Question 1

A charge $$q_1 = -3.0$$ 	imes $$10^{-6}$$\,\mathrm{C}$$ is located at the origin, and a charge q_2$ = 5.0 	imes 10$$^{-6}$$\,\mathrm{C} is $$located at $$(0.040\,\mathrm{m}, 0.030\,\mathrm{m}). $$What is the magnitude of the force exerted on $$q_2 by$$ $$q_1$$? Use $$k = 9.0 	imes 10^9$\,\mathrm{N\cdot m^2$/C^2$$}$.

Accepted Answer

$$84\,\mathrm{N}$$

Question 2

Given three charges: $$q_1 = -3.0$$ 	imes $$10^{-6}$$\,\mathrm{C}$$ at the origin, q_2$ = 5.0 	imes 10$$^{-6}$$\,\mathrm{C} at$$ $$(0.040\,\mathrm{m}, 0.030\,\mathrm{m})$$, and $$q_3 = 3.0$$ 	imes $$10^{-6}$$\,\mathrm{C}$$ at (0$$, 0.030\,\mathrm{m})$$, what is the magnitude of the net force on q_2$ due to q_1$ and q_3$?

Accepted Answer

$$52\,\mathrm{N}$$

Question 3

Which of the following correctly describes the direction of the electric field created by a positive point charge?

Accepted Answer

It points away from the charge.

Question 4

A positively charged particle is placed at $$x = 0.1\,\mathrm{m} on $$the x-axis, with a $$+q$$ charge at the origin. What is the direction of the electric field at $$x = 0.1\,\mathrm{m}$$?

Accepted Answer

In the positive x direction.

Question 5

If a negative charge is placed in an electric field $$\vec{E}$$, what is the direction of the force $$\vec{F} on $$the charge?

Accepted Answer

Opposite to the direction of $$\vec{E}.$$

Question 6

The electric field at a point due to a point charge $$q is $$given by which of the following equations?

Accepted Answer

$$\vec{E} = \frac{1}{4\pi\$$varepsilon_0$$} \frac{q}{r^2$} \hat{r}$$

Question 7

Which statement is true about the electric field created by a point charge as you move farther away from the charge?

Accepted Answer

The electric field decreases in magnitude.

Question 8

Two charges, $$+4Q$$ and $$-Q$$, are placed on a line. At which location is it possible for the electric field to be zero?

Accepted Answer

On the side of $$+4Q$$ away from $$-Q.$$

Question 9

The force between two point charges is proportional to which of the following?

Accepted Answer

The product of the magnitudes of the charges.

Question 10

A microwave oven heats food using electromagnetic waves. Why should you not put metal objects inside a microwave?

Accepted Answer

Metal objects can reflect microwaves, causing sparks and possible fire.

Question 11

The electric field due to a group of point charges is calculated by:

Accepted Answer

Adding the vector sum of the electric fields from each charge (superposition).

Question 12

A charge $$+q is $$placed at the origin. A second charge $$+2 	imes 10$$^{-9}$$\,\mathrm{C} is $$placed at $$x = 0.1\,\mathrm{m}. $$What happens to the force on the second charge if its value is doubled?

Accepted Answer

The force also doubles.

Question 13

Which of the following is true about the electric field at a location due to a point charge?

Accepted Answer

It is independent of the charge of the particle used to measure it.

Question 14

A negative charge is placed in a uniform electric field. What is the direction of the force on the charge?

Accepted Answer

Opposite to the direction of the electric field.

Question 15

If the electric field at a point is $$\vec{E}$$, what is the force on a charge $$q$$ placed at that point?

Accepted Answer

$$\vec{F} = q\vec{E}$$

Question 16

Which of the following best describes the units of electric field strength?

Accepted Answer

$$\mathrm{N/C}$$

Question 17

A sphere of charge, a line of charge, and a plane of charge are idealized models used in electrostatics. Which statement is correct about these models?

Accepted Answer

They are useful approximations for calculating electric fields near large or long distributions of charge.

Question 18

If two charges are placed such that the electric field from each points in opposite directions at a certain location, what must be true for the net electric field to be zero at that location?

Accepted Answer

The magnitudes of the electric fields from each charge must be equal.

Electric Forces and Fields: Study Notes

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