Q: Which formula would you use to find the electric field at a point due to several point charges?

$$E_{\text{total}} = \sum_i E_i$$

Q: Which of the following is the correct value for the elementary charge $$e$$?

$$e = 1.602 \times 10$$^{-19}$$ C

Question 1

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

Accepted Answer

The total electric charge in any isolated system remains constant; charge cannot be created or destroyed.

Question 2

A dust speck with mass $$2.0\$$times10^{-6}$$ kg and charge 1.0$$\$$times10^{-6} C is $$placed in an electric field of $$10 N/C. $$What is its acceleration?

Accepted Answer

$$a = 5,000 m/s$^2$$

Question 3

Which equation correctly expresses Coulomb’s law for the magnitude of the electric force between two point charges $$q_1$$ and $$q_2$$ separated by distance $$r$$?

Accepted Answer

$$F = k\dfrac{q_1q_2}{r^2$}$$

Question 4

If two pith balls of equal mass are charged and hang on strings, repelling each other, what can you conclude about the signs of their charges?

Accepted Answer

Both must have the same sign, either both positive or both negative.

Question 5

What is the electric field at a point $$P$$ due to a single point charge $$Q$$ located a distance $$r$$ away?

Accepted Answer

$$E = k\dfrac{Q}{r^2$}$$

Question 6

A helium atom loses an electron. What is its resulting charge?

Accepted Answer

It becomes positively charged.

Question 7

Which of the following best describes the difference between electric force and electric field?

Accepted Answer

Electric force is the interaction between two charges, while electric field is the force per unit charge at a point in space.

Question 8

If you place a third charge between two point charges $$Q$$ and $$16Q$$ separated by distance $$d$$, at what distance $$x$$ from $$Q$$ should you place it so the net force on it is zero?

Accepted Answer

$$x = \dfrac{d}{5}$$

Question 9

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

Accepted Answer

All known charges are integer multiples of $$e/3.$$

Question 10

A ball with charge $$Q is $$replaced by a rod of 10 smaller balls, each with charge $$Q/10. $$How does the electric force on a nearby ball compare to the original force?

Accepted Answer

The rod and the original ball exert the same magnitude force if their total charge is the same and are at the same distance.

Question 11

What is the SI unit of electric charge?

Accepted Answer

Coulomb (C)

Question 12

If the electric field at a point is $$E$$ and a charge $$q is $$placed at that point, what is the force experienced by the charge?

Accepted Answer

$$F = qE$$

Question 13

Which of the following is a property of electric dipoles?

Accepted Answer

They consist of two equal and opposite charges separated by a distance.

Question 14

If a proton and an electron are placed near each other, what type of force do they experience?

Accepted Answer

An attractive electric force.

Question 15

Which of the following best describes how electric fields from multiple point charges combine?

Accepted Answer

Electric fields add as vectors; the total field is the vector sum of the individual fields.

Question 16

A test charge $$q is $$placed at point $$P in $$the presence of several other charges. The net electric field at $$P is$$ $$E. $$What is the net force on the test charge?

Accepted Answer

$$F = qE$$

Question 17

Which of the following is NOT a goal of the chapter?

Accepted Answer

Calculate the magnetic field due to moving charges.

Question 18

If a neutral atom loses an electron, what happens to its charge?

Accepted Answer

It becomes positively charged.

Question 19

Which formula would you use to find the electric field at a point due to several point charges?

Accepted Answer

$$E_{	ext{total}} = \sum_i E_i$$

Question 20

Which of the following is the correct value for the elementary charge $$e$$?

Accepted Answer

$$e = 1.602 	imes 10$$^{-19}$$ C

Electric Charge and Electric Forces: Study Notes

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