unit 17 conceptual review

7/18/2019 Unit 17 Conceptual Review

http://slidepdf.com/reader/full/unit-17-conceptual-review 1/35

© 2005 Pearson Prentice Hall

This work is protected by United States copyright laws and is provided solely for

the use of instructors in teaching their courses and assessing student learning!isse"ination or sale of any part of this work #including on the $orld $ide $eb%

will destroy the integrity of the work and is not per"itted The work and "aterials

fro" it should never be "ade available to students e&cept by instructors using

the acco"panying te&t in their classes 'll recipients of this work are e&pected to

abide by these restrictions and to honor the intended pedagogical purposes and

the needs of other instructors who rely on these "aterials

ConcepTest PowerPoints

(hapter )*

Physics: Principles with

Applications, 6 th edition

+iancoli



ConcepTest 17.1aConcepTest 17.1a ,lectric Potential ,nergy -,lectric Potential ,nergy -

)% proton

2% electron

.% both feel the sa"e force

/% neither there is no force

5% they feel the sa"e "agnitudeforce but opposite direction

E

electronelectron

protonproton

E

electronelectron

protonproton11

'' protonproton and anand an electronelectron are inare in

a constant electric field createda constant electric field created

by oppositely charged platesby oppositely charged plates 3ou release the 3ou release the protonproton fro" thefro" the

positivepositive side and theside and the electronelectron

fro" thefro" the negativenegative side $hichside $hich

feels the larger electric force4feels the larger electric force4



ConcepTest 17.1aConcepTest 17.1a ,lectric Potential ,nergy -,lectric Potential ,nergy -

)% proton

2% electron

.% both feel the sa"e force

/% neither there is no force

5% they feel the sa"e "agnitudeforce but opposite direction

E

electronelectron

protonproton

E

electronelectron

protonproton11

Since F = qE F = qE and the proton and electron

have the sa"e charge in "agnitudesa"e charge in "agnitude they

both e&perience the sa"e forcesa"e force However

the forces point in opposite directionsopposite directions

because the proton and electron are

oppositely chargedoppositely charged






feels the larger electric force4feels the larger electric force4



E

electronelectron

protonproton

E

electronelectron

protonproton11

)% proton

2% electron

.% both feel the sa"e acceleration

/% neither there is no acceleration

5% they feel the sa"e "agnitudeacceleration but opposite direction






has the larger acceleration4has the larger acceleration4

ConcepTest 17.1bConcepTest 17.1b ,lectric Potential ,nergy --,lectric Potential ,nergy --



E

electronelectron

protonproton

E

electronelectron

protonproton11

)% proton

2% electron

.% both feel the sa"e acceleration

/% neither there is no acceleration

5% they feel the sa"e "agnitudeacceleration but opposite direction

Since F = aF = a and the electron is "uch lesselectron is "uch less

"assive"assive than the proton then the electronelectron

e&periences the larger acceleratione&periences the larger acceleration






has the larger acceleration4has the larger acceleration4

ConcepTest 17.1bConcepTest 17.1b ,lectric Potential ,nergy --,lectric Potential ,nergy --



E

electronelectron

protonproton

E

electronelectron

protonproton11

)% proton

2% electron

.% both ac6uire the sa"e 7,

/% neither there is no change of7,

5% they both ac6uire the sa"e 7,

but with opposite signs

ConcepTest 17.1c ConcepTest 17.1c ,lectric Potential ,nergy ---,lectric Potential ,nergy ---





fro" thefro" the negativenegative side $henside $hen

it strikes the opposite plateit strikes the opposite plate

which one has "ore 7,4which one has "ore 7,4



E

electronelectron

protonproton

E

electronelectron

protonproton11

)% proton

2% electron

.% both ac6uire the sa"e 7,

/% neither there is no change of7,

5% they both ac6uire the sa"e 7,

but with opposite signs

Since P, 8P, 8 q! q! and the proton and electron

have the sa"e charge in "agnitudesa"e charge in "agnitude they

both have the sa"e electric potential energysa"e electric potential energy

initially 9ecause energy is conserved they

both "ust have the sa"e kinetic energysa"e kinetic energy after

they reach the opposite plate

ConcepTest 17.1c ConcepTest 17.1c ,lectric Potential ,nergy ---,lectric Potential ,nergy ---





fro" thefro" the negativenegative side $henside $hen

it strikes the opposite plateit strikes the opposite plate

which one has "ore 7,4which one has "ore 7,4



$hich group of charges took ore wor" to bring together

fro" a very large initial distance apart4

1)

1)

1)

d d

d

1)12d

9oth took the sa"e a"ount of work

ConcepTest 17.# ConcepTest 17.# $ork and Potential ,nergy$ork and Potential ,nergy



