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B2-0:
A current-carrying wire is in a B-field. The wire is parallel to the
B-field as shown. What is the direction of the magnetic force on
the wire?
A) right
these.
B) left
B
I
`
C) up
D) down E) None of
More B-field Concept Tests
B2-1.
Which point A or B has the larger magnetic field?
A
B
C : The B-field is the same at A and B.
I
I
B
A
B2-2.
A long straight wire is carrying current I. The magnetic field at
point x has magnitude Btotal.
Btotal
x
r
I
B1/2 =?
r

True (A) or False (B): The magnetic field B1/ 2 at point x due only
to the current to the left
of x points in the same direction and has

1/2 the magnitude of Btotal .
B2-3.
A rectangular loop of wire is carrying a current i in the clockwise direction
and is near a long straight wire carrying a current I, as shown. What is the
direction of the net force on the rectangular loop, due to the B-field from the
long, straight wire.
I
A
i
B
D
C
E: Net force is zero.
B2-4. A long straight copper wire has radius b and carries a constant current
of magnitude I. The current density of magnitude J=I/(b2) is uniform
throughout the wire. What is the current contained in the circular loop £,
with radius r < b, centered on the wire's center as shown?
2
r
r
I
I
A:
B:
b
b
b
F
IJ
G
HK
F
IJ
G
HK
Fr I
C: GJ I
Hb K
3
r
J = constant
D: None of these
How does the magnitude of the B-field a distance r < b from the center of
the wire depend on r?
A: B  r
B: B = constant
C: B  1/r
D: B  1/r2
E: None of these/don't know.
Referring to the same wire, for the new loop £ shown below, what is the
r r
B
value of ò
Ñ ×d l ?
L
A: +I/2
b
B: > I/2
C: < I/2
J = constant
B2-0b
How do the two angles  and  in the diagram below compare?

r

I
dl
A)  = 
x
x
B)  = + 90o
D)  =
C)  =
E) None of these!
B2-5. Three long straight solenoids all of length L and all with the same
(large) number of closely-packed turns N, all with the same current I, have
different cross-sections as shown.
A
Which solenoid has the largest field B at
its center?
B
C
D: All three have the same field B.
True(A) or False(B): All three solenoids have uniform B-fields in their
interiors.
B2-6. A magnetic compass is placed at the points A, B, and C near an
electric circuit which has the following twisty shape:
A
B
C
The deflection of the compass needle is a measure of the strength of the
magnetic field. The relative deflection of the needle n order from biggest to
smallest deflection is..
A: ABC
D: ACB
B: CBA
C: BCA
E: None of these.
B2-7. A permanent bar magnet is broken in half. The two pieces are
interchanged, keeping their orientations fixed, as shown below. Do the
pieces attract or repel?
A: Attract
B: Repel
2
1
2
1
C: Neither! There is no net force.
B2-8.A row of positive charges is stationary on the ground. A person with
a gauss-meter(which measures the magnetic field) is running to the right
along the row of charges, at the same height as the charges and in front of
them (in the diagram below). What is the direction of the B-field which the
observer measures?
+
+
+
+
+
+
Pink(up)
+
Blue
(backward
direction)
Yellow
(forward direction)
Green(down)
Purple: Zero
B2-9.
A toroidal coil has N turns total. The current direction is indicated in the
figure.