Textbook Question
An electron is projected vertically upward with a speed of 1.70 x 106 m/s into a uniform magnetic field of 0.550 T that is directed horizontally away from the observer. Describe the electron’s path in this field.
684
views
28. Magnetic Fields and Forces
Force on Moving Charges & Right Hand Rule
Multiple Choice
Which description best matches the use of the right-hand palm rule for determining the direction of force on a positive charge moving in a magnetic field? (force), (positive charge), (magnetic field), and (velocity) are involved.
A
Point your fingers in the direction of the magnetic field , your thumb in the direction of the velocity of the positive charge , and your palm will face the direction of the force .
B
Point your thumb in the direction of the magnetic field , your fingers in the direction of the force , and your palm in the direction of the velocity .
C
Point your fingers in the direction of the velocity of the positive charge , align your palm so it faces the direction of the magnetic field , and your thumb will point in the direction of the force .
D
Point your thumb in the direction of the force , your fingers in the direction of the velocity , and your palm in the direction of the magnetic field .
Verified step by step guidance1
Recall that the magnetic force \( \vec{F} \) on a positive charge \( q \) moving with velocity \( \vec{v} \) in a magnetic field \( \vec{B} \) is given by the Lorentz force equation:
\[ \\vec{F} = q \\vec{v} \\times \\vec{B} \]
Understand that the direction of the force \( \vec{F} \) is given by the right-hand rule for the cross product \( \\vec{v} \\times \\vec{B} \). This means the force is perpendicular to both velocity and magnetic field vectors.
To apply the right-hand palm rule correctly: point your fingers in the direction of the velocity \( \vec{v} \) of the positive charge, then curl your fingers toward the magnetic field \( \vec{B} \). Your thumb will then point in the direction of the force \( \vec{F} \).
Note that the problem's correct description uses a slightly different but equivalent convention: point your fingers in the direction of the magnetic field \( \vec{B} \), your thumb in the direction of the velocity \( \vec{v} \), and your palm will face the direction of the force \( \vec{F} \). This is a common variant of the right-hand rule.
Remember this mnemonic: Fingers \( \rightarrow \) magnetic field \( \vec{B} \), Thumb \( \rightarrow \) velocity \( \vec{v} \), Palm \( \rightarrow \) force \( \vec{F} \) on a positive charge. This helps determine the force direction without ambiguity.
Related Videos
Related Practice