The work needed to asse"ble

a collection of charges is thesa"e as the total P,total P, of those

charges:

r

$ $ " PE

21

$hich group of charges took ore wor" to bring together

fro" a very large initial distance apart4

1)

1)

1)

d d

d

1)12d

9oth took the sa"e a"ount of work

;or case ):;or case ): onlyonly )) pair pair

d " d " PE

212

%%##

;or case 2:;or case 2: there arethere are .. pairspairs

d " d " PE

1

3

11

3

%%##added overadded over

all pairsall pairs

ConcepTest 17.# ConcepTest 17.# $ork and Potential ,nergy$ork and Potential ,nergy



)% ! < 0

2% ! 8 0

.% ! = 0

AA BB

$hat is the electric$hat is the electric

potential at point '4potential at point '4

ConcepTest 17.%aConcepTest 17.%a ,lectric Potential -,lectric Potential -



Since $ # #which is positivepositive% is closer closer

to point ' than $ 1 #which is negative%

and since the total potential is e6ual

to ! 1 & ! # then the total potential is

positivepositive

)% ! < 0

2% ! 8 0

.% ! = 0

AA BB


potential at point '4potential at point '4

ConcepTest 17.%aConcepTest 17.%a ,lectric Potential -,lectric Potential -



)% ! < 0

2% ! 8 0

.% ! = 0

AA BB


potential at point 94potential at point 94

ConcepTest 17.%bConcepTest 17.%b ,lectric Potential --,lectric Potential --



Since $ # and $ 1 are e6uidistant

fro" point 9 and since they have

e6ual and opposite charges then

the total potential is >ero>ero

)% ! < 0

2% ! 8 0

.% ! = 0

AA BB


potential at point 94potential at point 94

ConcepTest 17.%bConcepTest 17.%b ,lectric Potential --,lectric Potential --

;ollowup:;ollowup: $hat is the potential$hat is the potential

at the origin of theat the origin of the '(y '(y a&es4a&es4



;our point charges are;our point charges are

arranged at the corners of aarranged at the corners of a

s6uare ;ind thes6uare ;ind the electricelectric

fieldfield E E and theand the potentialpotential ! ! atat

thethe center of the s6uarecenter of the s6uare

)% E 8 0 ! 8 0

2% E 8 0 ! ≠

0

.% E ≠ 0 ! ≠ 0

/% E ≠ 0 ! 8 0

5% E 8 ! regardless of the value

$ $

$ $ 11$ $

11$ $

ConcepTest 17.)ConcepTest 17.) Hollywood S6uareHollywood S6uare



;our point charges are;our point charges are

arranged at the corners of aarranged at the corners of a

s6uare ;ind thes6uare ;ind the electricelectric

fieldfield E E and theand the potentialpotential ! ! atat

thethe center of the s6uarecenter of the s6uare

)% E 8 0 ! 8 0

2% E 8 0 ! ≠

0

.% E ≠ 0 ! ≠ 0

/% E ≠ 0 ! 8 0

5% E 8 ! regardless of the value

$ $

$ $ 11$ $

11$ $

The potential is >eropotential is >ero: the scalar

contributions fro" the two positive

charges cancel the two "inus charges

However the contributions fro" the

electric field add up as vectors and

they do not cancel #so it is non>eroit is non>ero%

ConcepTest 17.)ConcepTest 17.) Hollywood S6uareHollywood S6uare

;ollowup:;ollowup: $hat is the direction$hat is the direction

of the electric field at the center4of the electric field at the center4



't which point't which point

doesdoes ! ! 8 048 04

)

.

2

/

1$ $

5% all of the"

ConcepTest 17.*aConcepTest 17.*a ,6uipotential Surfaces -,6uipotential Surfaces -



't which point't which point

doesdoes ! ! 8 048 04

)

.

2

/

1$ $

5% all of the"

'll of the points are e6uidistant fro" both charges'll of the points are e6uidistant fro" both charges Since

the charges are e6ual and opposite their contributions to

the potential cancel outcancel out everywhereeverywhere along the "idplane

between the charges

ConcepTest 17.*aConcepTest 17.*a ,6uipotential Surfaces -,6uipotential Surfaces -

;ollowup:;ollowup: $hat is the direction of the electric field at all /$hat is the direction of the electric field at all /



$hich of these configurations gives ! 8 0 at all points on the ' a&is4

/% all of the above 5% none of the above

)%

&

12 (

2

(

1) (

)

(

2%

&

12 (

)

(

1) (

2 (

.%

&

12 (

)

(

2 (

1) (

ConcepTest 17.*bConcepTest 17.*b ,6uipotential Surfaces --,6uipotential Surfaces --



?nly in case #)% where opposite charges lie

directly across the ' a&is fro" each other dothe potentials fro" the two charges above the

