12.1
Which way do field lines point outside of a magnet?
North to South
What rule can be used to find the direction of a magnetic field?
Right-Hand Rule
When is the magnetic force maximized on a current-carrying wire?
When it is perpendicular to the magnetic field
Two wires are in an identical magnetic field. Wire 1 has a length 1m and velocity 0.5m/s. Wire 2 has a length 1m and velocity 2m/s.
Which wire has a greater electromotive force?
Wire 2.
ϵ= Blv
Wire 1 ϵ= B(1)(.5) = 0.5B
Wire 2 ϵ= B(1)(2)= 2B
Which way do field lines point inside a magnet?
South to North
When the velocity is parallel to the magnetic field, what happens to the magnetic force?
If two parallel wires have currents running in the same direction, where will the forces between them push them?
Towards each other
A loop is entering a magnetic field pointed inside the page. What direction does the induced magnetic field point?
Out of the page
When a magnetic field is added, the domains in a material align. When the field is removed, they revert. What type of material is this?
Paramagnetic
A proton moves through space with a velocity directed eastward. A physicist wants to determine the magnetic field at a point located directly north of the proton's current position. What vector should the physicist use to help apply the right-hand rule?
A. Vector from proton to point
B. Vector perpendicular to both
C. Vector parallel to velocity
D. Vector from point to proton
A. Vector from proton to point
The position vector is drawn from the proton to the point in space. This vector, combined with the velocity vector, decides both the direction and magnitude of the field.
What happens to the magnetic field at a point when the distance between the wire and the point increases?
The magnetic field decreases.
B= (µ0I)/(2πr)
As radius increases, B decreases
A square loop with side length .25m is in a .9T magnetic field. The loop is perpendicular to the field. What is the flux of the loop?
.056 Webers
BcosθA
(.9)(.25)(.25)= .056 Webers
Two wires are both carrying current up towards the top of the page. What is the interaction between these two wires that results from the magnetic fields they create?
Attraction
A wire 1.0 m long carries a current of 5 amps. The wire is at a right angle to a uniform magnetic field. The force on the wire is 0.20N. What is the strength of the magnetic field?
F = ILBsinx
0.20/(5*1) = 0.04T
A long, straight wire carries a current of 5 amps. Find the magnetic field at a distance of 2 cm from the wire.
B = ((4π *10^-7)(5))/(2π)(0.02) = 5*10^-5T
An electromotive force of 4.5 volts induces a current in a 1m long wire. The wire is moving through a magnetic field with a velocity of .7m/s. What is the strength of the magnetic field?
6.43 T
ϵ= Blv
4.5= B(1)(.7)
B=6.43 T
An proton is traveling through a magnetic field with a velocity of 5.6 m/s. The magnetic field has a magnitude of .2 T.
Assuming the magnetic field and velocity are perpendicular, what is the magnitude of the magnetic force on the charged particle?
1.79 x 10 -19 N
F=qvsinθB
F=(1.6 x 10 -19) (5.6)(.2)
=1.79 x 10 -10
An electron (q = -1.6*10^-19C) moves with speed 3*10^6 m/s perpendicular to a magnetic field of strength 2*10^-3T. Find the radius of its circular path.
r = mv/qB (derived from magnetic force and centripetal force equations)
m = 9.11*10^-31
r = ((9.11*10^-31)(3*10^6))/((1.6*10^-19)(2*10^-3))
r = 8.5*10^-3 = 8.5 mm
A coil with 100 turns experiences a change in magnetic flux of 0.05 Wb over 0.10 s. What is the induced EMF?
Use Lenz's law and multiply it by the number of turns
Emf = -100*(0.05/0.10) = -50v
The direction of the EMF opposes the change in magnetic flux.
A 0.40 m wide and 0.80 m long rectangular loop of wire is oriented perpendicular to a uniform magnetic field of 0.50T. What is the magnetic flux through the loop?
(0.40)(0.80)(0.50) = 0.16 Wb