1Physics 241 – Quiz 1 – Aug. 20, 2019

A point charge q of 1 pC (1×10-12 C) is next to

another charge Q of 1 C at a distance d as

shown. What is the ratio Fq/FQ of the

magnitude of the electric force acting on q to

that of the electric force acting on Q?

a) 1012

b) 106

c) 1

d) 10-6

e) 10-12

q Qd

2Physics 241 – Unscored Question 1

Two point charges are separated by distance d as

shown. Where can you put a third charge of

1 C so that there is no net electric force acting on it?

a) to the right of charge -2Q

b) to the left of charge Q

c) between the two charges

d) some other place

e) nowhere

Q -2Qd

3

Physics 241 – Unscored Question 2

Four point charges are arranged at the corners of a

square as shown. What is the direction of the force

acting on the –Q charge at top left? (Take Q > 0.)

a) toward the lower right

b) toward the upper left

c) upward

d) to the right

e) none of the above- Q

Q

Q

- Q

4

Physics 241 – Quiz 2 (scored) – Aug. 22, 2019

Three point charges are arranged at the corners of a

square as shown. What is the direction of the

electric field at the remaining corner? (Take Q > 0.)

a) toward the lower right

b) toward the upper left

c) upward

d) to the right

e) none of the above- Q

Q

Q

5Physics 241 – Unscored Question 1

The upper half of a rod is uniformly charged with

a positive charge density , whereas the lower half

is uniformly charged with a charge density of −.

What is the direction of the electric field at a point

on the perpendicular bisector and to the right of

the rod as shown?

a) to the right

b) to the left

c) up

d) down

e) E is zeo.

−

6

9/13/2019 6

PHYS241 – Unscored Question 2

y

x

+Q

-Q

A nonconducting semi-circular rod has a uniform charge

Q (>0) distributed uniformly on its top half and -Q

distributed uniformly along its bottom half as shown.

What is the direction of the net electric field at point P?

(A) Towards -x

(B) Towards +x

(C) Towards +y

(D) Towards –y

(E) None of the above

P

7

Physics 241 – Quiz 3 – August 27

The magnitude of the electric field from a single

charged plane of charge density is E = (0).

What is the magnitude of the field at point A?

a) ( ) to the right

b) 3 ( ) to the left

c) to the right

d) to the left

e) 3 ( ) to the right

A

−

8

Physics 241 – Unscored Question 1

The magnitude of the electric field from a single

charged plane of charge density is E = (0).

What is the magnitude of the field at point A?

a) ( ) to the right

b) 3 ( ) to the left

c) to the right

d) to the left

e) 3 ( ) to the right

A

−

9Physics 241 – Unscored Question 2

Two identical point charges are placed at the center

of a large sphere and a small sphere. Which

statement about the net electric flux through the

surface of the spheres is true?

a) The flux is larger for the large sphere.

b) The flux is larger for the small sphere.

c) The flux is the same (and not zero).

d) Not enough information to tell.

e) The flux is zero in both cases.

Q>0 Q>0

10Physics 241 – Unscored Question 3

A point charges Q is at the center of a cube of side

length L and another charge –Q is located directly

below the cube as shown. What is the net outward

electric flux through the surfaces of the cube?

a) Q/L3

b) Q/(06L2)

c) Q/(20)

d) Q/0

e) 0

+Q

-Q

11Physics 241 – Question 4, August 29, 2019

Gauss’s Law states that .

What is the electric field E in this equation?

Choose the best answer.

a) The electric field Eout due only to the charges outside the

enclosed volume must be used.

b) The electric field Ein due only to the charges inside the

enclosed volume must be used.

c) The net electric field Enet due to all the charges both inside

and outside the enclosed volume must be used.

d) Either Ein or Enet can be used since they give the same

integral value anyway.

e) Either Ein or Enet can be used since Ein=Enet anyway.

0/enclosedE ndA Q =

12

A point charge Q is at the center of a cube of edge length L.

What is the flux through one face of the cube?

