ConcepTest PowerPoints Chapter 20 Physics: Principles …jgladden/phys214/handouts/ConcepTe... · ConcepTest PowerPoints Chapter 20 Physics: Principles with Applications, 6th edition

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ConcepTest PowerPoints

Chapter 20

Physics: Principles with Applications, 6th edition

Giancoli

ConcepTest 20.1a ConcepTest 20.1a Magnetic Force IMagnetic Force I

1) out of the page1) out of the page

2) into the page2) into the page

3) downwards3) downwards

4) to the right4) to the right

5) to the left5) to the left

A positive charge enters a A positive charge enters a

uniform magnetic field as uniform magnetic field as

shown. What is the direction shown. What is the direction

of the magnetic force?of the magnetic force?

x x x x x x x x x x x x


x x x x x xx x x x x x

vv

qq

Using the right-hand rule, you can

see that the magnetic force is

directed to the leftto the left. Remember

that the magnetic force must be

perpendicularperpendicular to to BOTHBOTH the the BB field field

and the velocityand the velocity.

ConcepTest 20.1a ConcepTest 20.1a Magnetic Force IMagnetic Force I












x x x x x xx x x x x x

vv

qqFF




4) upwards4) upwards




x x x x x xx x x x x xvvqq

ConcepTest 20.1b ConcepTest 20.1b Magnetic Force IIMagnetic Force II







directed upwardsupwards. Remember







4) upwards4) upwards




x x x x x xx x x x x xvvqq

FF

ConcepTest 20.1b ConcepTest 20.1b Magnetic Force IIMagnetic Force II







3) zero3) zero



→ → → → →→ → → → →

→ → → → →→ → → → →

→ → → → →→ → → → →

→ → → → →→ → → → →

vv

qq

ConcepTest 20.1c ConcepTest 20.1c Magnetic Force IIIMagnetic Force III







directed into the pageinto the page. Remember






3) zero3) zero



→ → → → →→ → → → →

→ → → → →→ → → → →

→ → → → →→ → → → →

→ → → → →→ → → → →

vv

qqFF ××

ConcepTest 20.1c ConcepTest 20.1c Magnetic Force IIIMagnetic Force III





↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑↑

↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑

↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑↑

↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑

vv

qq



3) zero3) zero



ConcepTest 20.1d ConcepTest 20.1d Magnetic Force IVMagnetic Force IV





The charge is moving parallel to parallel to

the magnetic fieldthe magnetic field, so it does not it does not

experience any magnetic forceexperience any magnetic force.

Remember that the magnetic force

is given by: F = v B sin(θ ) .

↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑↑

↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑

↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑↑

↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑

vv

qq

FF = 0 = 0



3) zero3) zero



ConcepTest 20.1d ConcepTest 20.1d Magnetic Force IVMagnetic Force IV





ConcepTest 20.2 ConcepTest 20.2 Atomic BeamsAtomic Beams







1

2

34

A beam of atoms enters A beam of atoms enters

a magnetic field region. a magnetic field region.

What path will the What path will the

atoms follow?atoms follow?

Atoms are neutralneutral objects whose net charge is zerozero.

Thus they do not experience a magnetic force.

ConcepTest 20.2 ConcepTest 20.2 Atomic BeamsAtomic Beams







1

2

34

A beam of atoms enters A beam of atoms enters

a magnetic field region. a magnetic field region.

What path will the What path will the

atoms follow?atoms follow?

Follow-up:Follow-up: What charge would follow path #3? What about path #1? What charge would follow path #3? What about path #1?

ConcepTest 20.3 ConcepTest 20.3 Magnetic FieldMagnetic Field

xx

yy

A proton beam enters into a A proton beam enters into a

magnetic field region as shown magnetic field region as shown

below. What is the direction below. What is the direction

of the magnetic field of the magnetic field BB? ?

1) + 1) + yy

2) 2) –– yy

3) +3) + x x

4) + 4) + zz (out of page) (out of page)

5) 5) –– zz (into page) (into page)

The picture shows the force acting

in the ++yy direction direction. Applying the

right-hand rule leads to a B field

that points into the pageinto the page. The B

field must be out of the planeout of the plane

because B B ⊥⊥ v v and B B ⊥⊥ F F.

