# Exploring Magnetism & Electric Fields

• jekch85
In summary, magnetism and electric fields were discussed in the conversation. The first question involved finding the missing or extra electrons on a tiny oil particle based on the electric field required to suspend it. The second question involved calculating the speed of an electron as it falls towards a proton from a far distance. The third question discussed the direction in which a proton would move when initially moving upward in the Earth's magnetic field. The fourth question involved finding the average voltage created across the ends of a coil when it is flipped in a magnetic field. Various equations and approaches were used to solve the problems, including the conservation of energy and the right hand rule.
jekch85
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!

Last edited:
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?

## 1. What is the difference between magnetism and electricity?

Magnetism and electricity are both forms of electromagnetism, but they have some key differences. Magnetism is a force that attracts or repels certain materials, such as iron or cobalt. It is caused by the movement of charged particles, such as electrons, in a substance. Electricity, on the other hand, is the flow of electric charge through a conductor. It can be generated by moving a magnet through a coil of wire or by chemical reactions.

## 2. How are magnetic fields created?

Magnetic fields are created by moving electric charges. In atoms, electrons orbit around the nucleus, creating a tiny magnetic field. When many atoms are aligned in the same direction, their magnetic fields add up to create a larger magnetic field. This is how magnets are formed. In addition, electric currents also create magnetic fields. This is why a wire carrying electricity can become magnetized.

## 3. Can electric fields exist without magnetic fields and vice versa?

Yes, electric and magnetic fields are often found together, but they can exist separately. A changing magnetic field can create an electric field, and a changing electric field can create a magnetic field. However, it is possible to have a stationary electric field without a magnetic field and vice versa.

## 4. How do magnetic fields affect charged particles?

Magnetic fields affect charged particles by exerting a force on them. The direction of the force depends on the direction of the magnetic field and the velocity of the charged particle. In a magnetic field, charged particles will experience a force perpendicular to both the direction of the magnetic field and the direction of their motion. This is why charged particles, such as electrons, will move in a circular path when they enter a magnetic field.

## 5. What are some real-life applications of magnetism and electric fields?

Magnetism and electric fields have many practical applications in our daily lives. Some examples include electric motors, which use a combination of electric and magnetic fields to convert electrical energy into mechanical energy, and generators, which do the opposite. Magnetic resonance imaging (MRI) machines also use magnetic fields to produce detailed images of the inside of the body. Electric fields are used in electronic devices, such as computers and smartphones, to transfer and store information. Additionally, magnets are used in many industries, such as transportation and energy production, to improve efficiency and performance.

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