Posted by Mary on Monday, November 5, 2007 at 8:19pm.

A charged particle, passing through a certain region of space, has a velocity whose magnitude and direction remain constant.

(a) If it is known that the external magnetic field is zero everywhere in this region, can you conclude that the external electric field is also zero?

Explain.

(b) If it is known that the external electric field is zero everywhere, can you conclude that the external magnetic field is also zero?

Explain.


For Further Reading

Physics - bobpursley, Monday, November 5, 2007 at 9:07pm
I will be happy to critique your thinking. It is not nice to post a lot of questions with each a different name. Usually, slackers or answer moochers do that.



Physics - Mary, Monday, November 5, 2007 at 9:29pm
I am sorry but you are mistaken. This is the first time I have been on this website in about 3 weeks. I have posted the question just above this one as well and another one just a minute ago for you to check my working. I will make an educated guess and repost the question.

My educated guess:

a. Yes. The particle has zero acceleration because magnitude and direction of the velocity are constant. If a charged particle passes through an electric field some force will be exerted on it. However, the magnetic field is zero therefore the magnetic force is zero. Net force = electric force. So, if the net foce is zero, then the electric field must therefore be zero.

b. No. If the paricle moves parallel to the magnetic field then no force will act on it.

Both of your answers are correct. Good thinking on (b), especially. I had forgotten about the parallel B field situation, where there is no force.

Correct.

(a) To determine whether the external electric field is zero in the given scenario where the charged particle has a constant velocity and the magnetic field is zero, we can use the fact that the net force on the particle is zero.

When a charged particle moves through an electric field, it experiences a force due to the electric field. This force can change the direction or magnitude of the particle's velocity, resulting in acceleration. However, in this case, we are told that the particle's velocity remains constant, which implies zero acceleration.

Since the net force on the particle is zero, it means that the electric force acting on the particle must be balanced by another force. In the absence of a magnetic field, the only possibility is that the external electric field is also zero.

Therefore, we can conclude that if the velocity of a charged particle remains constant while passing through a region with a zero external magnetic field, the external electric field in that region must also be zero.

(b) In the given scenario where the external electric field is known to be zero everywhere, we need to determine if the external magnetic field is also zero.

When a charged particle moves through a magnetic field, it experiences a magnetic force. This force can change the direction or magnitude of the particle's velocity, resulting in acceleration. However, if the external electric field is zero, the net force on the particle should also be zero.

If the particle moves parallel to the magnetic field, then the magnetic force acting on the particle would be zero. However, if the particle moves perpendicular to the magnetic field, it will experience a magnetic force that may change its velocity.

Therefore, we cannot conclusively determine whether the external magnetic field is zero based solely on the information that the external electric field is zero everywhere. The particle's behavior, such as its path and any changes in velocity, would need to be analyzed further to make a determination about the external magnetic field.

In summary, if the external electric field is zero, we cannot conclude that the external magnetic field is also zero.