MCAT Physical : Right Hand Rules
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Example Questions
Example Question #1 : Right Hand Rules
An electron moves at 85km/s to the right along the plane of the page, while a uniform magnetic field points into the page. In what direction does the force act on the moving electron?
Out of the page
Upward along the plane of the page
To the right
Downward along the plane of the page
Into the page at an angle
Upward along the plane of the page
This question requires knowlegde of the right-hand rule. Point the fingers of your right hand in the direction of the electron's velocity (to the right). Point your thumb in the direction of the magnetic field (into the page). Your palm should be facing in the direction of the force on a positive particle. However, electrons are negative, so this direction must be reversed, meaning that the direction of the force is upward along the plane of the page.
Example Question #2 : Right Hand Rules
You look at a circular loop of wire such that the plane of the loop is perpendicular to your line of vision. In what direction must a current be going through the loop in order for a magnetic field to be produced in your direction.
Clockwise and slowly increasing
Counterclockwise
Clockwise but slowly decreasing
The direction of the current does not matter
Clockwise
Counterclockwise
This is an application of the right hand rule for magnetic fields produced by current carrying loops. To use the right hand rule, put your right thumb in the direction of the current, and the direction of the magnetic field is the same as the way your other four fingers wrap as you close your fist. The answers which include increasing or decreasing of a current hint at the concept of induction and are incorrect.
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