1. ConcepTest 16.1a1. ConcepTest 16.1a Electric Charge IElectric Charge I

1) one is positive, the other

is negative

2) both are positive

3) both are negative

4) both are positive or both

are negative

Two charged balls are Two charged balls are

repelling each other as repelling each other as

they hang from the ceiling. they hang from the ceiling.

What can you say about What can you say about

their charges?their charges?

1) have opposite charges

2) have the same charge

3) all have the same charge

4) one ball must be neutral (no charge)

From the picture, From the picture,

what can you what can you

conclude about conclude about

the charges?the charges?

2. ConcepTest 16.1b2. ConcepTest 16.1b Electric Charge IIElectric Charge II

3. ConcepTest 16.2a3. ConcepTest 16.2a Conductors IConductors I

1) positive

2) negative

3) neutral

4) positive or neutral

5) negative or neutral

A metal ball hangs from the ceiling

by an insulating thread. The ball is

attracted to a positive-charged rod

held near the ball. The charge of

the ball must be:

Two neutral conductors are connected

by a wire and a charged rod is brought

near, but does not touch. The wire is

taken away, and then the charged rod

is removed. What are the charges on

the conductors?

4. ConcepTest 16.2b4. ConcepTest 16.2b Conductors IIConductors II1) 0 0

2) + –

3) – +

4) + +

5) – –

0 0

? ?

QQ QQF1 = 3N F2 = ?

1) 1.0 N

2) 1.5 N

3) 2.0 N

4) 3.0 N

5) 6.0 N

What is the magnitude What is the magnitude

of the force Fof the force F22??

5. ConcepTest 16.3a5. ConcepTest 16.3a Coulomb’s Law ICoulomb’s Law I

6. ConcepTest 16.3b6. ConcepTest 16.3b Coulomb’s Law IICoulomb’s Law II

1) 3/4 N

2) 3.0 N

3) 12 N

4) 16 N

5) 48 N

If we increase one charge to If we increase one charge to 4Q4Q, ,

what is the magnitude ofwhat is the magnitude of F F11??

4Q4Q QQF1 = ? F2 = ?

QQ QQF1 = 3N F2 = ?

1) 9 F

2) 3 F

3) F

4) 1/3 F

5) 1/9 F

The force between two charges

separated by a distance d is F. If

the charges are pulled apart to a

distance 3d, what is the force on

each charge?

QQFF

QFF

dd

QQ??

QQ??

33dd

7. ConcepTest 16.3c7. ConcepTest 16.3c Coulomb’s Law IIICoulomb’s Law III

8. ConcepTest 16.4a8. ConcepTest 16.4a Electric Force IElectric Force I

1) yes, but only if QQ00 is positiveis positive

2) yes, but only if QQ00 is negativeis negative

3) yes, independent of the sign (or

value) of QQ00

4) no, the net force can never be

zero

Two balls with charges Two balls with charges ++QQ and and +4+4QQ

are fixed at a separation distance are fixed at a separation distance

of of 33RR. Is it possible to place . Is it possible to place

another charged ball another charged ball QQ00 on the line on the line

between the two charges such that between the two charges such that

the net force on the net force on QQ00 will be zero? will be zero?

3R

+Q +4Q

Two balls with charges Two balls with charges ++QQ and and +4+4QQ are separated by are separated by 33RR. Where . Where

should you place another charged ball should you place another charged ball QQ00 on the line between on the line between

the two charges such that the net force on the two charges such that the net force on QQ00 will be zero? will be zero?

3R

+Q +4Q

R 2R

1 2 3 4 5

9. ConcepTest 16.4b9. ConcepTest 16.4b Electric Force IIElectric Force II

3R

+Q –– 4Q

Two balls with charges Two balls with charges ++QQ and and ––44QQ

are fixed at a separation distance are fixed at a separation distance

of of 33RR. Is it possible to place . Is it possible to place

another charged ball another charged ball QQ00 anywhereanywhere

on the line such that the net force on the line such that the net force

on on QQ00 will be zero? will be zero?

10. ConcepTest 16.4c10. ConcepTest 16.4c Electric Force IIIElectric Force III

1) yes, but only if QQ00 is positiveis positive

2) yes, but only if QQ00 is negativeis negative

3) yes, independent of the sign (or

value) of QQ00

4) no, the net force can never be

zero

A proton and an electron are

held apart a distance of 1 m

and then released. As they

approach each other, what

happens to the force between

them?