ConcepTest 20.3 ConcepTest 20.3 Magnetic FieldMagnetic Field

xx

yy

A proton beam enters into a A proton beam enters into a

magnetic field region as shown magnetic field region as shown

below. What is the direction below. What is the direction

of the magnetic field of the magnetic field BB? ?

1) + 1) + yy

2) 2) –– yy

3) + 3) + xx


5) 5) –– zz (into page) (into page)

Follow-up:Follow-up: What would happen to a beam of atoms? What would happen to a beam of atoms?

ConcepTest 20.4a ConcepTest 20.4a Mass Spectrometer IMass Spectrometer Ix x x x x x x x x x x

x






1 2

Two particles of the Two particles of the same masssame mass

enter a magnetic field with the enter a magnetic field with the

same speedsame speed and follow the paths and follow the paths

shown. Which particle has the shown. Which particle has the

bigger chargebigger charge? ?

3) both charges are equal

4) impossible to tell from the picture

The relevant equation for us is:

According to this equation, the

bigger the charge, the smaller the radius.

ConcepTest 20.4a ConcepTest 20.4a Mass Spectrometer IMass Spectrometer Ix x x x x x x x x x x

x






1 2

qB

mvR =

Two particles of the Two particles of the same masssame mass

enter a magnetic field with the enter a magnetic field with the

same speedsame speed and follow the paths and follow the paths

shown. Which particle has the shown. Which particle has the

bigger chargebigger charge? ?

3) both charges are equal

4) impossible to tell from the picture

Follow-up:Follow-up: What is the sign of the charges in the picture? What is the sign of the charges in the picture?

1) it increases1) it increases

2) it decreases2) it decreases

3) it stays the same3) it stays the same

4) depends on the velocity direction4) depends on the velocity direction

5) depends on the 5) depends on the BB field direction field direction

A proton enters a uniform A proton enters a uniform

magnetic field that is magnetic field that is

perpendicular to the perpendicular to the

proton’s velocity. What proton’s velocity. What

happens to the happens to the kinetic kinetic

energyenergy of the proton? of the proton?






ConcepTest 20.4b ConcepTest 20.4b Mass Spectrometer IIMass Spectrometer II

The velocity of the proton

changes directiondirection but the

magnitudemagnitude (speed) doesn’t

change. Thus the kinetic kinetic

energy stays the sameenergy stays the same.

1) it increases1) it increases

2) it decreases2) it decreases

3) it stays the same3) it stays the same

4) depends on the velocity direction4) depends on the velocity direction

5) depends on the 5) depends on the BB field direction field direction

A proton enters a uniform A proton enters a uniform

magnetic field that is magnetic field that is

perpendicular to the perpendicular to the

proton’s velocity. What proton’s velocity. What

happens to the happens to the kinetic kinetic

energyenergy of the proton? of the proton?






ConcepTest 20.4b ConcepTest 20.4b Mass Spectrometer IIMass Spectrometer II

ConcepTest 20.5 ConcepTest 20.5 Velocity SelectorVelocity Selector

What direction would a What direction would a BB field field

have to point for a beam of have to point for a beam of

electronselectrons moving to the right to moving to the right to

go go undeflectedundeflected through a region through a region

where there is a uniform where there is a uniform electric electric

fieldfield pointing vertically upward? pointing vertically upward?

1) up (parallel to 1) up (parallel to E E ))

2) down (antiparallel to 2) down (antiparallel to E E ))



5) impossible to accomplish5) impossible to accomplish

electrons

EE

vv

B = ?B = ?

Without a B field, the electrons feel an

electric force downwardsdownwards. In order to

compensate, the magnetic force has to

point upwardsupwards. Using the right-hand

rule and the fact that the electrons are

negatively chargednegatively charged leads to a BB field field

pointing pointing out of the pageout of the page.

ConcepTest 20.5 ConcepTest 20.5 Velocity SelectorVelocity Selector

What direction would a What direction would a BB field field

have to point for a beam of have to point for a beam of

electronselectrons moving to the right to moving to the right to

go go undeflectedundeflected through a region through a region

where there is a uniform where there is a uniform electric electric

fieldfield pointing vertically upward? pointing vertically upward?

