The Final Round

Kleenexavailable in

departmentaloffice

PHYS 115 EXAM Friday, Dec 14 10:30-11:20pm

Brace 211Brace 201Ferg 112

One more time:

While the final exam meets:

PHYS 115 FINAL Friday, Dec 21

10:00-noon

Brace 211Brace 201

Brace 113N

Question 1

Your home water heateris rated at 4800 Watts for120 volt electrical service.

How much current does the heater draw?

A. Amp 3

1

)120(

48002 =

B. Amp 30480

)120( 2

=

C. Amp 40120

4800 =

Question 2

Your home water heateris rated at 4800 Watts for120 volt electrical service.

It draws 40-A of current.

A.

Ω= 40120

4800

B.

Ω= 3

1

120

40

C.

Ω= 340

120

What is its total resistance?

Ω= 12040

4800D.

This bar magnet is centered at the origin of a set of axes (+x points to the right, +y into the screen, and +z up toward the top of the page).P, Q, and R are points along each axis.

x

y

zP

R

Q

The magnetic field points ___ at position P.

1. left (-x) 2. right (+x) 3. in (+y)4. out (-y) 5. up (+z) 6. down (-z)

Question 3

This bar magnet is centered at the origin of a set of axes (+x points to the right, +y into the screen, and +z up toward the top of the page).P, Q, and R are points along each axis.

x

y

zP

R

Q

The magnetic field points ___ at position R.

1. left (-x) 2. right (+x) 3. in (+y)4. out (-y) 5. up (+z) 6. down (-z)

Question 4

This bar magnet is centered at the origin of a set of axes (+x points to the right, +y into the screen, and +z up toward the top of the page).P, Q, and R are points along each axis.

x

y

zP

R

Q

The magnetic field points ___ at position Q.

1. left (-x) 2. right (+x) 3. in (+y)4. out (-y) 5. up (+z) 6. down (-z)

Question 5

This solenoid is centered at the origin of a set of axes (+x points to the right, +y into the screen, and +z up toward the top of the page).P, Q, and R are points along each axis.

x

yI Iz

P

R

Q

Question 6

The magnetic field points ___ at position R.

1. left (-x) 2. right (+x) 3. in (+y)4. out (-y) 5. up (+z) 6. down (-z)

This solenoid is centered at the origin of a set of axes (+x points to the right, +y into the screen, and +z up toward the top of the page).P, Q, and R are points along each axis.

x

yI Iz

P

R

Q

Question 7

The magnetic field points ___ at position P.

1. left (-x) 2. right (+x) 3. in (+y)4. out (-y) 5. up (+z) 6. down (-z)

This solenoid is centered at the origin of a set of axes (+x points to the right, +y into the screen, and +z up toward the top of the page).P, Q, and R are points along each axis.

x

yI Iz

P

R

Q

Question 8

The magnetic field points ___ at position Q.

1. left (-x) 2. right (+x) 3. in (+y)4. out (-y) 5. up (+z) 6. down (-z)

Each figure below is a source of a magnetic field.

For which, at its center, does that magnetic field point along the

negative x direction (left)?

+ xx

Question 9

The south pole of a bar magnetapproaches this conducting loopfrom behind. This induces

A. a clockwise current in the loop.B. a counterclockwise current in the loop.C. no current in the loop.

Question 10

A magnet dropped from high above, fallsthrough a wire loop, its North-pole first.

As the N-pole approachesthe loop from above, thecurrent generated in it, viewed from above will

An induced current in theloop sets up a field of itsown that exerts a force

on the bar magnet.

A. flow clockwise. B. flow counterclockwise.C. flow toward the magnet.D. flow away from the magnet.E. be zero.

Question 11

A magnet dropped from high above, fallsthrough a wire loop, its North-pole first.

As the N-pole approachesthe loop from above, the

force between the barmagnet and the loop

will be

An induced current in theloop sets up a field of itsown that exerts a force

on the bar magnet.

