# Help with with finding the magnitude of a charge

• dasblack
In summary, the weight of a 1.0 kg object of charge Q is balanced by an object of equal but opposite charge fixed to a support 74 cm above it. The magnitude of the charge Q is calculated using the equations F=ke|q1||q2| / r^2 and F=ma, resulting in the answer of 24.4 μC.
dasblack

## Homework Statement

The weight of a 1.0 kg object of charge Q is just balanced by another object of equal but opposite charge fixed to a support 74 cm above it. What is the magnitude of the charge Q (in μC)?

## Homework Equations

F=ke|q1||q2| / r^2
F=ma

## The Attempt at a Solution

F=(1kg)(9.8m/s^2) = 9.8

9.8=8.99e9(q^2) / .74^2 = 24.4 uC
I think that's the right way, I'm not too sure.

Thanks

Last edited:
dasblack said:

## Homework Statement

The weight of a 1.0 kg object of charge Q is just balanced by another object of equal but opposite charge fixed to a support 74 cm above it. What is the magnitude of the charge Q (in μC)?

## Homework Equations

F=ke|q1||q2| / r^2
F=ma

## The Attempt at a Solution

F=(1kg)(9.8m/s^2) = 9.8

9.8=8.99e9(q^2) / .74^2 = 24.4 uC

Hmmm...

Yes equating the attrative force of electromagnetism to it's weight is the right way to go about the problem

0 = (kQq / r2) - mg

mg = (kQ2 / r2)

mgr2 = (kQ2

mgr / k = Q2

sqrt{ (mgr / k) } = Q

If that is what you've done then good on you! Numerically my answer comes out at: 2.84*10-5 C

In μC , 24μC I think...

Hope this helps!
Haths

Haths said:
Hmmm...

Yes equating the attrative force of electromagnetism to it's weight is the right way to go about the problem

0 = (kQq / r2) - mg

mg = (kQ2 / r2)

mgr2 = (kQ2

mgr / k = Q2

sqrt{ (mgr / k) } = Q

If that is what you've done then good on you! Numerically my answer comes out at: 2.84*10-5 C

In μC , 24μC I think...

Hope this helps!
Haths

Yes, 24.4 is the answer, thank you for the help.

## 1. What is the equation for finding the magnitude of a charge?

The equation for finding the magnitude of a charge is Q = ne, where Q is the charge in coulombs, n is the number of charged particles, and e is the elementary charge.

## 2. How do I determine the number of charged particles in a system?

The number of charged particles in a system can be determined by counting the number of protons or electrons in the system. Alternatively, it can also be calculated using the Avogadro's number (6.022 x 10^23) and the molar mass of the substance.

## 3. Can the magnitude of a charge be negative?

Yes, the magnitude of a charge can be negative. This means that the charge is a negative multiple of the elementary charge and indicates the presence of excess electrons in the system.

## 4. How does the distance between two charged objects affect the magnitude of their charges?

The magnitude of the charges on two objects is inversely proportional to the square of the distance between them. This means that as the distance between two charged objects decreases, the magnitude of their charges increases.

## 5. What units are used to measure the magnitude of a charge?

The magnitude of a charge is measured in coulombs (C), which is the standard unit of electric charge in the International System of Units (SI).

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