Direction of magnetic field

[663697]

The researchers use a negatively charged cryogen in the experiment. A negative charge is located at the center of the lesion. The charge's velocity should be in which direction so that the magnetic force on it reinforces the force from the electric field?

A. Up (correct)
B. Down.

I had trouble figuring out which direction the magnetic field was pointing in which is needed to solve the problem. The explanation says since the cryogen is moving rightward, it generates a magnetic field pointing into the page. How do we come to that conclusion? Seems like I forgot quite a bit of magnetism..

For context:

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[Doogie.Howser]

To find the direction of the magnetic field, review your right-hand rules. There are two of them, but the one to figure out which way the magnetic field is pointing surrounding a wire with current is the easier one to remember. With your right hand, do a 'thumbs-up' sign with your thumb pointing in the direction of the current in the wire on the circulating cryogen. The way your fingers naturally curl is the direction of the magnetic field. So using this method, your thumb points to the right and your fingers curl up to show the magnetic field is coming up and out of the page at the site of the targeted tissue.

Hope this helps! And you should google pictures of the right-hand rule for a refresher

 

[663697]

To find the direction of the magnetic field, review your right-hand rules. There are two of them, but the one to figure out which way the magnetic field is pointing surrounding a wire with current is the easier one to remember. With your right hand, do a 'thumbs-up' sign with your thumb pointing in the direction of the current in the wire on the circulating cryogen. The way your fingers naturally curl is the direction of the magnetic field. So using this method, your thumb points to the right and your fingers curl up to show the magnetic field is coming up and out of the page at the site of the targeted tissue.

Hope this helps! And you should google pictures of the right-hand rule for a refresher

Not 100% sure but shouldn't it be the left hand instead since it's a negative charge?

Edit: It's asking to find the velocity such that the force will be in the rightward direction. Do we point the palm of our hand in the rightward direction to figure it out?

 

[Doogie.Howser]

Use whichever method is best for you to understand. But beware, if you need to find the force acting on the object that happens to have a negative charge, yes you're correct that it opposite of the right-hand rule. But that does not mean that miraculously the presence of a negative charge flipped the magnetic fields surrounding it, no. The magnetic field is still the same direction, thus use the right-hand rule. But to find the force, the force changes 180 degrees for the negative charge, yes.
Make sense?

 

[663697]

Use whichever method is best for you to understand. But beware, if you need to find the force acting on the object that happens to have a negative charge, yes you're correct that it opposite of the right-hand rule. But that does not mean that miraculously the presence of a negative charge flipped the magnetic fields surrounding it, no. The magnetic field is still the same direction, thus use the right-hand rule. But to find the force, the force changes 180 degrees for the negative charge, yes.
Make sense?

Yes, but looking back at the question don't you need to know the direction of the external magnetic field (into/out of the page) in order to figure out which direction the velocity should be? The magnetic field we were discussing above is that which the wire itself produces right?

 

[663697]

bump