Q: Calculate the number of electrons in 2.0 kg of electrons. (Mass of electron $$m_e = 9.11 \times 10$$^{-31}$$ kg)

$$n = \frac{2.0}{9.11 \times 10$$^{-31}$$} = 2.20 \times 10$$^{30}$$

Question 1

Which statement best describes the electrical nature of matter?

Accepted Answer

Matter is electrically neutral in general, but electrons are mobile and can be separated from atoms.

Question 2

A glass rod is rubbed with silk. What type of charge does the glass rod acquire, and why?

Accepted Answer

Positive, because electrons are transferred from the glass rod to the silk.

Question 3

Calculate the number of electrons in 2.0 kg of electrons. (Mass of electron $$m_e = 9.11 	imes 10$$^{-31}$$ kg)

Accepted Answer

$$n = \frac{2.0}{9.11 	imes 10$$^{-31}$$} = 2.20 	imes 10$$^{30}$$

Question 4

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

Accepted Answer

Conductors have free electrons that can move throughout the material.

Question 5

A metal sphere is given excess charge. Where does the excess charge reside?

Accepted Answer

On the surface of the sphere.

Question 6

Which equation correctly expresses Coulomb's Law for the force between two point charges?

Accepted Answer

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

Question 7

If three point charges are placed on the x-axis, how do you determine the net force on one of the charges?

Accepted Answer

Add the forces as vectors using the principle of superposition.

Question 8

A point charge $$q = +10 \mu C is $$located at the origin. What is the direction of the electric field at a point on the positive x-axis?

Accepted Answer

Away from the origin.

Question 9

Which formula gives the electric field due to a point charge at a distance $$r$$?

Accepted Answer

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

Question 10

A parallel-plate capacitor has plates separated by distance $$d$$ and carries charges $$+Q$$ and $$-Q. $$What is the direction of the electric field between the plates?

Accepted Answer

From the positive plate to the negative plate.

Question 11

Which statement about electric field lines is correct?

Accepted Answer

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

Question 12

A conductor is placed in an external electric field. What happens to the electric field inside the conductor when charges are at rest?

Accepted Answer

The electric field inside the conductor is zero.

Question 13

Which of the following is true about the process of charging a conductor by induction?

Accepted Answer

It requires grounding the conductor to allow like charges to leave.

Question 14

What is the value of the elementary charge $$e$$?

Accepted Answer

$$e = 1.60 	imes 10$$^{-19}$$ C

Question 15

A spherical charge distribution behaves from the outside as though:

Accepted Answer

The total charge is concentrated at the center of the sphere.

Question 16

Which equation correctly relates electric flux $$\Phi_E$$ through a surface to the electric field $$E$$ and area $$A$$?

Accepted Answer

$$\Phi_E = EA \cos 	heta$$

Question 17

According to Gauss's Law, the electric flux through a closed surface is proportional to:

Accepted Answer

The total charge enclosed by the surface.

Question 18

Which of the following is a property of semiconductors?

Accepted Answer

Their properties change with chemical composition.

Question 19

A charged rod is brought near a neutral insulator. What happens to the atoms in the insulator?

Accepted Answer

They rotate and become polarized, producing an excess of opposite charge on the surface.

Question 20

If the surface of a conductor is sharply curved, what happens to the electric field at that location?

Accepted Answer

The electric field is stronger at the sharp curve.

Chapter 19: Electric Charges, Forces, and Fields – Structured Study Notes

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