Finding the charge on two beads?

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In summary, two small insulating spherical beads are placed on a taut(insulating, isolated) string which has a knot at its lower end. The beads are given identical positive charges and can move frictionlessly on the string. One bead rests against the knot while the other comes to rest 5cm away. The mass of each bead is 0.1g. In order for the bead to remain at rest, there must be a normal force between the bead and the string and the net forces must be 0. The charge on the beads can be calculated using the equation Fnet=ma=0.
  • #1
janetxo
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Homework Statement


Two small insulating spherical bead are placed on a taut(insulating, isolated) string which has a knot at its lower end. The string is stretched at an angle of 60degress to the horizontal. The beads can move frictionlessly on the string. The beads are given identical positive charges (which are distributed evenly over the tiny volumes of the beads). The lower bead rests against the knot. The other bead comes to rest 5cm away from the knot on the string. The mass of each bead is 0.1g. What is the charge on the beads?

Homework Equations




The Attempt at a Solution


Would I use work? Or something else? Not quite sure
Just an idea of even what equation to start with would be nice
 
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  • #2
Think about how it is possible that the bead can remain at rest. What forces act on the bead?
 
  • #3
well there would be the force that pushes the two beads apart, and gravity?
 
  • #4
TSny said:
Think about how it is possible that the bead can remain at rest. What forces act on the bead?

Well there would be the force that pushed the two beads away, and gravity?
 
  • #5
janetxo said:
Well there would be the force that pushed the two beads away, and gravity?

Yes. But there is a third force. Hint: The bead is in contact with the string.

What is the condition that must be met by these 3 forces for the bead to remain at rest?
 
  • #6
TSny said:
Yes. But there is a third force. Hint: The bead is in contact with the string.

What is the condition that must be met by these 3 forces for the bead to remain at rest?

So, a normal force between the bed and the string? (as there is no friction). and the net forces would have to be 0 in order for it to be at rest. Fnet=ma=0.
 
  • #7
janetxo said:
So, a normal force between the bed and the string? (as there is no friction). and the net forces would have to be 0 in order for it to be at rest. Fnet=ma=0.
Yes, that's right.
 
  • #8
TSny said:
Yes, that's right.

thanks for walking me through that bit! Wasnt quite sure how to start, :) really apperiate it
 
  • #9
Good work. Welcome to PF!
 

1. How do you determine the charge on two beads?

To determine the charge on two beads, you need to measure the force between them using a calibrated instrument such as an electroscope or a Coulomb balance. The force between the two beads can then be used to calculate the charge using Coulomb's Law.

2. Can the charge on two beads be different?

Yes, the charge on two beads can be different. This can happen if the beads are made of different materials, have been rubbed against different materials, or if they have different sizes or shapes. The charge on each bead will depend on the amount of electrons transferred or redistributed during the rubbing process.

3. What factors affect the charge on two beads?

The charge on two beads can be affected by various factors such as the materials of the beads, the rubbing process, the environmental conditions (e.g. humidity), and the distance between the beads. These factors can influence the transfer or redistribution of electrons and therefore affect the final charge on the beads.

4. Can two beads have the same charge?

Yes, two beads can have the same charge. This can happen if both beads are made of the same material and have been rubbed against the same material, or if they have been exposed to the same environmental conditions. In this case, the amount of charge on each bead will be equal.

5. What if the charge on two beads is too small to measure?

If the charge on two beads is too small to measure directly using an instrument, it can still be calculated using Coulomb's Law. However, in this case, the measurements and calculations may have a higher margin of error. It is important to use a sensitive instrument and carefully control the experimental conditions to obtain accurate results.

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