1) up (parallel to 1) up (parallel to E E ))

2) down (antiparallel to 2) down (antiparallel to E E ))



5) impossible to accomplish5) impossible to accomplish

electrons

EE

vv

B = ?B = ?

ConcepTest 20.6a ConcepTest 20.6a Magnetic Force on a Wire IMagnetic Force on a Wire I

A horizontal wire carries a current A horizontal wire carries a current

and is in a vertical magnetic field. and is in a vertical magnetic field.

What is the direction of the force What is the direction of the force

on the wire? on the wire?

1) left1) left

2) right2) right

3) zero3) zero



B

I

Using the right-hand rule, we

see that the magnetic force

must point out of the pageout of the page.

Since F must be perpendicular

to both I and B, you should

realize that FF cannot be in the cannot be in the

plane of the page at allplane of the page at all.

ConcepTest 20.6a ConcepTest 20.6a Magnetic Force on a Wire IMagnetic Force on a Wire I



What is the direction of the force on What is the direction of the force on

the wire? the wire?

1) left1) left

2) right2) right

3) zero3) zero



B

I

B

I

1) left1) left

2) right2) right

3) zero3) zero



ConcepTest 20.6b ConcepTest 20.6b Magnetic Force on a Wire IIMagnetic Force on a Wire II



What is the direction of the force What is the direction of the force

on the wire? on the wire?

When the current is parallelparallel to

the magnetic field lines, the force

on the wire is zerozero. B

I

1) left1) left

2) right2) right

3) zero3) zero



ConcepTest 20.6b ConcepTest 20.6b Magnetic Force on a Wire IIMagnetic Force on a Wire II



What is the direction of the force on What is the direction of the force on

the wire? the wire?

ConcepTest 20.7a ConcepTest 20.7a Magnetic Force on a Loop IMagnetic Force on a Loop I

BB

xx

zz

yy

A rectangular current loop is A rectangular current loop is

in a uniform magnetic field. in a uniform magnetic field.

What is the direction of the What is the direction of the

net force on the loop? net force on the loop?

1) + 1) + xx

2) + 2) + yy

3) zero3) zero

4) - 4) - xx

5) - 5) - yy

Using the right-hand rule, we find that

each of the four wire segments will

experience a force outwardsoutwards from the

center of the loop. Thus, the forces

of the opposing segments cancel, so

the net force is zerozero.

ConcepTest 20.7a ConcepTest 20.7a Magnetic Force on a Loop IMagnetic Force on a Loop I

BB

xx

zz

yy

A rectangular current loop is A rectangular current loop is

in a uniform magnetic field. in a uniform magnetic field.


net force on the loop? net force on the loop?

1) + 1) + xx

2) + 2) + yy

3) zero3) zero

4) - 4) - xx

5) - 5) - yy

If there is a current in If there is a current in

the loop in the direction the loop in the direction

shown, the loop will:shown, the loop will:

1) move up1) move up

2) move down2) move down

3) rotate clockwise3) rotate clockwise

4) rotate counterclockwise4) rotate counterclockwise

5) both rotate and move5) both rotate and move

N S

NS

B field out of NorthB field out of NorthB field into SouthB field into South

ConcepTest 20.7b ConcepTest 20.7b Magnetic Force on a Loop IIMagnetic Force on a Loop II

Look at the North Pole: here the

magnetic field points to the rightright and

the current points out of the pageout of the page.

The right-hand rule says that the force

must point upup. At the south pole, the

same logic leads to a downwarddownward force.

Thus the loop rotates clockwiseclockwise.

N S

F

F

1) move up1) move up

2) move down2) move down

3) rotate clockwise3) rotate clockwise

4) rotate counterclockwise4) rotate counterclockwise

5) both rotate and move5) both rotate and move

If there is a current in If there is a current in

the loop in the direction the loop in the direction

shown, the loop will:shown, the loop will:

ConcepTest 20.7b ConcepTest 20.7b Magnetic Force on a Loop IIMagnetic Force on a Loop II

ConcepTest 20.8a ConcepTest 20.8a Magnetic Field of a Wire IMagnetic Field of a Wire I

P1

2

3

4

If the currents in these wires have

the same magnitude, but opposite

directions, what is the direction of

the magnetic field at point P?

