# How to determine the magnitude of the electric force

• hotram
In summary,A piece of tape is pulled from a spool and lowered toward a 170-mg scrap of paper. Only when the tape comes within 8.0 mm is the electric force magnitude great enough to overcome the gravitational force exerted by Earth on the scrap and lift it.The force is attractive, directed upward.
hotram

## Homework Statement

A piece of tape is pulled from a spool and lowered toward a 170-mg scrap of paper. Only when the tape comes within 8.0 mm is the electric force magnitude great enough to overcome the gravitational force exerted by Earth on the scrap and lift it.

Determine the magnitude and direction of the electric force exerted by the tape on the paper at this distance

## Homework Equations

Coulomb's Law:
Force (electric)= k(Q1*Q2)/(r^2)

## The Attempt at a Solution

[/B]
I was not sure how to approach this problem.
But I converted 170mg=.17g and 8mm=.008m

The force is attractive, directed upward

Since k is 9*10^(9) N*(m^2)/(C^2)
and we know that the distance between the tape and the paper is .008m
I assume that we need to find the charges of the tape and the paper.

I know an electron charge is -1.602*10^(19) C

I thought that needed to see how many electrons there are in the .17g of tape. But I do not know the chemical makeup of the tape or the paper. So I don't know how many electrons there are. In other words, I am not sure how to find the charges Q1 and Q2

Welcome to PF!

Suppose a calculator of mass 100 g rests on a table top. How much force would be required to lift the calculator off the table?

100g= .1kg
(.1kg)(9.8m/s^2)= .98N?

TSny said:
Welcome to PF!

Suppose a calculator of mass 100 g rests on a table top. How much force would be required to lift the calculator off the table?
.98N
100g=.1kg
.1kg*9.8m/s^2=.98N

hotram said:
100g= .1kg
(.1kg)(9.8m/s^2)= .98N?
Yes. Can you apply the same idea to your question about the electrical force of the tape?

TSny said:
Yes. Can you apply the same idea to your question about the electrical force of the tape?
I am not quite sure. The calculator scenario is F=ma.
The tape and paper scenario is an electrical scenario.
I am just not quite sure where the example is getting at.
I know that F(mag. of E.field)= q*E
But I am unsure of how to put these pieces together

hotram said:
The tape and paper scenario is an electrical scenario.
The calculator had a mass of 100gm.
The paper has a mass of 170mg. How much force is required to pull the paper up? Which force is pulling the paper up?

hotram said:
I am not quite sure. The calculator scenario is F=ma.
The tape and paper scenario is an electrical scenario.
I am just not quite sure where the example is getting at

Note that TSny asked you to calculate the magnitude of the force required to lift the calculator. He didn't specify what the source of that force was. Does the source of the force (eg crane, hand, rocket, magnetic, electrostatic) make a difference to the magnitude and direction?

TSny said:
Yes. Can you apply the same idea to your question about the electrical force of the tape?
Thank you
F(elec.)=.001666

hotram said:
Thank you
F(elec.)=.001666
Good. All you need to do is add the units and the direction of the force.

hotram
TSny said:
Good. All you need to do is add the units and the direction of the force.
[/Q
Would the units be Newtons or Coulombs ?

Cruise Ten said:
Would the units be Newtons or Coulombs ?
Which of these corresponds to a unit for force?

TSny said:
Which of these corresponds to a unit for force?
haha, thanks!

## 1. How do you calculate the magnitude of the electric force between two charged particles?

The magnitude of the electric force between two charged particles can be calculated using Coulomb's law. This law states that the force is directly proportional to the product of the two charges and inversely proportional to the square of the distance between them. The formula for calculating the magnitude of the electric force is F = k * (q1 * q2)/r^2, where k is the Coulomb's constant, q1 and q2 are the charges of the two particles, and r is the distance between them.

## 2. What is the unit of measurement for electric force?

The unit of measurement for electric force is Newtons (N). This is the same unit used to measure other types of forces such as gravity and friction. This unit is named after Sir Isaac Newton, who first described the laws of motion.

## 3. How does the magnitude of the electric force change with distance?

The magnitude of the electric force follows an inverse square relationship with distance. This means that as the distance between two charged particles increases, the force between them decreases. For example, if the distance between two particles is doubled, the force between them will decrease by a factor of four.

## 4. Does the magnitude of the electric force depend on the type of charge?

Yes, the magnitude of the electric force depends on the type of charge. Like charges (positive and positive, or negative and negative) will repel each other, while opposite charges (positive and negative) will attract each other. This means that the force between two particles with the same type of charge will be repulsive, while the force between two particles with different types of charge will be attractive.

## 5. Can the magnitude of the electric force be negative?

Yes, the magnitude of the electric force can be negative. This can happen when the two charged particles have opposite types of charge. In this case, the force will be attractive, but the negative sign indicates that the force is acting in the opposite direction of the positive charge. However, it is important to note that the magnitude of the electric force is always positive, as it represents the strength of the force.

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