AP Physics Multiple Choice Questions on Magnet Fields

📚 Quick Study Guide

• 🧲 Magnetic Field (B) is a vector field that exerts a force on moving electric charges and magnetic dipoles.
• 🧭 The direction of the magnetic field is defined as the direction that the north end of a compass needle points.
• 💪 The force on a moving charge in a magnetic field is given by the Lorentz force: $\vec{F} = q(\vec{v} \times \vec{B})$, where $q$ is the charge, $\vec{v}$ is the velocity, and $\vec{B}$ is the magnetic field.
• 전류가 흐르는 도선이 자기장 내에 놓일 때 받는 힘은 다음과 같습니다: $\vec{F} = I \vec{L} \times \vec{B}$, 여기서 $I$는 전류, $\vec{L}$은 도선의 길이 벡터, $\vec{B}$는 자기장입니다.
• 🔄 The magnetic field due to a long, straight wire is given by $B = \frac{\mu_0 I}{2 \pi r}$, where $\mu_0$ is the permeability of free space, $I$ is the current, and $r$ is the distance from the wire.
• 🌀 The magnetic field inside a solenoid is given by $B = \mu_0 n I$, where $n$ is the number of turns per unit length.
• ⚛️ Magnetic dipole moment ($\mu$) is a measure of the strength of a magnetic source. A current loop has a magnetic dipole moment of $\mu = IA$, where A is the area of the loop.

Practice Quiz

1. A proton is moving with velocity $\vec{v} = (2 \times 10^6 m/s) \hat{i}$ in a magnetic field $\vec{B} = (0.5 T) \hat{k}$. What is the magnitude of the magnetic force on the proton?
   1. 0 N
   2. 1.6 x 10^-13 N
   3. 3.2 x 10^-13 N
   4. 6.4 x 10^-13 N
2. A wire carrying a current of 5 A is placed in a uniform magnetic field of 0.2 T. The length of the wire is 1 m and it is oriented at an angle of 30 degrees with respect to the magnetic field. What is the magnitude of the magnetic force on the wire?
   1. 0.5 N
   2. 1.0 N
   3. 0.866 N
   4. 0.25 N
3. What is the magnetic field at a distance of 0.1 m from a long, straight wire carrying a current of 10 A? ($\mu_0 = 4\pi \times 10^{-7} T \cdot m/A$)
   1. 2 x 10^-5 T
   2. 4 x 10^-5 T
   3. 6 x 10^-5 T
   4. 8 x 10^-5 T
4. A circular loop of wire with radius 0.05 m carries a current of 2 A. What is the magnetic dipole moment of the loop?
   1. 0.0157 A m^2
   2. 0.0314 A m^2
   3. 0.00785 A m^2
   4. 0.0628 A m^2
5. An electron is moving in a circular path of radius 0.1 m in a uniform magnetic field of 1 T. What is the speed of the electron? (mass of electron = 9.11 x 10^-31 kg, charge of electron = 1.60 x 10^-19 C)
   1. 1.76 x 10^11 m/s
   2. 1.76 x 10^8 m/s
   3. 1.76 x 10^6 m/s
   4. 1.76 x 10^4 m/s
6. What is the force on a moving negative charge due to an Electric field?
   1. $\vec{F}=q\vec{E}$
   2. $\vec{F}=-q\vec{E}$
   3. $\vec{F}=q\vec{B}$
   4. $\vec{F}=-q\vec{B}$
7. A solenoid with 1000 turns per meter carries a current of 2 A. What is the magnetic field inside the solenoid? ($\mu_0 = 4\pi \times 10^{-7} T \cdot m/A$)
   1. 2.51 x 10^-3 T
   2. 1.26 x 10^-3 T
   3. 5.02 x 10^-3 T
   4. 7.54 x 10^-3 T