A. attractive.B. repulsive.C. zero.

Question 12

A magnet dropped from high above, fallsthrough a wire loop, its North-pole first.

The moment the bar reaches halfway through theloop, the current atthat instant will be

A. flow clockwise. B. flow counterclockwise.C. flow toward the magnet.D. flow away from the magnet.E. be zero.

Question 13

A magnet dropped from high above, fallsthrough a wire loop, its North-pole first.

The moment the bar reaches halfway through theloop, the current atthat instant will be

A. flow clockwise. B. flow counterclockwise.C. flow toward the magnet.D. flow away from the magnet.E. be zero.

Question 13

A magnet dropped from high above, fallsthrough a wire loop, its North-pole first.

As the S-pole dropsaway from loop,

the current generated within it, viewed from

above will

A. flow clockwise. B. flow counterclockwise.C. flow toward the magnet.D. flow away from the magnet.E. be zero.

Question 14

+-

When the switch is closed, the sudden influx of magnetic field induces a

current in the metal ring which

A. attracts the ring to the loop. B. repels the ring from the loop. C. neither attracts nor repels the ring.

A coil is connected through an open switch to a battery. A thin metallic ring

lies below the coil. Initially no current is drawn from the battery.

Question 15

+-

Once the switch is closed and steady current is established through the loop,

the ring is

A. attracted to the loop. B. repelled from the loop. C. neither attracted nor repeled.

A coil is connected through an open switch to a battery. A thin metallic ring

lies below the coil. Initially no current is drawn from the battery.

Question 16

I

The “Lorentz Force”

A conducting rod is drawndown through the B-field

as shown.

Free electronsin the rod will 1) flow through the hand to ground.2) tend to bunch up at the far end.3) be pushed to upper surface of the rod.4) be unaffected.

Question 17

Which one of the following items emits radio waves?

(A) A stationary, vertical and uniformly charged metal flagpole.

(B) A uniformly charged plastic stick spinning end-over-end in the air.

(C) A stationary, horizontal uniformly charged metal flagpole.

(D) A stationary loop of wire with a steady electric current flowing through it.

Question 18

Charge vibrates linearly along the direction illustrated. This oscillation emits transverse waves preferentially in what direction?

Waves are transmitted equally in all directions

Question 19

E field points down

E field points up

E field momentarily zero

strong

weak

zero

E-fieldpointingdown

The magnetron of a microwave horn

generates a horizontally varying B-field and

oscillating vertical E-field. We found which of the

aluminum gratings below allows the microwaves

To pass?

1

2

Question 20

Lecture 40: 20 Final Questions!Question: 1. C P = IV I = P/V = 4800/120 = 40 Amp 2. B V = IR R=V/I = 120/40 = 3 Ω or P=V2/R R=V2/P 3. 6 down, field lines point into the South pole 4. 5 up – the field lines double back, along the sides 5. 5 up – this side no different from above 6. 2 the right-hand-rule should place your thumb at this end 7. 1 like a bar magnet, field lines run back parallel with the magnet

8. 1 same as 5 above. 9. C a and b involve negatively charged electrons10. B the S-pole introduces flux pointing into the page. To compensate the loop produces a counterclockwise current generating its own flux out of the page.

11. B To produce flux directed upward against the magnet’s.12. B Repulsive. An N-pole faces up at the falling N-pole.13. E There is no increase in flux through the loop as the middle of the magnet (where field lines are sparse and parallel with the magnet) moves past.

14. A Now flux is vanishing and must be replaced.15. B The opposing magnetic field induced, points an N-pole up.16. C Steady current no changing magnetic field no induced current.17. 2 Positive charge collects near the hand, free electrons are pushed to the far end.

18. B The twirling rod is the only moving charge.19. 4 Like transmitting antenna, the traveling E-fields are to the oscillating current.20. 2 Receiving antenna, parallel with the E-field that drives current, will absorb the transited energy. A grid perpendicular to that will let the energy pass.

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