecture).

The electron volt. You must be able to use the electron volt as an alternative unit of energy.



Lecture 6:

Electric potential of a charge distribution. You must be able to calculate the electric potential for a charge distribution.

Equipotentials. You must be able to sketch and interpret equipotential plots.

Potential gradient. You must be able to calculate the electric field if you are given the electric potential.

Potentials and fields near conductors. You must be able to use what you have learned about electric fields, Gauss’ law, and electric potentialto understand and apply several useful facts about conductors in electrostatic equilibrium.

Lecture 7:

Capacitance. You must be able to apply the equation C=Q/V.

Capacitors: parallel plate, cylindrical, spherical. You must be able to calculate the capacitance of capacitors having these geometries, and you must beable to use the equation C=Q/V to calculate parameters of capacitors.

Circuits containing capacitors in series and parallel. You must be understand the differences between, and be able to calculate the ―equivalent capacitance of, capacitors connected in series and parallel.

Lecture08 Exam 1 Review

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