What is the Force Exerted on a Ball Dropped into a Horizontal Magnetic Field?

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In summary, the conversation discusses two physics problems involving magnetic fields and particles in motion. The first problem involves a particle moving south in a vertically downward magnetic field and being deflected toward the east. The group eventually determines that the particle must have a positive charge to be deflected in that direction. The second problem involves a ball containing excess electrons being dropped into a vertical shaft and then entering a horizontal magnetic field. The group discusses the formula for electromagnetic force and determines that the only missing piece of information needed to find the force is the velocity of the ball. They suggest using the length of the shaft, acceleration, and initial velocity to find the velocity at the moment the ball enters the magnetic field.
  • #1
kristi.lynn
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Hey I tried posting this in another thread but no one was answering and I'm really quite stuck...

ok here's my problem(s)... I think the first one I'm missing something...

it says:

A particle initially moving south in a vertically downward magnetic field is deflected toward the east. What is the sign of the charge on the particle? Explain your answer with a diagram.

So the way I drew it I've got the B-field pointing down and the particle moving in the same direction as the B-field... so if I'm looking at something like the RHR then I figure there's like no force on the particle which makes it not be deflected! I've read the chapter and I figure I MUST be missing something but it's not helping at all... so if anyone can give me some guidance that would be great... ok second question...

A 150-g ball containing 4.00E8 excess electrons is dropped into a 125-m vertical shaft. At the bottom of the shaft, the ball suddenly enters a uniform horizontal magnetic field that has magnitude 0.250 T and direction from east to west. If air resistance is negligibly small, find the magnitude and direction of the force that this magnetic field exerts on the ball just as it enters the field.

ok now this one I assumed that q= -4.00E8 and my biggest problem is I can't figure out how to find the velocity of the ball. I tried F=mg and got the force due to gravity but that didn't tell me the velocity of the ball and I don't know if it CAN exactly... I was going to first use F=qv X B but then I figured maybe F=Il X B would be better bc they gave me the length too but I just don't know where to go! Please help me! :cry:

kristi.lynn
 
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  • #2
ok I think I might have gotten the first one... I just figured if it's got to be deflected east then there must be some force to the east so by the equation F=qv X B for F to be in the +x direction or East, and with v being in the - y direction and B also in the -y direction, then + = q (-)(-) and so q must be positive... that's the best I could figure...
 
  • #3
In the second question, the first thing you need to know is the formula for electromagnetic force(which you already do: F=qv x B.

So, to find the force, you need to know the charge, the velocity and the strength of the B-field. The strength of the B-field is given: 0.250 T. Then you need to know the charge, which is also given: 4.00E8 multiplied by the charge of a electron. What is left is the velocity. You know the length of the shaft, the acceleration(what forces act on it while it is in free fall?) and the initial velocity(...electrons is dropped into a 125m...). Can you find the velocity of the ball the moment it enters the magnetic field?

If you work all that out, you'll realize that the question is pretty straight forward.
 

1. What is magnetism?

Magnetism is a fundamental force in the universe that causes objects to attract or repel each other. It is a result of the movement of charged particles, such as electrons, within atoms.

2. How do magnets work?

Magnets have two poles, north and south, that interact with each other. Like poles repel each other, while opposite poles attract. This is because the magnet's magnetic field lines flow from the north pole to the south pole.

3. What is a magnetic field?

A magnetic field is an invisible area of influence around a magnet. It is created by the movement of charged particles and is strongest near the magnet's poles. Other magnets or magnetic materials can be affected by this field.

4. How are magnetic fields used?

Magnetic fields have many practical applications, such as in compasses for navigation, electric motors and generators, MRI machines for medical imaging, and speakers and headphones for sound production. They are also used in data storage devices, such as hard drives and credit cards.

5. Can magnetic fields be shielded?

Yes, magnetic fields can be shielded by using materials that are not affected by them, such as iron, steel, or certain alloys. These materials redirect the magnetic field lines, preventing them from reaching the desired area. This is commonly used in electronic devices to prevent interference from external magnetic fields.

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