1) it gets bigger

2) it gets smaller

3) it stays the same

p e

11. ConcepTest 16.5a11. ConcepTest 16.5a Proton and Electron IProton and Electron I

1) proton

2) electron

3) both the same

p e

12. ConcepTest 16.5b12. ConcepTest 16.5b Proton and Electron IIProton and Electron II

A proton and an electron are held

apart a distance of 1 m and then

released. Which particle has the

larger acceleration at any one

moment?

A proton and an electron

are held apart a distance

of 1 m and then let go.

Where would they meet?

1) in the middle

2) closer to the electron’s side

3) closer to the proton’s side

p e

13. ConcepTest 16.5c13. ConcepTest 16.5c Proton and Electron IIIProton and Electron III

Which of the arrows best

represents the direction

of the net force on charge

+Q due to the other two

charges?

+2Q

+4Q

+Q

1 23

4

5d

d

14. ConcepTest 16.614. ConcepTest 16.6 Forces in 2DForces in 2D

(1) 44 EE00

(2) 22 EE00

(3) EE00

(4) 1/21/2 EE00

(5) 1/44 EE00

You are sitting a certain distance from You are sitting a certain distance from

a point charge, and you measure an a point charge, and you measure an

electric field of electric field of EE00. If the charge is . If the charge is

doubleddoubled and your distance from the and your distance from the

charge is also charge is also doubleddoubled, what is the , what is the

electric field strength now?electric field strength now?

15. ConcepTest 16.715. ConcepTest 16.7 Electric FieldElectric Field

+2 +1+1 +1d d

1)

2)

3) the same for both

Between the red and the

blue charge, which of

them experiences the

greater electric field due

to the green charge?

16. ConcepTest 16.8a16. ConcepTest 16.8a Field and Force IField and Force I

+2

+1

+2 +1+1 +1d d

1)

2)

3) the same for both

Between the red and the

blue charge, which of

them experiences the

greater electric force due

to the green charge?

17. ConcepTest 16.8b17. ConcepTest 16.8b Field and Force IIField and Force II

+2

+1

What is the electric field at What is the electric field at

the center of the square?the center of the square?

43

2 1

-2 C

-2 C

5) E = 0

18. ConcepTest 16.9a18. ConcepTest 16.9a Superposition ISuperposition I

43

2 1

-2 C

-2 C -2 C

-2 C

19. ConcepTest 16.9b19. ConcepTest 16.9b Superposition IISuperposition II

What is the electric field at What is the electric field at

the center of the square?the center of the square?

5) E = 0

What is the direction of

the electric field at the

position of the X ?

4

32

1

+Q

-Q +Q

5

20. ConcepTest 16.9c20. ConcepTest 16.9c Superposition IIISuperposition III

1) charges are equal and positive

2) charges are equal and negative

3) charges are equal and opposite

4) charges are equal, but sign is

undetermined

5) charges cannot be equal

Q2Q1 x

y

E

Two charges are fixed along Two charges are fixed along

the the xx-axis. They produce an -axis. They produce an

electric field electric field EE directed along directed along

the negative the negative yy-axis at the -axis at the

indicated point. Which of indicated point. Which of

the following is true?the following is true?

21. ConcepTest 16.1021. ConcepTest 16.10 Find the ChargesFind the Charges

Q

In a uniform electric field in empty In a uniform electric field in empty

space, a 4 C charge is placed and it space, a 4 C charge is placed and it

feels an electrical force of 12 N. If feels an electrical force of 12 N. If

this charge is removed and a 6 C this charge is removed and a 6 C

charge is placed at that point charge is placed at that point

instead, what force will it feel?instead, what force will it feel?

1) 12 N

2) 8 N

3) 24 N

4) no force

5) 18 N

22. ConcepTest 16.1122. ConcepTest 16.11 Uniform Electric FieldUniform Electric Field

23. ConcepTest 16.12a 23. ConcepTest 16.12a Electric Field Lines IElectric Field Lines I

What are the signs of the

charges whose electric

fields are shown at right?

1)

2)

3)

4)

5) no way to tell

24. ConcepTest 16.12b24. ConcepTest 16.12b Electric Field Lines IIElectric Field Lines II

Which of the charges has

the greater magnitude?

1)

2)

3) Both the same