PHYS241 - Question 4b – Sep. 3, 2019

This replaces the previously given Question 4 if your score

is higher this time. Otherwise the previous one stays.

a) Q /

b) Q /(L2 )

c) Q /

(4 L2)

d) Q /(6 )

e) 0

+Q

13

A charge of Q is placed on the inner conducting

sphere. What is the magnitude of the electric field

inside the conducting shell at radius r shown in blue

below?

Unscored Question 1

a) 0

b) kQ/r2

c) - kQ/r2

d) kQ/r

e) depends on the net

charge on the outer

shell

rQ

14Unscored Question 2

The following picture shows the

electric field lines outside of a

material. Which description best

fits the material?

a) Insulator with uniform positive charge distribution

b) Insulator with uniform negative charge distribution

c) Conductor with negative net charge

d) Conductor with positive net charge

e) Conductor with zero net charge

15

A conducting object has a net charge of 3 C on it. It

also has a hollow region in the interior. If you place a

charge of 2 C in this hollow region, what will be the

total charge on the exterior surface of the object?

2 C

a) 1 C

b) 2 C

c) −2 C

d) −3 C

e) 5 C

PHYS241 - Question 5 – Sep. 3, 2019

16Physics 241 – Unscored Question

Points A and B are located at distance r and 2r,

respectively, from a point charge Q. What is the

potential difference VB−VA?

A BQ

r r

a) -kQ/(2r)

b) kQ/r

c) -2kQ/r

d) kQ/(2r)

e) -(3/2)kQ/(2r)

17

4 charges are located at the corners of a square of

side length d as shown. If q1=q3= q and q2=q4= −q,

what is the electric potential at the center P?

Physics 241 – Question 6 – September 5, 2019

a) 0

b) 5.6kq/d

c) 4kq/d

d) 2.8kq/d

e) 3kq/d

18Physics 241 – Unscored Question 1

The potential due to a particular charge distribution

is measured at several points along x-axis, and the

result is as shown in the figure below. For which of

the following regions of x is Ex < 0 ?

V(x)

x1m 2m 3m

a. 0<x<1 only

b. 1<x<2

c. x>2 only

d. 0<x<1 and x>2

e. at x=1 and x=2

and ,etc.x y

V VE E

x y

= − = −

19Physics 241 – Unscored Question 2

Which of the following describes the equipotential

surfaces due to a thin, uniformly charged plane?

a. Planar surfaces parallel to the charged plane

with decreasing separation closer to it

b. Planar surfaces parallel to the charged plane

with increasing separation closer to it

c. Planar surfaces parallel to the charged plane

with constant separation

20Physics 241 – Unscored Question 3

A conducting sphere of radius 50 cm is charged

with a total charge of Q Coulombs. What is the

potential difference VB-VA in volts?

a) -kQ/2

b) kQ

c) -2kQ

d) kQ/2

e) -(3/2)kQ/2

QA B

1 m

2 m

21Physics 241 – Question 7 – September 10, 2019

Two parallel planes, 2 m apart, are charged with

uniform charge densities 2 and −. Respectively as

shown. What is the potential difference VA-VB?

a) (3/2)/0

b) −2/0

c) − 3/0

d) /0

e) 3/0

A B

2−

2 m

22Physics 241 – Unscored Question 1

We have a parallel plate capacitor made of two

square plates. We could double the capacitance by

a) doubling the separation d

b) doubling charges on the plates Q

c) halving potential difference between the plates V

d) increasing the edge length a of the plates by a factor of 1.4

e) halving the area of the plates A

d

a

Aa

Q

−Q

23Physics 241 – Unscored Question 2

You wish to make a parallel plate capacitor with

C = 8.85 F. If the plates are to be square and

the distance between the plates is to be 0.1 mm,

what would the edge length have to be?

= 8.8510-12 C2/(Nm2)

a) 3.0 10-5 m

b) 100 m

c) 10 m

d) 316 m

e) 3.4 m

24Physics 241 – Question 8 – September 12, 2019

A parallel plate capacitor is charged by a battery.

While the battery remains connected (keeping

potential difference between the plates constant), you

let the plates get closer (with insulated hands). What

happens to the electric field E between the plates?

a) Magnitude of E decreases

b) Magnitude of E increases

c) E remains the same

d) E changes its direction

e) Not enough information to tell