Q: Two identical balloons are each charged with $$-6.25\ nC$$ and held $$61.7\ cm$$ apart. What is the magnitude of the electrical force of repulsion between them? ($$k_e = 8.99 \times 10^9$\ N\cdot m^2$/C^2$)

$$F = 9.2 \times 10$$^{-7}$$\ N$$

Question 1

Which of the following best describes the direction of the electric field produced by a negative point charge?

Accepted Answer

It points inward toward the charge.

Question 2

A test charge $$q_0 is $$placed in an electric field $$E$$ and experiences a force $$F_e. $$Which equation correctly defines the electric field at that point?

Accepted Answer

$$E = \frac{F_e}{q_0$}$$

Question 3

Two charges, $$+3\ \mu C$$ and $$-5\ \mu C$$, are separated by $$2$$ meters. What is the magnitude of the electrostatic force between them? ($$k_e = 8.99 	imes 10^9$\ N\cdot m^2$/C^2$)

Accepted Answer

$$F = 3.37\ N$$

Question 4

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

Accepted Answer

They are continuous.

Question 5

A Styrofoam ball of mass $$5.0 	imes 10$$^{-3}$$\ kg$$ carries a charge of $$4.0\ \mu C. $$What upward electric field will balance the weight of the ball? ($$g = 9.8\ m/s^2$)

Accepted Answer

$$1.2 	imes 10^4$\ N/C$$

Question 6

According to Coulomb’s Law, what happens to the force between two point charges if the distance between them is doubled?

Accepted Answer

The force is quartered.

Question 7

Which of the following is the correct expression for the magnitude of the electric force between two point charges $$q_1$$ and $$q_2$$ separated by a distance $$r$$?

Accepted Answer

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

Question 8

Two identical balloons are each charged with $$-6.25\ nC$$ and held $$61.7\ cm$$ apart. What is the magnitude of the electrical force of repulsion between them? ($$k_e = 8.99 	imes 10^9$\ N\cdot m^2$/C^2$)

Accepted Answer

$$F = 9.2 	imes 10$$^{-7}$$\ N$$

Question 9

Which of the following best describes the electric field at the midpoint between two equal and opposite charges $$+Q$$ and $$-Q$$ placed 1 meter apart?

Accepted Answer

Directed toward $$-Q$$

Question 10

Which of the following is true about the forces between two point charges according to Newton’s third law?

Accepted Answer

$$F_{AB} = -F_{BA}$$

Question 11

If the electric field lines are closest together at point A, farther apart at point B, and absent at point C, how do the magnitudes of the electric field at these points compare?

Accepted Answer

A \u003e B \u003e C

Question 12

Which of the following is NOT a property of electric field lines?

Accepted Answer

They always intersect each other.

Question 13

A positive test charge is placed near a negative source charge. What is the direction of the electric force on the test charge?

Accepted Answer

Toward the source charge

Question 14

Which of the following real-life examples involves electric fields?

Accepted Answer

Lightning during a thunderstorm

Question 15

If three charges are aligned as $$q_1 = +2$$\ \mu C$$, q_2$ = -3\ \mu C$$, $$q_3 = +2$$\ \mu C$$, what is the net force on q_2$ if all are equally spaced?

Accepted Answer

The net force is the vector sum of the forces from $$q_1$$ and $$q_3.$$

Question 16

Which of the following best explains why electric field lines never cross?

Accepted Answer

Because the electric field has a unique direction at every point.

Question 17

What is the SI unit of the electric field?

Accepted Answer

Newton per Coulomb ($$N/C)$$

Question 18

Which of the following is a correct statement about the superposition principle for electric forces?

Accepted Answer

The net force on a charge is the vector sum of the forces exerted by all other charges.

Question 19

If the charge on one of two point charges is doubled, how does the force between them change?

Accepted Answer

It doubles.

Electric Field, Electric Force, and Coulomb’s Law: Study Notes

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