High School Physics : Understanding the Right Hand Rules

Study concepts, example questions & explanations for High School Physics

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Example Questions

Example Question #1 : Understanding The Right Hand Rules

A current runs through a wire such that it generates a magnetic field. The magnetic field is in the clockwise direction in the plane of your computer screen. What is the direction of the current?

Possible Answers:

More information is needed to solve

Out of the screen

Into the screen

Counter-clockwise

Clockwise

Correct answer:

Into the screen

Explanation:

To solve this problem use the right hand rule. Take your right hand and make a fist. Now stick your thumb straight up. This will show you the relationship between current and magnetic field: if the magnetic field is your fingers, the current is your thumb.

In this problem, the only way you can get your fingers to be going clockwise in a plane is if your thumb is pointed directly at that plane. Point your thumb directly at the screen. Your fingers will naturally curl in the clockwise direction. The current must be going into the screen.

Example Question #2 : Understanding The Right Hand Rules

A current runs through a straight wire from right to left. What direction would the magnetic field be?

Possible Answers:

Into the screen

Out of the screen

Counter-clockwise

Right to left

Left to right

Correct answer:

Counter-clockwise

Explanation:

For this problem, use the right hand rule. Take your right hand, stick your thumb straight up and curl your fingers around in a "thumbs up" shape.

If your thumb is the current, your fingers will be the magnetic field. With your thumb pointing to the left (the direction of the current), your fingers will curl in a counter-clockwise direction.

Note that the right hand rule for a straight wire is different from the right hand rule for a planar magnetic field!

Example Question #1 : Understanding The Right Hand Rules

A straight wire carries a current directly into your computer screen. In what direction would the magnetic field be?

Possible Answers:

Out of the screen

Right to left

Counter-clockwise

Into the screen

Clockwise

Correct answer:

Clockwise

Explanation:

For this problem, use the right hand rule. Take your right hand, stick your thumb straight up, and curl your fingers around in a "thumbs up" shape.

If your thumb is the current, your fingers will be the magnetic field. With your thumb pointing away from your face, or toward your computer screen (the direction of the current), your fingers will curl in a clockwise direction.

Note that the right hand rule for a straight wire is different from the right hand rule for a planar magnetic field!

Example Question #2 : Understanding The Right Hand Rules

A straight wire carries a current directly out of your computer screen. In what direction would the magnetic field be?

Possible Answers:

Into the screen

Counter-clockwise

Out of the screen

Clockwise

Left to right

Correct answer:

Counter-clockwise

Explanation:

For this problem, use the right hand rule. Take your right hand, stick your thumb straight up, and curl your fingers around in a "thumbs up" shape.

If your thumb is the current, your fingers will be the magnetic field. With your thumb pointing toward your face, or out from your computer screen (the direction of the current), your fingers will curl in a counter-clockwise direction.

Note that the right hand rule for a straight wire is different from the right hand rule for a planar magnetic field!

Example Question #3 : Understanding The Right Hand Rules

A negatively charged particle is moving to the right along a vertical plane. If the force generated by a constant magnetic field is directed upwards within plane, in what direction is the magnetic field?

Possible Answers:

Out of the plane, toward the observer

Downwards within the plane

Out of the plane, away from the observer

Upward within the plane

Correct answer:

Out of the plane, toward the observer

Explanation:

This question requires you to apply the right hand rule. Your thumb will point to the right, in the direction of the particle's velocity. For the negatively charged particle to feel an upward force, the back of your hand, not your palm as would be the case with a positively charged particle needs to be facing up. Extension of your fingers makes the magnetic field point out of the plane, toward you. 

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