# Finding the E-field of a mass hanging from a string

• aximwolf
In summary, the conversation discusses a problem in which a ball with a known mass and positive charge is suspended in a uniform electric field. The ball hangs at a certain angle, and the conversation focuses on finding the magnitude of the electric field. The conversation includes calculations using the equations Fx=Fe-Tsin(theta)=0 and Fy=Tcos(theta)=0, which lead to the final result of E=Fe/q=Tan(theta)mg. It is noted that the mass should have been specified in a particular unit and that the problem should have been posted in a homework forum.
aximwolf
9. [1pt]

As shown in the figure above, a ball of mass 0.480 g and positive charge q =32.7microC is suspended on a string of negligible mass in a uniform electric field. We observe that the ball hangs at an angle of theta=15.0o from the vertical. What is the magnitude of the electric field?

Fx= Fe - Tsin(theta)= 0
Fy= Tcos(theta) = 0

Tsin(theta)/Tcos(theta) = Fe\mg

Than E= Fe/q

So Tan(theta)mg = Fe/q = E

I got (Tan(15)*.480*9.8)/32.7e-6= 3.9 e 4
Where did I go wrong?

Note the units in which the mass was specified.

EDIT: Note also that since this is a homework problem, it should have been posted in one of the homework forums, in particular the Introductory Physics Forum.

EDIT by mentor: this thread has been moved to the appropriate location.

Last edited by a moderator:
Its right! Thank you for responding so fast!

## 1. How do you find the E-field of a mass hanging from a string?

The E-field can be found by using the equation E = kq/r^2, where k is the Coulomb constant, q is the charge of the mass, and r is the distance from the mass to the point where the E-field is being measured.

## 2. What is the significance of finding the E-field of a mass hanging from a string?

Finding the E-field can help us understand the electric field strength and direction at a certain point due to the presence of the charged mass. This information can be important in understanding how charged particles interact with each other.

## 3. Can the E-field change if the mass is moved to a different location?

Yes, the E-field will change if the distance between the mass and the point where the E-field is being measured changes, as the distance is a factor in the calculation of the E-field.

## 4. How does the charge of the mass affect the E-field?

The charge of the mass directly affects the E-field, as seen in the equation E = kq/r^2. A higher charge will result in a stronger E-field, while a lower charge will result in a weaker E-field.

## 5. Can the E-field be negative?

Yes, the E-field can be negative. The negative sign indicates the direction of the field, not its strength. A negative E-field means that the direction of the field is opposite to the direction of the positive charge.

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