ConcepTest 19.3 Magnetic Field

ConcepTest 19.3 ConcepTest 19.3 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 19.3 ConcepTest 19.3 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 19.4a ConcepTest 19.4a Mass Spectrometer IMass Spectrometer Ix x x x x x x x x x x

x

x 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 19.4a ConcepTest 19.4a 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 19.4b ConcepTest 19.4b 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 19.4b ConcepTest 19.4b Mass Spectrometer IIMass Spectrometer II

ConcepTest 19.6a ConcepTest 19.6a 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

4) into the page4) into the page

5) out of the page5) out of the page

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 19.6a ConcepTest 19.6a Magnetic Force on a Wire IMagnetic Force on a Wire I1) left1) left

2) right2) right

3) zero3) zero



B

I




on the wire?on the wire?

B

I

1) left1) left

2) right2) right

3) zero3) zero



ConcepTest 19.6b ConcepTest 19.6b Magnetic Force on a Wire IIMagnetic Force on a Wire II




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 19.6b ConcepTest 19.6b Magnetic Force on a Wire IIMagnetic Force on a Wire II




on the wire?on the wire?

ConcepTest 19.7a ConcepTest 19.7a 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 outwardoutward from the

center of the loop. Thus, the forces of

the opposing segments cancel, so the

net force is zerozero.

ConcepTest 19.7a ConcepTest 19.7a 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 19.7b ConcepTest 19.7b 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 19.7b ConcepTest 19.7b Magnetic Force on a Loop IIMagnetic Force on a Loop II

ConcepTest 19.8a ConcepTest 19.8a 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 19.8a ConcepTest 19.8a 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 19.8b ConcepTest 19.8b Magnetic Field of a Wire IIMagnetic Field of a Wire II

1 2 3

ConcepTest 19.8b ConcepTest 19.8b 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 19.9a ConcepTest 19.9a 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, in which direction will turned on, in which direction will

the force act?the 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 19.9a ConcepTest 19.9a 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, in which direction will turned on, in which direction will

the force act?the 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 19.9b ConcepTest 19.9b 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 19.9b ConcepTest 19.9b 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 19.10 ConcepTest 19.10 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 19.10 ConcepTest 19.10 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



Documents

ConcepTest 19.3 Magnetic Field