W10D2

Important Dates

November 11th, 2010Veterans Day

November 25th, 2010Thanksgiving Holiday

December 6th, 2010Last day of classes

December 7th, 2010Final exams begin

December 11, 2010Probable date for 2054 Studio Final (7:30AM ?)

December 16th, 2010 Grades due on myUCF

We continue with magnetism with a study of induction.

Next will be inductors. Following inductors will be the next

examination.

Quiz on Friday Problem Session next Monday

I

I

A

What is the direction of the magneticfield due to these two currents at point A?

A LeftB RightC InD OutE Other direction

Clique

There are “natural” magnets (like a compass) that have a magnetic field associated with them.

Electric Currents produce magnetic fields. Like the field around a wire.

Moving charges in a magnetic field experience forces.

Electric Currents in magnetic fields also experience forces (BiL).

NEXT: CHANGING MAGNETIC FIELDS produce currents in loops of wire. This is called induction and this will be started today.

Chapter 21Sections 1-7

Chapter 22Sections 1-5Sections 8-9

You should have been reading Chapter 21 andshould begin 22 now

A beam of protons moves in a circle of radius 0.25 m. The protons move perpendicular to a 0.20-T magnetic field. (a) What is the speed of each proton?(b) Determine the magnitude of the centripetal force that acts on each proton.

4.79e+06m/s

1.53e-13N

A particle is going around in a circle in a magnetic fieldthat is perpendicular to the plane of the circle with a radius rand a velocity v. If the magnetic field is increased, theradius will:

A increaseB decreaseC remain the sameD explode

When beryllium-7 ions (m = 1.165 10-26 kg) pass through a mass spectrometer, a uniform magnetic field of 0.2503 T curves their path directly to the center of the detector (see figure below). For the same accelerating potential difference, what magnetic field should be used to send beryllium-10 ions (m = 1.663 10-26 kg) to the same location in the detector? Both types of ions are singly ionized (q = +e)

A proton with a speed of 3.63 106 m/s is shot into a region between two plates that are separated by a distance of 0.24 m. As the drawing shows, a magnetic field exists between the plates, and it is perpendicular to the velocity of the proton. What must be the magnitude of the magnetic field so the proton just misses colliding with the opposite plate?

0.158T

Two coils have the same number of circular turns and carry the same current. Each rotates in a magnetic field as in the figure below. Coil 1 has a radius of 5.2 cm and rotates in a 0.13-T field. Coil 2 rotates in a 0.42-T field. Each coil experiences the same maximum torque. What is the radius (in cm) of coil 2?

1 1 1 2 2

23 2 21 1

2 22

22

(sin 0)

(0.052) (0.13)2.6 10

0.42

2.87 10

Max

NIA B NIA B

A BA m r

B

r m

Suppose in the figure that I1 = I2 = 21 A and that the separation between the wires is 0.016 m. By applying an external magnetic field (created by a source other than the wires) it is possible to cancel the mutual repulsion of the wires. This external field must point along the vertical direction.

What is the magnitude of the external field?

D

20

7 70

74

2

4 10 4 10

2 2 2

4 21 102.6 10

2 0.016

I LF BIL

D

I I IB

D D D

B T