How Does a Charged Speck of Dust Behave in Electric and Gravitational Fields?

[AsksQuestions]

Homework Statement

Near to the Earth's surface, a speck of dust with a charge equal to an electron experiences a uniform downward electric field of strength 100NC^-1 and a uniform gravitational field of strength 9.8Nkg^-1.

a)draw a diagram showing the electric field pattern and the sign of the charge on the surface.
b)draw a free-body force diagram for the speck of dust labelling the forces.

Homework Equations

Don't think I need any for the question.

The Attempt at a Solution

a)I don't know where the other charge is. There is one charge on the speck of dust, but where does the field act?
b)I know the gravitation field will act downwards. And I think the electric field always acts in the opposite direction to the gravitation field? So it will act upwards? But then it has a negative charge (equal to electron) so that confuses me.

 

[quantumdude]

Homework Equations

Don't think I need any for the question.

Right you are.

The Attempt at a Solution

a)I don't know where the other charge is. There is one charge on the speck of dust, but where does the field act?

The other charge is distributed over the surface of the Earth. And the speck of dust is suspended in a uniform electric field. That means the field acts everywhere for the purposes of this problem.

b)I know the gravitation field will act downwards. And I think the electric field always acts in the opposite direction to the gravitation field? So it will act upwards? But then it has a negative charge (equal to electron) so that confuses me.

There is no correlation between the direction of the gravitational and electric fields. The correlation is determined by the direction of the electric field and the charge of the particle suspended in the field.