Q: What is the value of the Coulomb constant $$k_e$$?

$$k_e = 9.0 \times 10^9$ \ \mathrm{N \cdot m^2$ / C^2$}$$

Question 1

Which equation describes the magnitude of the electric field created by a point charge at a distance $$r$$ from the charge?

Accepted Answer

$$|\vec{E}| = \dfrac{k_e |q|}{r^2$}$$

Question 2

What is the value of the Coulomb constant $$k_e$$?

Accepted Answer

$$k_e = 9.0 	imes 10^9$ \ \mathrm{N \cdot m^2$ / C^2$}$$

Question 3

Two point charges, $$+Q$$ and $$-Q$$, are placed a distance $$d$$ apart. What is the direction of the electric field at a point exactly midway between them?

Accepted Answer

Toward the $$-Q$$ charge

Question 4

Which principle allows you to calculate the net electric field from multiple point charges?

Accepted Answer

The principle of superposition

Question 5

A charge $$q is $$placed in an electric field $$\vec{E}. $$What is the force $$\vec{F}$$ experienced by the charge?

Accepted Answer

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

Question 6

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

Accepted Answer

The density of field lines represents the strength of the field

Question 7

In a region of uniform electric field, what is the direction of the force on an electron?

Accepted Answer

Opposite to the direction of the electric field

Question 8

Two small metallic spheres, each of mass $$0.2 g$$, are suspended by light strings of length $$L. $$The spheres are given the same charge of $$7.2 nC $$and come to equilibrium when each string is at an angle of $$5^	ext{o}$$ from the vertical. Which forces must be considered to solve for $$L$$?

Accepted Answer

Gravitational force and electric force

Question 9

Which equation describes the magnitude of the gravitational field created by a point mass $$m at a $$distance $$r$$?

Accepted Answer

$$|\vec{g}| = \dfrac{Gm}{r^2$}$$

Question 10

If two point charges are placed near each other, what happens to the electric field at a point in space due to these charges?

Accepted Answer

The fields must be added as vectors

Question 11

A third charge is placed somewhere along the line joining $$-2Q$$ and $$+Q. On $$which segment could the net force on this third charge be zero?

Accepted Answer

Somewhere in segment A (left of $$-2Q)$$

Question 12

Which of the following is NOT a rule for drawing electric field lines?

Accepted Answer

Field lines represent the trajectory of charged particles

Question 13

What is the main limitation of Coulomb's Law?

Accepted Answer

It only applies to point charges or outside uniform spheres/shells of charge

Question 14

Which real-world device uses a uniform electric field for its operation?

Accepted Answer

A camera flash

Question 15

If the electric field lines are denser at point A than at point B, what can be said about the electric field strength at these points?

Accepted Answer

The field strength is stronger at A than at B

Question 16

Which analogy is correct between gravitational and electric fields?

Accepted Answer

Both fields follow an inverse-square law

Question 17

A positive charge is placed in an electric field. What is the direction of the force on the charge?

Accepted Answer

In the direction of the electric field

Question 18

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

Accepted Answer

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

Question 19

What is the main difference between the direction of gravitational and electric fields?

Accepted Answer

Gravitational fields point toward mass, electric fields point away from positive and toward negative charges

Question 20

Which statement about the superposition principle is correct?

Accepted Answer

Fields from separate sources can be treated independently and added as vectors

Electric Fields from Point Charges and Coulomb's Law: Study Notes

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