' a&is cancel the ones below the ' a&is

$hich of these configurations gives ! 8 0 at all points on the ' a&is4


)%

&

12 (

2

(

1) (

)

(

2%

&

12 (

)

(

1) (

2 (

.%

&

12 (

)

(

2 (

1) (

ConcepTest 17.*bConcepTest 17.*b ,6uipotential Surfaces --,6uipotential Surfaces --



$hich of these configurations gives ! 8 0 at all points on the y a&is4


ConcepTest 17.*c ConcepTest 17.*c ,6uipotential Surfaces ---,6uipotential Surfaces ---

)%

&

12 (

2

(

1) (

)

(

2%

&

12 (

)

(

1) (

2 (

.%

&

12 (

)

(

2 (

1) (



$hich of these configurations gives ! 8 0 at all points on the y a&is4


ConcepTest 17.*c ConcepTest 17.*c ,6uipotential Surfaces ---,6uipotential Surfaces ---

)%

&

12 (

2

(

1) (

)

(

2%

&

12 (

)

(

1) (

2 (

.%

&

12 (

)

(

2 (

1) (

?nly in case #.% where opposite charges lie

directly across the y a&is fro" each other dothe potentials fro" the two charges above the

y a&is cancel the ones below the y a&is

;ollowup:;ollowup: $here is$here is ! ! 8 0 for configuration @248 0 for configuration @24



$hich two points have$hich two points have

thethe sa"esa"e potential4potential4

)% ' and (

2% 9 and ,

.% 9 and !

/% ( and ,

5% no pair

'

(

9 !,$

ConcepTest 17.6 ConcepTest 17.6 ,6uipotential of Point (harge,6uipotential of Point (harge



Since the potential of a point charge is:

only points that are at the sa"e distancesa"e distance fro" charge A are at the sa"e potentialsa"e potential

This is true for points ( and ,

They lie on an Eq+ipotential +r-aceEq+ipotential +r-ace

$hich two points have$hich two points have

thethe sa"esa"e potential4potential4

)% ' and (

2% 9 and ,

.% 9 and !

/% ( and ,

5% no pair

'

(

9 !,$

r

$ " !

ConcepTest 17.6 ConcepTest 17.6 ,6uipotential of Point (harge,6uipotential of Point (harge

;ollowup:;ollowup: $hich point has the s"allest potential4 $hich point has the s"allest potential4



$hich re6uires the ost wor"

to "ove a positive charge fro"

P to points ) 2 . or / 4 'll

points are the sa"e distance

fro" P

)% P )

2% P 2

.% P .

/% P /

5% all re6uire the sa"ea"ount of work

P )

2

.

E

/

ConcepTest 17.7aConcepTest 17.7a $ork and ,lectric Potential -$ork and ,lectric Potential -



;or path @)path @) you have to push the

positive charge aainst aainst the E field

which is hard to dohard to do 9y contrast

path @/ is the easiest since the

field does all the work

$hich re6uires the ost wor"

to "ove a positive charge fro"



fro" P

)% P )

2% P 2

.% P .

/% P /


P )

2

.

E

/

ConcepTest 17.7aConcepTest 17.7a $ork and ,lectric Potential -$ork and ,lectric Potential -



$hich re6uires /ero wor" to

"ove a positive charge fro"



fro" P

)% P )

2% P 2

.% P .

/% P /


P )

2

.

E

/

ConcepTest 17.7bConcepTest 17.7b $ork and ,lectric Potential --$ork and ,lectric Potential --



;or path @.path @. you are "oving in a

direction perpendicular to the field

lines This "eans you are "oving

along an e6uipotential which

re6uires no work #by definition%

$hich re6uires /ero wor" to

"ove a positive charge fro"



fro" P

)% P )

2% P 2

.% P .

/% P /


P )

2

.

E

/

ConcepTest 17.7bConcepTest 17.7b $ork and ,lectric Potential --$ork and ,lectric Potential --

;ollowup:;ollowup: $hich path re6uires the least work4 $hich path re6uires the least work4