1) direction 11) direction 1




5) the 5) the BB field is zero field is zero

Using the right-hand rule, we

can sketch the B fields due

to the two currents. Adding Adding

them up as vectorsthem up as vectors gives a

total magnetic field pointing

downwarddownward.

P

1

2

3

4

ConcepTest 20.8a ConcepTest 20.8a Magnetic Field of a Wire IMagnetic Field of a Wire I

If the currents in these wires have

the same magnitude, but opposite

directions, what is the direction of

the magnetic field at point P?





5) the 5) the BB field is zero field is zero

Each of the wires in the figures below carry the same current, either into or out of the page. In which case is the magnetic field at the center of the square greatest?

1) arrangement 11) arrangement 1



4) same for all4) same for all

1 2 3B=? B=?B=?

ConcepTest 20.8b ConcepTest 20.8b Magnetic Field of a Wire IIMagnetic Field of a Wire II

1 2 3

ConcepTest 20.8b ConcepTest 20.8b Magnetic Field of a Wire IIMagnetic Field of a Wire II

Each of the wires in the figures below carry the same current, either into or out of the page. In which case is the magnetic field at the center of the square greatest?




4) same for all4) same for all

ConcepTest 20.9a ConcepTest 20.9a Field and Force IField and Force I

z

y

x

I+q

A positive charge moves parallel A positive charge moves parallel

to a wire. If a current is suddenly to a wire. If a current is suddenly

turned on, which direction will the turned on, which direction will the

force act?force act?


2) - 2) - zz (into page) (into page)

3) + 3) + xx

4) - 4) - xx

5) - 5) - yy

Using the right-hand rule to determine the

magnetic field produced by the wire, we

find that at the position of the charge +q

(to the left of the wire) the B field points points

out of the pageout of the page. Applying the right-hand

rule again for the magnetic force on the

charge, we find that +q experiences a

force in the +x direction+x direction.

ConcepTest 20.9a ConcepTest 20.9a Field and Force IField and Force I

z

y

x

I+q

A positive charge moves parallel A positive charge moves parallel

to a wire. If a current is suddenly to a wire. If a current is suddenly

turned on, which direction will the turned on, which direction will the

force act?force act?


2) - 2) - zz (into page) (into page)

3) + 3) + xx

4) - 4) - xx

5) - 5) - yy

Two straight wires run parallel to Two straight wires run parallel to

each other, each carrying a each other, each carrying a

current in the direction shown current in the direction shown

below. The two wires experience below. The two wires experience

a force in which direction?a force in which direction?

1) toward each other1) toward each other

2) away from each other2) away from each other

3) there is no force3) there is no force

ConcepTest 20.9b ConcepTest 20.9b Field and Force IIField and Force II

The current in each wire produces a magnetic

field that is felt by the current of the other

wire. Using the right-hand rule, we find that

each wire experiences a force toward the

other wire (i.e., an attractive forceattractive force) when the

currents are parallelcurrents are parallel (as shown).

ConcepTest 20.9b ConcepTest 20.9b Field and Force IIField and Force II

Two straight wires run parallel to Two straight wires run parallel to

each other, each carrying a each other, each carrying a

current in the direction shown current in the direction shown

below. The two wires experience below. The two wires experience

a force in which direction?a force in which direction?

1) toward each other1) toward each other

2) away from each other2) away from each other

3) there is no force3) there is no force

Follow-up:Follow-up: What happens when What happens when one of the currents is turned off?one of the currents is turned off?

ConcepTest 20.10 ConcepTest 20.10 Current LoopCurrent Loop

P

I


magnetic field at the center magnetic field at the center

(point P) of the square loop (point P) of the square loop

of current?of current?

1) left1) left

2) right2) right

3) zero3) zero



Use the right-hand rule for each

wire segment to find that each

segment has its B field pointing

out of the pageout of the page at point P.

ConcepTest 20.10 ConcepTest 20.10 Current LoopCurrent Loop

P

I


magnetic field at the center magnetic field at the center

(point P) of the square loop (point P) of the square loop

of current?of current?

1) left1) left

2) right2) right

3) zero3) zero



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ConcepTest PowerPoints Chapter 20 Physics: Principles …jgladden/phys214/handouts/ConcepTe... · ConcepTest PowerPoints Chapter 20 Physics: Principles with Applications, 6th edition