MCAT Physical : Right Hand Rules

Study concepts, example questions & explanations for MCAT Physical

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Example Questions

Example Question #2 : Magnetism And Electromagnetism

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?

Possible Answers:

Upward along the plane of the page

Downward along the plane of the page

To the right

Into the page at an angle

Out of the page

Correct answer:

Upward along the plane of the page

Explanation:

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 #3 : Magnetism And Electromagnetism

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.

Possible Answers:

Clockwise

Counterclockwise

Clockwise and slowly increasing

The direction of the current does not matter

Clockwise but slowly decreasing

Correct answer:

Counterclockwise

Explanation:

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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