(apacitor(apacitor C C 11 is connected acrossis connected across

a battery ofa battery of 5 B5 B 'n identical 'n identical

capacitorcapacitor C C # # is connected acrossis connected across

a battery ofa battery of )0 B)0 B $hich one has $hich one has

the "ost charge4the "ost charge4

)% C C 11

2% C C # #

.% both have the sa"e charge

/% it depends on other factors

–

ConcepTest 17.0 ConcepTest 17.0 (apacitors(apacitors



Since $ $ 88 C ! C ! and the two capacitors are

identical the one that is connected to the

greater voltagegreater voltage has the "ost charge"ost charge

which is C C # # in this case

(apacitor(apacitor C C 11 is connected acrossis connected across

a battery ofa battery of 5 B5 B 'n identical 'n identical

capacitorcapacitor C C # # is connected acrossis connected across

a battery ofa battery of )0 B)0 B $hich one has $hich one has

the "ost charge4the "ost charge4

)% C C 11

2% C C # #

.% both have the sa"e charge

/% it depends on other factors

–

ConcepTest 17.0 ConcepTest 17.0 (apacitors(apacitors



)% increase the area of the platesincrease the area of the plates

2% decrease separation between the platesdecrease separation between the plates

.% decrease the area of the plates

/% either #)% or #2%

5% either #2% or #.%

$hat "ust be done to$hat "ust be done to

a capacitor in order toa capacitor in order to

increase the a"ount ofincrease the a"ount of

charge it can hold #forcharge it can hold #for

a constant voltage%4a constant voltage%4

–

ConcepTest 17.aConcepTest 17.a Barying (apacitance -Barying (apacitance -



Since $ = C ! $ = C ! in order to increase the charge

that a capacitor can hold at constant voltage

one has to increase its capacitanceincrease its capacitance Since thecapacitance is given by that can be

done by either increasingincreasing A A or decreasingdecreasing d d

)% increase the area of the platesincrease the area of the plates

2% decrease separation between the platesdecrease separation between the plates

.% decrease the area of the plates

/% either #)% or #2%

5% either #2% or #.%

d

AC 0

$hat "ust be done to$hat "ust be done to

a capacitor in order toa capacitor in order to

increase the a"ount ofincrease the a"ount of

charge it can hold #forcharge it can hold #for

a constant voltage%4a constant voltage%4

–

ConcepTest 17.aConcepTest 17.a Barying (apacitance -Barying (apacitance -



–

' parallelplate capacitor' parallelplate capacitor

initially has a voltage ofinitially has a voltage of /00 B/00 B

andand stays connected to thestays connected to the

battery battery -f the plate spacing is -f the plate spacing is

nownow doubleddoubled what happens4what happens4

)% the voltage decreasesthe voltage decreases

2% the voltage increasesthe voltage increases

.% the charge decreasesthe charge decreases

/% the charge increasesthe charge increases

5% both voltage and charge changeboth voltage and charge change

ConcepTest 17.bConcepTest 17.b Barying (apacitance --Barying (apacitance --



Since the battery stays connected theSince the battery stays connected the

voltage "ust re"ain constant Cvoltage "ust re"ain constant C Since

when the spacing d is

doubled the capacitance C is halved

'nd since $ $ 88 C ! C ! that "eans the

charge "ust decreasecharge "ust decrease

–

d

AC 0

' parallelplate capacitor' parallelplate capacitor

initially has a voltage ofinitially has a voltage of /00 B/00 B

andand stays connected to thestays connected to the

battery battery -f the plate spacing is -f the plate spacing is

nownow doubleddoubled what happens4what happens4

)% the voltage decreasesthe voltage decreases

2% the voltage increasesthe voltage increases

.% the charge decreasesthe charge decreases

/% the charge increasesthe charge increases

5% both voltage and charge changeboth voltage and charge change

ConcepTest 17.bConcepTest 17.b Barying (apacitance --Barying (apacitance --

;ollowup:;ollowup: How do you increase the charge4 How do you increase the charge4



' parallelplate capacitor initially has' parallelplate capacitor initially has

a potential difference ofa potential difference of /00 B/00 B and isand is

then disconnected fro" the chargingthen disconnected fro" the chargingbattery -f the plate spacing is nowbattery -f the plate spacing is now

doubleddoubled #without changing#without changing $ $ % what% what

is the new value of the voltage4is the new value of the voltage4

)% )00 B)00 B

2% 200 B200 B

.% /00 B

/% D00 B

5% )E00 B

–

ConcepTest 17.c ConcepTest 17.c Barying (apacitance ---Barying (apacitance ---



?nce the battery is disconnected?nce the battery is disconnected $ $ has tohas to

re"ain constantre"ain constant since no charge can flow

either to or fro" the battery Since

when the spacing d is

doubled the capacitance C is halved 'nd

since $ $ 88 C ! C ! that "eans the voltage "ustvoltage "ust

doubledouble

' parallelplate capacitor initially has' parallelplate capacitor initially has

a potential difference ofa potential difference of /00 B/00 B and isand is

then disconnected fro" the chargingthen disconnected fro" the chargingbattery -f the plate spacing is nowbattery -f the plate spacing is now

doubleddoubled #without changing#without changing $ $ % what% what

is the new value of the voltage4is the new value of the voltage4

)% )00 B)00 B

2% 200 B200 B

.% /00 B

/% D00 B

5% )E00 B

–

d AC 0

ConcepTest 17.c ConcepTest 17.c Barying (apacitance ---Barying (apacitance ---

unit 17 conceptual review

Documents