Answer Key
Magnetism Review Key
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University:
Jackson College -
Course:
PHY-232 | College Physics II Academic year:
2022
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Views:
88
Pages:
19
Author:
Jordyn Perkins
Textual Content:
Magnetism Review
1. An electric current flows through a solenoid as shown below.
solenoid with current flowing
What is the direction of the magnetic field inside the solenoid?
Right Hand Rule (RHR):
Thumb = current
Fingers curl inside left to right
Answer: B
2. A long conductor is placed in a 0.65T magnetic field as shown below.
conductor in a magnetic field
What are the magnitude and direction of the current that produces a 1.6N force on the wire directed up the page?
RHR:
Palm up (F)
Fingers in the page (B)
Thumb points to the right (I)
Calculation:
F = BIL
I = F / (BL)
I = 1.6N / (0.65T * 0.35m)
I = 7.3A (right)
Answer: Right
3. A proton has a speed of 5.0x10^6 m/s while traveling perpendicular to a 0.147T magnetic field. What is the magnetic force on the proton?
F = qvB
F = (1.6x10^-19 C)(5.0x10^6 m/s)(0.147T)
F = 1.1x10^-13 N
Answer: 1.1x10^-13 N
4. The flux through a circular coil with a radius of 0.075m is 0.013Wb when placed perpendicular to a magnetic field. What is the strength of the magnetic field?
Φ = BA
B = Φ / A
B = 0.013Wb / (π(0.075m)^2)
B = 0.74T
Answer: 0.74T
5. The diagram below shows an aluminum ring and the current induced in it by the nearby magnet that is free to move along its central axis.
aluminum ring with a magnet moving towards it
The magnet must be:
A. stationary
B. moving to the left
C. moving to the right
D. spinning about its central axis
Explanation:
According to Lenz's law, the direction of the induced current is such that it opposes the change in magnetic flux. As the magnet moves towards the ring, the magnetic flux through the ring increases. To oppose this increase, the induced current in the ring will create a magnetic field that repels the approaching magnet. This can only be achieved if the current flows in a direction such that the induced magnetic field opposes the increasing external magnetic field. This requires the magnet to be moving to the right.
6. A loop of wire of area 0.32 m² is placed in a 0.75 T magnetic field as shown. The magnetic field is changed to 0.35 T in the opposite direction in 0.45 s.
loop of wire in a magnetic field
What are the magnitude and direction of the current through the 15 Ω resistor?
Calculation:
Induced EMF:
E = -N(ΔΦ/Δt)
= -(0.35 - 0.75)(0.32) / 0.45
= 0.284 V
Current:
I = E/R
= 0.284 V / 15 Ω
= 0.019 A
Direction of current:
Using Lenz's law, the induced current will flow in a direction such that it opposes the change in magnetic flux. Since the magnetic field is decreasing, the induced current will flow in a direction to maintain the original magnetic field. Using the right-hand rule, we can determine that the current will flow clockwise through the resistor.
Answer:
Magnitude: 0.019 A
Direction: Clockwise
A charged particle travels in a circular path in a magnetic field. What changes to the magnetic field and to the velocity of the particle would both cause the radius of its path to decrease?
CHANGE TO THE MAGNETIC FIELD CHANGE TO THE VELOCITY
A. Increase Increase
B. Increase Decrease
C. Decrease Increase
D. Decrease Decrease
Explanation:
The radius of the circular path of a charged particle in a magnetic field is given by:
r = mv / (qB)
Where:
r is the radius of the path
m is the mass of the particle
v is the velocity of the particle
q is the charge of the particle
B is the magnetic field strength
To decrease the radius, we can either decrease the velocity (v) or increase the magnetic field strength (B). Therefore, option D is correct.
The diagram below shows two coils in a magnetic field.
two coils, one perpendicular and one parallel to a magnetic field
An electric current can be induced in the coil oriented with its plane:
A. Parallel to a constant magnetic field
B. Parallel to a changing magnetic field
C. Perpendicular to a constant magnetic field
D. Perpendicular to a changing magnetic field
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