Physics 2.6: Magnetic Fields

Question 1

magnetic field

Answer 1

set up by

• the movement of individual charges (electron moving through space)
• ** the mass movement of charge in the form of a current though a conductive material (such as a copper wire) **
• or*
• the “ flow” of charge in permanent magnets.

spacing between magnetic field lines is reflective of the strength of the field at that point in space: The farther out from the moving charge, the weaker the magnetic field, and the further apart the field lines will be spaced.

At any point along a field line, the magnetic field vector itself is tangential to the line

Question 2

SI Unit for Magnetic Field

Answer 2

• tesla (T) for which 1 T = 1 N· s/m· C.
• gauss, for which 1 T = 10⁴gauss.

Question 3

Diamagnetic materials

Answer 3

• made of atoms with no unpaired electrons and that have no net magnetic field.
• repelled by either pole of a bar magnet (can be called weakly antimagnetic).

In layperson terms, diamagnetic materials are “ nonmagnetic” and include common materials that you wouldn’t ever expect to get stuck to a magnet: wood, plastics, water, glass, and skin,

Question 4

paramagnetic

Answer 4

• become weakly magnetized in the presence of an external magnetic field
• →causes the permanent magnetic dipoles of the individual atoms to align with the external field.
• Paramagnetic materials will be attracted toward the pole of a bar magnet (sometimes called weakly magnetic.)
• Upon removal of the external magnetic field, the thermal energy of the individual atoms will cause the individual magnetic dipoles to reorient randomly, and the material will cease to be magnetized.
• Examples: aluminum, copper, and gold.

Question 5

ferromagnetic materials

Answer 5

• have unpaired electrons and permanent atomic magnetic dipoles that are normally oriented randomly so that the material has no net magnetic dipole
• will become strongly magnetized when exposed to a magnetic field or under certain temperatures

Question 6

Curie temperature

Answer 6

critical temperature for ferromagnetic materials:

above which the material is paramagnetic but below which the material is magnetized as a result of a high degree of alignment of the magnetic fields of the individual atoms (which are assembled into large groups of atoms [10¹²-10¹⁸] called magnetic domains).

When the ambient temperature (i.e., room temperature) is below the Curie temperature, the material is permanently magnetized.

Question 7

Fundamentals of Spin

Answer 7

Question 8

CURRENT-CARRYING WIRES

Answer 8

configuration of the magnetic field lines surrounding a current-carrying wire will depend on the shape of the wire

• straight-wire vs.
• loop

Question 9

Electric current

Answer 9

i=Δq/Δt

magnitude of the current i is the amount of charge Δ q passing through the conductor per unit time Δ t,

Question 10

ampere

Answer 10

SI unit of current

(1 A = 1 coulomb/second)

point of lower electric potential to a point of higher electric potential (and in doing so reduce their electrical potential energy).

By convention, however, the direction of current is the direction in which positive charge would flow from higher potential to lower potential. Thus, the direction of current is opposite to the direction of actual electron flow

Question 11

straight current-carrying wire,

Answer 11

calculate the magnitude of the magnetic field produced by the current i in the wire at a perpendicular distance, r, from the wire

Question 12

Magnetic field (B)

Answer 12

B=µ_oi/2πr

calculate the magnitude of the magnetic field produced by the current i in the wire at a perpendicular distance, r, from the wire

B is the magnetic field at a distance r from the wire, and μ o is the permeability of free space (4π × 10− 7 tesla · meter/ampere = 1.26 × 10− 6 T · m/A).

NOTE: inverse relationship between the magnitude of the magnetic field and the distance from the current.

Question 13

B of Circular loop of current-carrying wire

Answer 13

ONLY gives magnitude of the magnetic field at the center of the cirular loop of the current carrying wire with radius r

B=µ_oi/2r

• Units: T=[(Tm/A)(A)]/m*
  (note: does not inlcude π)

Question 14

Magnetic Field Force

Answer 14

force exerted on a charge moving in a magnetic field:

F=qvBsinθ

Question 15

F_B and F_C

Answer 15

F=qvB=mv²/r

r=mv/qB

B=mv/qr

v=qrB/m

Question 16

Which way does a positively charged particle orbit in a mangetic field if field is going INTO the page?

Negatively charged?

Answer 16

With B Ⓧ

+p: counterclockwise

-p: clockwise

Question 17

FORCE ON CURRENT-CARRYING WIRE

Answer 17

F=iLBsinθ

Units: N=AmT=(C/s)(m)(Ns/mC)

Question 18

Electron volt to Joules conversion

Answer 18

1 electron volt (eV) = 1.60217657 × 10^-19 joules

(aka: the charge of a proton)