AP Physics C E and M 12.1 Magnetic Fields Overview

Describe magnetic fields through vector direction, field-line representations, and interactions with moving charges and currents.

[Maximum number: 2]

Figure for Question 12.1 Magnetic Fields question 1 — AP Physics C: Electricity & Magnetism

A solenoid is used to generate a magnetic field. The solenoid has an inner radius a, length $\ell$ , and N total turns of wire. A power supply, not shown, is connected to the solenoid and generates current I, as shown in the figure on the left above. The x-axis runs along the axis of the solenoid. Point P is in the middle of the solenoid at the origin of the x y z-coordinate system, as shown in the cutaway view on the right above. Assume $\ell \gg a$ .

One of the students notes that the horizontal component of the magnetic field of Earth is $2.5 \times 10^{-5} \mathrm{~T}$ .

Is there evidence from the graph that the horizontal orientation of the solenoid affects the measured values for B ? Yes No
Justify your answer.

Would the horizontal orientation of the solenoid affect the calculated value for $R_{S}$ ? Yes No
Justify your answer.

A thin conducting loop of radius b and resistance $R_{L}$ is placed concentric with the solenoid, as shown above. The current in the solenoid is decreased from I to zero over time $\Delta t$ .

LO CNV-8.E.a, SP 2.D
1 point

Is there evidence from the graph that the horizontal orientation of the solenoid affects the measured values for B ? Yes No

Justify your answer.

If the line on the graph does not go through the origin, select "Yes"

For a correct justification

1 point

Example: The horizontal component of Earth's magnetic field will add or subtract from
the magnetic field of the solenoid depending on the orientation of the solenoid.

Alternate Points

Alternate Solution

If the line on the graph does pass through the origin, select "No"

For a correct justification

1 point

Example: Based on the graph, the line passes through the origin, so the magnetic field is
zero when the emf of the power supply is zero, therefore Earth's magnetic field is
not affecting the values of B.

LO CNV-8.E.a, SP 2.E
1 point

Would the horizontal orientation of the solenoid affect the calculated value for $R_{S}$ ? Yes No

Justify your answer.

Select "No"

For a correct justification

1 point

Example: The horizontal component of Earth's magnetic field will not affect the change
in magnetic field as the emf is changed. Therefore, the value for the resistance of the
solenoid will not change.

Figure for Answer to Question 12.1 Magnetic Fields question 1 — AP Physics C: Electricity & Magnetism

A thin conducting loop of radius b and resistance $R_{L}$ is placed concentric with the solenoid, as shown above. The current in the solenoid is decreased from I to zero over time $\Delta t$ .

[Maximum number: 1]

A compass needle is in a uniform magnetic field B with its north-seeking pole pointing in the direction of the field. The net magnetic force on the compass needle is

A

in the direction of B

B

in the direction of -B

C

perpendicular to the plane determined by $\mathbf{B}$ and the needle

D

in the same plane as B and the needle, but perpendicular to the needle

E

zero

Figure for Question 12.1 Magnetic Fields question 2 — AP Physics C: Electricity & Magnetism

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Covered syllabus points

12.1 Magnetic Fields question 1

12.1 Magnetic Fields question 2