How Do Magnetism and Electric Fields Interact in Physics Problems?

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Homework Help Overview

The discussion revolves around the interaction of magnetism and electric fields, with specific reference to problems related to Millikan's oil drop experiment, the motion of an electron towards a proton, the behavior of a proton in a magnetic field, and the induced voltage in a circular coil within a magnetic field.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants explore the implications of electric fields on charged particles, questioning the nature of charge in the context of Millikan's experiment.
  • There is an examination of energy conservation principles in the context of an electron's motion towards a proton, with some confusion about the equations used.
  • Discussion includes the application of the right-hand rule to determine the direction of force on a proton moving in a magnetic field, with participants expressing uncertainty about the correct interpretation.
  • Participants analyze the induced voltage in a coil when flipped in a magnetic field, questioning the methodology used to calculate the change in magnetic flux.

Discussion Status

The discussion is active, with participants sharing their reasoning and calculations while seeking clarification on specific concepts and methodologies. Some guidance has been offered regarding the right-hand rule and the change in magnetic flux, but no consensus has been reached on the interpretations or solutions to the problems presented.

Contextual Notes

Participants express varying levels of confidence in their understanding of physics concepts, indicating a need for foundational clarification on topics such as electric fields, magnetic forces, and energy conservation. There is also mention of potential confusion regarding the application of specific equations and rules.

jekch85
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magnetism and electric fields

Hello all. I'm new to this, but I would really appreciate any help, I'm absolutely terrible at physics...

1) In a trial of Millikan's oil drop experiment, we find that the electric field required to suspend a tiny oil particle with mass 1.46x10^-14 kg is 2.98x10^5 N/C upward. We can infer that the oil particle

a) is missing three electrons
b) is missing two electrons
c) has three extra electrons
d) has two extra electrons

I worked through this problem to the best of my ability and figured that q=4.8x10^-19 when it should equal 1.6x10^-14. So that means there are either three extra or three missing, but I can't seem to figure out which one. I thought three extra, but I could be wrong. Any hints?

3) An electrons 'falls' toward a proton from far away. If it started with zero velocity, how fast is it moving when it gets to a typical atomic distance of 1.0x10^-10 m from the proton?

a) 3.2x10^6 m/s
b) 2.2x10^6 m/s
c) 1.6x10^6 m/s
d) 1.1x10^6 m/s

I used the conservation of energy, PE=KE, which gave me m*a*d/q=.5m*v^2. For some reason I got 1.1x10^5, which is close to d but I have a feeling I did something wrong.

3) The Earth's magnetic field above the Earth's equator is about 10^-4 T northward. If a proton is initially moving upward at 5x10^5 m/s, it will

a) curve east, making a circle with r=50m
b) curve west, making a circle with r=50m
c) curve east, making a circle with r=3 cm
d) curve west, making a circle with r=3 cm
e) keep moving in a straight path

For this question, I got answer a using the equation r=mv/qB. I'm pretty sure that part is right, but what I don't know is which way it will move. I think I'm confusing myself with the right hand rule. Any suggestions would be awesome.

4) I have a 500-turn circular coil of wire, 0.10 m in diameter, in a 0.025 T magnetic field. Initially the plane of the coil is perpendicular to B. If I flip the coil 180 degrees in 1/30 of a second, what is the average voltage created across the ends of the coil?

a) -6.0V
b) -12V
c) -3.0V
d)-24V

I got c for this one. I used found the flux to be 1.96x10^-4 and then I found V by using V=-N(flux)/time. I got -2.94, but is this the right way to solve this type of problem?

Thank you to anyone who can help me!
 
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jekch85 said:
Hello all. I'm new to this, but I would really appreciate any help, I'm absolutely terrible at physics...

1) In a trial of Millikan's oil drop experiment, we find that the electric field required to suspend a tiny oil particle with mass 1.46x10^-14 kg is 2.98x10^5 N/C upward. We can infer that the oil particle

a) is missing three electrons
b) is missing two electrons
c) has three extra electrons
d) has two extra electrons

I worked through this problem to the best of my ability and figured that q=4.8x10^-19 when it should equal 1.6x10^-14. So that means there are either three extra or three missing, but I can't seem to figure out which one. I thought three extra, but I could be wrong. Any hints?
The electric field is upward. Gravity acts downward. Which way does the electric force have to be?
 
jekch85 said:
3) An electrons 'falls' toward a proton from far away. If it started with zero velocity, how fast is it moving when it gets to a typical atomic distance of 1.0x10^-10 m from the proton?

a) 3.2x10^6 m/s
b) 2.2x10^6 m/s
c) 1.6x10^6 m/s
d) 1.1x10^6 m/s

I used the conservation of energy, PE=KE, which gave me m*a*d/q=.5m*v^2. For some reason I got 1.1x10^5, which is close to d but I have a feeling I did something wrong.
Conservation of energy is the correct approach, but I do not recognize m*a*d/q. What is the electrical potential energy of two charges sparated by a distance r?
 
jekch85 said:
3) The Earth's magnetic field above the Earth's equator is about 10^-4 T northward. If a proton is initially moving upward at 5x10^5 m/s, it will

a) curve east, making a circle with r=50m
b) curve west, making a circle with r=50m
c) curve east, making a circle with r=3 cm
d) curve west, making a circle with r=3 cm
e) keep moving in a straight path

For this question, I got answer a using the equation r=mv/qB. I'm pretty sure that part is right, but what I don't know is which way it will move. I think I'm confusing myself with the right hand rule. Any suggestions would be awesome.
There are various right hand rules. The one I prefer is:
fingers of the right hand start in the direction of v and curl through the smalles angle to the direction of B; thumb points in the direction of the force.
 
jekch85 said:
4) I have a 500-turn circular coil of wire, 0.10 m in diameter, in a 0.025 T magnetic field. Initially the plane of the coil is perpendicular to B. If I flip the coil 180 degrees in 1/30 of a second, what is the average voltage created across the ends of the coil?

a) -6.0V
b) -12V
c) -3.0V
d)-24V

I got c for this one. I used found the flux to be 1.96x10^-4 and then I found V by using V=-N(flux)/time. I got -2.94, but is this the right way to solve this type of problem?

Thank you to anyone who can help me!
You started with the flux through the loop in one direction and ended wtih it in the opposite direction, so what was the change?
 

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