Q: A plate carries a charge of $$-3.0\ \mu\text{C}$$, while a rod carries a charge of $$+2.0\ \mu\text{C}. $$How many electrons must be transferred from the plate to the rod so that both objects have the same charge?

$$3.13 \times 10$$^{13}$$ electrons

Q: A small sphere of mass $$5.10\ \text{g} is $$hanging vertically from an insulating thread that is $$12.0\ \text{cm}$$ long. It is subjected to a horizontal electric field of $$7.20 \times 10^5$\ \text{N/C}$$ and is displaced $$6.00\ \text{cm}$$ horizontally. What is the angle $$\theta$$ that the thread makes with the vertical?

$$\theta = \arctan\left(\frac{6.00\ \text{cm}}{12.0\ \text{cm}}\right) = 26.6^\circ$$

Question 1

A balloon is rubbed against a person's hair, causing the hair to stand up as shown in the image. Which principle best explains why the hair is attracted to the balloon?

Accepted Answer

Electrons are transferred from the hair to the balloon, making the balloon negatively charged and the hair positively charged, resulting in attraction due to opposite charges.

Question 2

According to Table 16.1, what is the electric charge of a neutron?

Accepted Answer

$$q_n = 0$$

Question 3

Which of the following statements about the conservation of electric charge is correct?

Accepted Answer

The net charge of a closed system never changes.

Question 4

A metal sphere is charged by touching it with a glass rod that has been rubbed with silk. What type of charging process is this?

Accepted Answer

Charging by contact

Question 5

Which material is most likely to conduct electric charge efficiently?

Accepted Answer

Copper

Question 6

A glass rod is rubbed with a silk cloth. What happens to the charges on the rod and the cloth?

Accepted Answer

The rod becomes positively charged and the cloth becomes negatively charged.

Question 7

Which equation represents Coulomb’s law for the force between two point charges?

Accepted Answer

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

Question 8

Two point charges, $$q_1 = +2.0$$\ \mu	ext{C}$$ and q_2$ = -2.0\ \mu	ext{C}$$, are placed 0.5 m apart. What is the direction of the force on $$q_1$$ due to $$q_2$$?

Accepted Answer

Toward $$q_2$$

Question 9

A plate carries a charge of $$-3.0\ \mu	ext{C}$$, while a rod carries a charge of $$+2.0\ \mu	ext{C}. $$How many electrons must be transferred from the plate to the rod so that both objects have the same charge?

Accepted Answer

$$3.13 	imes 10$$^{13}$$ electrons

Question 10

Which statement about electric field lines is correct?

Accepted Answer

Electric field lines start on positive charges and end on negative charges.

Question 11

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

Accepted Answer

$$E = \frac{k|Q|}{r^2$}$$

Question 12

A small sphere of mass $$5.10\ 	ext{g} is $$hanging vertically from an insulating thread that is $$12.0\ 	ext{cm}$$ long. It is subjected to a horizontal electric field of $$7.20 	imes 10^5$\ 	ext{N/C}$$ and is displaced $$6.00\ 	ext{cm}$$ horizontally. What is the angle $$	heta$$ that the thread makes with the vertical?

Accepted Answer

$$	heta = \arctan\left(\frac{6.00\ 	ext{cm}}{12.0\ 	ext{cm}}ight) = 26.6^\circ$$

Question 13

If two Styrofoam balls of equal mass are suspended and charged so that they hang apart at equal angles to the vertical, what can be inferred about the signs of their charges?

Accepted Answer

The charges must be the same in sign.

Question 14

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

Accepted Answer

Field lines can form closed loops.

Question 15

Three point charges are placed at the corners of a rectangle. What is the electric field at the fourth corner due to these charges?

Accepted Answer

The electric field is the vector sum of the fields due to each charge.

Question 16

Two positive point charges, $$q_1 = +16$$\ \mu	ext{C}$$ and q_2$ = +4.0\ \mu	ext{C}$$, are separated by $$3.0\ 	ext{m}. At $$what distance from $$q_2$$ along the line joining the charges is the net electric field zero?

Accepted Answer

$$2.25\ 	ext{m}$$

Question 17

A test charge $$q is $$placed in an electric field $$E. $$What is the force experienced by the test charge?

Accepted Answer

$$F = qE$$

Question 18

Which scenario best illustrates the principle of superposition for electric fields?

Accepted Answer

The electric field at a point is the vector sum of the fields from each charge.

Question 19

If the electric field lines are closer together in a region, what does this indicate about the strength of the electric field?

Accepted Answer

The electric field is stronger in that region.

Electric Forces and Fields: Study Notes for College Physics

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