1) A section of straight wire within a magnetic field is conducting a current to
ID: 1437646 • Letter: 1
Question
1) A section of straight wire within a magnetic field is conducting a current to the right. The external magnetic field is uniform and directed into the paper.
A number of changes to the initial force are described in (T), (W), (X), (Y), (Z) below. Choices (i)-(vii) are the possible causes of the change in the force.
This change could be caused by:
(i) increasing the current.
(ii) decreasing (but not to zero) the current.
(iii) reversing the direction of current.
(iv) increasing the strength of the magnetic field.
(v) decreasing (but not to zero) the strength of the magnetic field.
(vi) reversing the direction of the magnetic field.
(vii) none of these.
Each change below refers to the initial situation described above:
(T) The magnetic force on the wire is larger and in the same direction.
(W) The magnetic force on the wire is larger and in the opposite direction.
(X) The magnetic force on the wire is smaller and in the same direction.
(Y) The magnetic force magnitude remains the same, but the direction changes.
(Z) The magnetic force on the wire is zero.
Which of the 5 changes listed above ((T), (W), (X), (Y), (Z)) could be caused by more than one of the causes? Choices (i)-(vii) are the possible causes of the changes in the force. Note: do not consider situations where change is produced by two or more of the causes, (i) through (vii), acting simultaneously.
A.) Z
B.) X, W
C.) T, Z
D.) Y, W, Z
E.) T, X, Y
F.) X, W, Z, T
Explanation / Answer
Magnetic force is given by :
F= i(l X B) l: length of wire i: current in the wire B: Magnetic field
Now,
T (The magnetic force on the wire is larger and in the same direction) is caused when either i (increasing the current) or iv ( increasing the strength of the magnetic field) or both occours.
X (The magnetic force on the wire is smaller and in the same direction) is caused when either ii ( decreasing (but not to zero) the current) or v (decreasing (but not to zero) the strength of the magnetic field) or both occours.
Y(The magnetic force magnitude remains the same, but the direction changes) is caused when either iii(reversing the direction of current) or vi(reversing the direction of the magnetic field).
Hense,
E (T, X, Y) Will be the answer.
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