Q: What is the net charge (in Coulombs) of an atom with 16 protons and 7 electrons?

$$9 \times 1.6 \times 10$$^{-19}$$\ \mathrm{C}$$

Q: A $$1.5\ \mu\mathrm{C}$$ charge with a mass of $$50\ \mathrm{g} is in an $$electric field that perfectly balances its gravity. What is the magnitude of the electric field?

$$\dfrac{mg}{q} = \dfrac{0.05 \times 9.8}{1.5 \times 10$$^{-6}$$} = 3.27 \times 10$$^{5}$$\ \mathrm{N/C}$$

Question 1

What is the net charge (in Coulombs) of an atom with 16 protons and 7 electrons?

Accepted Answer

$$9 	imes 1.6 	imes 10$$^{-19}$$\ \mathrm{C}$$

Question 2

How many electrons are needed to make up a charge of $$-1.5 	imes 10$$^{-5}$$\ \mathrm{C}$$?

Accepted Answer

$$9.4 	imes 10$$^{13}$$

Question 3

Which of the following best describes the process of charging by induction?

Accepted Answer

Charging an object without direct contact by bringing a charged object near it and grounding the object

Question 4

A neutral metal sphere is grounded and a negatively charged rod is brought near (but not touching). What happens to the charges in the sphere?

Accepted Answer

Electrons flow from the sphere to the ground, leaving the sphere positively charged

Question 5

Two identical metal balls are placed in an insulated box. Initially, one has a charge of $$1\ \mathrm{C}$$ and the other $$-3\ \mathrm{C}. $$After some time, the charge on the first ball is $$-2\ \mathrm{C}. $$What is the charge on the second ball?

Accepted Answer

$$0\ \mathrm{C}$$

Question 6

Which of the following statements about conductors and insulators is correct?

Accepted Answer

Conductors allow electrons to move freely, while insulators do not allow electrons to move freely.

Question 7

A $$2\ \mathrm{C}$$ and a $$3\ \mathrm{C}$$ charge are separated by a distance such that the electric field at the $$2\ \mathrm{C}$$ charge is $$10\ \mathrm{N/C}. $$What is the force on the $$2\ \mathrm{C}$$ charge?

Accepted Answer

$$20\ \mathrm{N}$$

Question 8

If the force between two charges is $$F$$ when the distance is $$d$$, what will the force be if the distance is doubled to $$2d$$?

Accepted Answer

$$\dfrac{F}{4}$$

Question 9

A $$1.5\ \mu\mathrm{C}$$ charge with a mass of $$50\ \mathrm{g} is in an $$electric field that perfectly balances its gravity. What is the magnitude of the electric field?

Accepted Answer

$$\dfrac{mg}{q} = \dfrac{0.05 	imes 9.8}{1.5 	imes 10$$^{-6}$$} = 3.27 	imes 10$$^{5}$$\ \mathrm{N/C}$$

Question 10

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

Accepted Answer

Outward in all directions from the charge

Question 11

What is the formula for the electric field $$E at a $$distance $$r$$ from a point charge $$Q$$?

Accepted Answer

$$E = \dfrac{kQ}{r^2$}$$

Question 12

A dipole consists of charges $$+q$$ and $$-q$$ separated by distance $$d. $$What is the magnitude of its dipole moment?

Accepted Answer

$$p = qd$$

Question 13

A dipole is placed in a uniform electric field $$E at an $$angle $$	heta to $$the field. What is the magnitude of the torque on the dipole?

Accepted Answer

$$	au = pE\sin	heta$$

Question 14

Two charges, $$2\ \mathrm{C}$$ and $$-3\ \mathrm{C}$$, are placed $$7\ \mathrm{cm}$$ apart on the x-axis. At what point on the x-axis is the electric field zero?

Accepted Answer

To the right of the $$-3\ \mathrm{C}$$ charge, at a distance $$x$$ such that $$\dfrac{2}{(x+0.07)^2$} = \dfrac{3}{x^2$}$$

Question 15

If two identical charges are connected by a $$5\ \mathrm{cm}$$ wire with a $$10\ \mathrm{N}$$ tension, what is the magnitude of each charge?

Accepted Answer

$$q = \sqrt{\dfrac{F r^2$}{k}}$$

Question 16

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

Accepted Answer

Charge can be moved from one object to another but cannot be created or destroyed.

Question 17

A $$-1\ \mathrm{C}$$ charge is placed between a $$1\ \mathrm{C}$$ and a $$2\ \mathrm{C}$$ charge as shown: $$1\ \mathrm{C} ---4cm$$--- $$-1\ \mathrm{C} ---6cm$$--- $$2\ \mathrm{C}. $$What is the direction of the net force on the $$-1\ \mathrm{C}$$ charge?

Accepted Answer

To the right, toward the $$2\ \mathrm{C}$$ charge

Question 18

What is the direction of the net force on a $$1\ \mathrm{C}$$ charge placed at the center of a square with $$2\ \mathrm{C}$$ charges at each corner?

Accepted Answer

The net force is zero due to symmetry

Question 19

Which pair of charges in an equilateral triangle with charges $$2e$$, $$e$$, and $$3e at $$the vertices will experience the greatest electric force?

Accepted Answer

The pair $$2e$$ and $$3e$$

Electric Charge, Forces, and Fields: Study Notes for College Physics

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