Q: Two charges, each $$Q = 4.7\ \mu\mathrm{C}$$, are placed $$10.0\ \mathrm{cm}$$ apart. What is the magnitude of the electric field at the midpoint between them?

$$1.70 \times 10^6$\ \mathrm{N/C}$$

Question 1

Three positive particles, each with charge $$q = 17.0\ \mu\mathrm{C}$$, are placed at the corners of an equilateral triangle with sides of $$15.0\ \mathrm{cm}. $$What is the magnitude of the net force on one particle due to the other two? (Use $$k = 8.99 	imes 10^9$\ \mathrm{N\cdot m^2$/C^2$$}$)

Accepted Answer

$$28.7\ \mathrm{N}$$

Question 2

What is the direction of the net force on each charge in the equilateral triangle configuration described above?

Accepted Answer

Perpendicular to the side opposite the charge, away from the triangle

Question 3

If the side length of the triangle is doubled, how does the magnitude of the net force on each charge change?

Accepted Answer

It is quartered

Question 4

Which equation correctly expresses the magnitude of the force between two point charges $$q_1$$ and $$q_2$$ separated by distance $$r$$?

Accepted Answer

$$F = k \dfrac{q_1$ q_2$}{r^2$}$$

Question 5

Two charges, each $$Q = 4.7\ \mu\mathrm{C}$$, are placed $$10.0\ \mathrm{cm}$$ apart. What is the magnitude of the electric field at the midpoint between them?

Accepted Answer

$$1.70 	imes 10^6$\ \mathrm{N/C}$$

Question 6

At point A (directly above the midpoint between two equal positive charges), what is the direction of the net electric field?

Accepted Answer

Upward and away from the midpoint, along the perpendicular bisector

Question 7

Which of the following best describes the superposition principle as applied to electric fields?

Accepted Answer

The net electric field at a point is the vector sum of the electric fields produced by each charge

Question 8

If one of the charges in the triangle is replaced with a negative charge of the same magnitude, what happens to the net force on the other two charges?

Accepted Answer

The net force increases and points toward the negative charge

Question 9

A charge $$q is $$placed at the center of the triangle formed by three equal charges at the corners. What is the net force on the central charge?

Accepted Answer

Zero

Question 10

Which of the following is the correct expression for the electric field $$E$$ due to a point charge $$Q at a $$distance $$r$$?

Accepted Answer

$$E = k \dfrac{Q}{r^2$}$$

Question 11

If the distance between two charges is tripled, how does the force between them change?

Accepted Answer

It becomes one-ninth as large

Question 12

Which of the following statements about electric field lines is correct?

Accepted Answer

They start on positive charges and end on negative charges

Question 13

A student calculates the force between two charges and gets a negative value. What does this indicate?

Accepted Answer

The force is attractive

Question 14

If the charges in the triangle are doubled, what happens to the net force on each charge?

Accepted Answer

It increases by a factor of 4

Question 15

Which of the following is a correct application of Coulomb's law in vector form?

Accepted Answer

$$\vec{F} = k \dfrac{q_1$ q_2$}{r^2$} \hat{r}$$

Electrostatics: Forces and Electric Fields (Coulomb's Law)

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