Q: A neutral lithium atom has 3 protons, 4 neutrons, and 3 electrons. If it loses one electron, what is its net charge?

$$+1.602 \times 10$$^{-19}$$\ \mathrm{C}$$

Question 1

Which of the following statements best describes the principle of conservation of electric charge?

Accepted Answer

The algebraic sum of all electric charges in any closed system is constant.

Question 2

A neutral lithium atom has 3 protons, 4 neutrons, and 3 electrons. If it loses one electron, what is its net charge?

Accepted Answer

$$+1.602 	imes 10$$^{-19}$$\ \mathrm{C}$$

Question 3

Which of the following materials is a good conductor of electricity?

Accepted Answer

Copper

Question 4

A negatively charged plastic rod is brought near a neutral metal ball suspended by an insulating stand. What happens to the charges in the metal ball?

Accepted Answer

Electrons in the ball are repelled away from the rod.

Question 5

Which process describes charging a neutral conductor by bringing a charged object near it and then grounding the conductor?

Accepted Answer

Charging by induction

Question 6

According to Coulomb’s law, what is the magnitude of the electric force between two point charges $$q_1$$ and $$q_2$$ separated by a distance $$r$$?

Accepted Answer

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

Question 7

A small plastic sphere charged to $$-12\ \mathrm{nC} is $$held $$1.0\ \mathrm{cm}$$ above a small glass bead at rest on a table. The bead has a mass of $$15\ \mathrm{mg}$$ and a charge of $$+10\ \mathrm{nC}. $$What is the direction of the net electric force on the glass bead?

Accepted Answer

Upward, toward the plastic sphere

Question 8

Which statement correctly distinguishes between electric force and electric field?

Accepted Answer

Electric field is a property of space due to a charge, while electric force is the interaction between charges.

Question 9

What is the definition of the electric field $$\vec{E} at a $$point in space?

Accepted Answer

$$\vec{E} = \dfrac{\vec{F}}{q}$$, where $$\vec{F} is $$the force on a test charge $$q at $$that point.

Question 10

A positive point charge $$Q$$ creates an electric field at a distance $$r$$ from itself. What is the magnitude of the electric field at that point?

Accepted Answer

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

Question 11

If a negative test charge is placed in an electric field produced by a positive point charge, in which direction does the force on the test charge point?

Accepted Answer

Opposite to the direction of the electric field

Question 12

Which of the following best describes the superposition principle for electric fields?

Accepted Answer

The total electric field at a point is the vector sum of the fields due to all charges.

Question 13

A uniformly positive charge is distributed around a semicircle. What is the direction of the electric field at the center of curvature?

Accepted Answer

In the $$+y-$$direction

Question 14

Two infinite plane sheets with uniform surface charge densities $$+\sigma$$ and $$-\sigma$$ are placed parallel to each other with separation $$d. $$Where is the total electric field greatest in magnitude?

Accepted Answer

Halfway between the two sheets

Question 15

Which statement about electric field lines is correct?

Accepted Answer

Electric field lines never intersect; at every point, the field has a unique direction.

Question 16

In the illustration of electric field lines due to three point charges, where is the electric field strongest?

Accepted Answer

Where adjacent field lines are closest together.

Question 17

A negatively charged comb can pick up small bits of neutral paper. What physical process allows this to happen?

Accepted Answer

Polarization of the paper molecules

Question 18

Which of the following is true about the quantization of electric charge?

Accepted Answer

All observable charge is an integer multiple of $$e = 1.602 	imes 10$$^{-19}$$\ \mathrm{C}.$$

Question 19

Which scenario best illustrates charging by friction?

Accepted Answer

Rubbing a plastic rod with fur and observing it repel another charged rod.

Electric Charge and Electric Field: Study Notes

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