Physics IV: Electrostatics, Batteries, Capacitors, Resistors

Question 1

the attractive force holding together the nucleus is directly caused by

Answer 1

electric charge, both positive and negative

Question 2

charge of a proton is called the ______________ and is designated by the symbol ____. Its value is __________ C (coulombs)

Answer 2

“elementary charge”

symbol: +e
value: e=1.6 x 10^-19 C

Question 3

if a neutral atom has electrons removed/added/both we say it has been ionized

Answer 3

both, and the resulting atom is an ion

Question 4

what does it mean to say that charge is “quantized”

Answer 4

it means that an object can be charged by losing or gaining electrons or protons in whole number amounts.

so, q=n(±e)

^q=charge

^{n= 0, 1, 2, …}

Question 5

How do you find the charge of any ion in Coulombs?

Answer 5

Example: Flourine

take its simplified charge: -1 →means -1e → means -1 elementary units → so multiply -1 x unit of elementary unit → -1 x 1.6 x 10^-19 → -1.6 x 10^-19 ​

for a positively charged atom like

Ca²⁺ it’s +2 x 1.6 x 10^-19 ​→ +3.2 x 10^-19

Question 6

What’s Coulombs law and what does it mean?

Answer 6

F_e=k |q₁q₂| /r² (in Newtons)

It means that the magnitude of the electrostatic force is proportional to the absolute value of the charges (q₁q₂) and inversely proportional to r²

when the material between the charges is air, then k is Coulomb’s constant, which is 9 x 10⁹ N•m²/C²

*in problems, assume K is coulombs constant unless specified otherwise

Each particle feels the same force (F_e) toward or against one another

*picture shows its similartiy to newton’s law

Question 7

as a smaller object moves away from a larger object d/t repulsion, the object’s acceleration will increase/decrease

Answer 7

decrease because electrostatic force is inversely proportional to the square of the distance between the charges and as a smaller object moves away from the larger object (in a repulsion scenario) the distance increases which weakens the electrostatic force/force of repulsion _{in this case}

F proportional to acceleration, so if force decreases so will acceleration

*note that velocity is increasing because it remains in movement in the same vector as before, away from the larger body, but the rate at which it increases slows

Question 8

how do you determine the net electric force on a charge (q) due to a collection of other charges (Qs)

Answer 8

it is equal to the vector sum of the individual forces that each of the charges (Qs) alone exerts on q

Question 9

Which of the following pairs of electric forces form an action-reaction pair? (can pick more than one)

I. 2 positive charges of different masses placed at a distance d apart

II. 2 negative charges of equal masses placed at a distance d apart

III. one positive charge and one negative charge of equal masses placed at a distance d apart

Answer 9

All of them.

Question 10

T/F: The electric field inside of an electrostatic conductor is always zero

Answer 10

true

Question 11

Moving from higher electric potential (V or φ) to lower electric potential, you get a increase/decrease in PE (-ΔPE)

Answer 11

decrease (analogous to the PE that decreases when you drop a book from a height)

Question 12

For an electron, the move towards higher potential φ (ie higher voltage), is favorable/unfavorable, because then Δφ is positive (+), which yields a negative ΔPE in the equation:

ΔPE=qΔφ

Answer 12

favorable because -ΔPE always represents movement with nature which is favored

Question 13

within a conductor, if a voltage is not applied, then there is no net movement of electrons, meaning that they are freely moving, but in random directions such that the directions all cancel out. What does it look like to apply a voltage?

Answer 13

Question 14

how is current measured

Answer 14

since current is the flow of charge, we use a version of flow rate equation f=Av:

I=Q/t

Q=charge in coulombs

t=time

I= current