Electrostatics

Question 1

Full newtowns first law

Answer 1

F = G * (Mm/r^2) ==> attractions between 2 masses

Question 1

what is electrostatics?

Answer 1

Electrostatics is the study of forces between charges, as described by Coulomb’s Law. We develop the concept of an electric field surrounding charges.

Question 2

mutual attraction of earth and moon

Answer 2

eaths attraction tugs on moon and moon tugs on the earth

Question 3

how is universal law of gravitiy similar to coloums law

Answer 3

coloubms law uses charges not masses – force exists between 2 objects

k like g is a constant

Question 4

Repulsion or attraction

positive + positive –>
neg + neg means –>
positive + neg –>

Answer 4

changing sign for force changes attraction

positive + positive –> repulsion
neg + neg means –> repulsuion
positive + neg –> attraction

Question 5

What is Coulombs law?

Answer 5

Coulomb’s law describes the strength of the electrostatic force (attraction or repulsion) between two charged objects. The electrostatic force is equal to the charge of object 1 times the charge of object 2, divided by the distance between the objects squared, all times the Coulomb constant (k).

Fe is the magnitude of the electrostatic force
K is columbs constant (electrostatic const)

Question 6

what is an electric field?

Answer 6

An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles. Charged particles exert attractive forces on each other when their charges are opposite, and repulsion forces on each other when their charges are the same.

Question 7

equation of electric field?

Answer 7

electric field is the force per q charge

Fe is the magnitude of the force felt by test charge q
Q is the source of magnitude

ratio of force per unit charge is constant

• double charge doubles the force it experiences
• note the interconversion

Question 8

where does an electric field come from?

Answer 8

Divide coloubms law by q to get energy =

Question 9

describe charges

Answer 9

positive charge small q is repelled by big Q positive charge

Question 10

describe charges

Answer 10

positive charge small q is attracted by big Q neg charge

Question 11

how do we represent a strong electric field?

Answer 11

with more lines - more density is stronger field

Question 12

what happens if we go further from the nucleus?

Answer 12

decrease in force

As you go farther from the nucleus, electrons at higher levels have more energy, and their energy increases by a fixed, discrete amount. Electrons can jump from a lower to the next higher energy level if they absorb this amount of energy

Question 13

What is electric potential energy?

Answer 13

electric potential energy is the work needed to move a test charge from infinity to a point in space in an electric field with a source charge

U = W = F x r in Joules
U = kQq/r in Joules

radius of charge from center
Force

all the variables that influence force influence energy

Question 14

electric potential energy of two close positive charges and two close negative charges?

Answer 14

High positive PE

for both alike charges ( 2 pos, 2 neg)

the closer they are the less stable because they repel

as they move apart the magnitude of electric potential energy becomes greater and greater positive number

Question 15

electric potential energy of opposite charges?

Answer 15

large Neg PE

the closer they are, the more stable because they attract

energy is increasingly negative as they are brought closer => which is more stable

Question 16

why is PE neg for opposite charges?

Answer 16

as r increases PE is bigger in magnitude –> more neg and it drops

-25 is colder than -5 (analogy)

Question 17

What is electric potential?

Answer 17

aka voltage

you can predict potential energy of second charge given first charge

external work needed to bring a charge from one location to another location in an electric field

Question 18

What does voltage (electric potential) depend on?

Answer 18

bigger Q (source) has greater voltage
greater distance increases voltage

Question 19

How does potential energy change as little q is futher from big q

Answer 19

half as much energy each energy level

Question 20

desribe potential energy effect on pos big Q and neg little q

Answer 20

energy increases when you seperate opposite charges

only need -100 J when we are further than when closer we need -200 J ==> little q gains energy

Question 21

unit of volts

Answer 21

J/C

Question 22

how does floursence work with electric fields?

Answer 22

uv light high energy shines on uranium bumps which increases an electrons energy and moves it away from nucleus

high energy is unstable

electron emits photons to rid of energy

photos are in visible range =-> green

Question 23

What are the 4 electrostatic equations?

Answer 23

Question 24

medical applications of electric charge

Answer 24

cardioversion and defibrillation create strong electrical current through hearts conductive system to resychronize a pulse

Question 25

contrast gravity and electrostatic force in terms of attraction

Answer 25

gravity - attraction of 2 bodies
electrosatic force - depends on charge

Question 26

what is the coloumn and unit

Answer 26

e = 1.60 x 10^-19 C
C units

Question 27

proton and electron charge in C

Answer 27

proton = q = +e
electron = q = -e

Question 28

compare proton and electron charge and mass

Answer 28

same magnitude of charge but not sign
proton has greater mass than electron

Question 29

describe an insulator

Answer 29

will not distribute charge over its surface and will not transfer that charge to another neutral object well or to another insulator
electrons are closely linked with nuclei
most nonmetals are insulators

Question 30

describe a conductor

Answer 30

when a conductor is given a charge the charges will distribute approximately evenly upon the surface. They can transfer and transport charges and are often used in circuits or electrochemical cells.

Nuclei surrounded by a sea of free electrons that rapidly move through the material and are loosely associated with positive charges

usually metals
also ionic electrolye solutions

Question 31

do neutrons contribute to charge?

Answer 31

nope. 1 C of electrons and 3 moles of neutrons will have a net charge only of 1 C of electrons

electrons = -e = -1.6 X 10^-19 C

Question 32

when placed one meter from another, which will experience a greater acceleration: 1 C of electrons or 1 C of protons

Answer 32

F = ma
Force is the same for e and p
but e have much smaller mass so will experience greater acceleration

Question 33

which are conductors and which are insulators?

blood, hair, copper, glass, iron, sulfuric acid, distilled water

Answer 33

conductors: copper, iron, sulfuric acid, blood

insulators: hair, distilled water, glass

Question 34

how can you tell direction of force?

Answer 34

like repel
opposites attract
force points along the line connecting the center of the two charges

Question 35

what happens when a pos and neg charge distance is doubled – how does force change?

Answer 35

distance doubles, square of distance is quadrupled, force is reduced to 1/4 of original

distance not important

Question 36

What is the convention of electric field lines

Answer 36

how a positive charge would move in presence of a source charge ( given as pos or neg)

Question 37

How do net electrical fields work?

Answer 37

every charge exerts its own electric field, a collection of charges will exert an electric field at a point in space that is equal to the vector sum of all electric fields

Question 38

what is the electric field midpoint of two negative charges?

Answer 38

0 because charges are the same and they cancel out –> no field

same for 2 positive charges

Question 39

what charge creates the electric field?

Answer 39

source charge creates electric field

Question 40

electric potential energy increases when..

electric potential energy decreases when..

Answer 40

increase when two like charges move closer
increase when two opposite charges move apart
decrease when two like charges move apart
decrease when two opposite charges move towards eachother

Question 41

what does a decrease in electrical potential energy indicate about system?

if like charges decrease electrical potential energy then..

Answer 41

decrease means its more stable
-4J to -7J means more negative which means more stable

if like charges decrease electrical potential energy then.. the distance increases bc they repell and are more stable that way so PE dec which is good

if opp charges with increase electrical potential energy means distance increases bc they attract and are more stable that way so PE is inc which is bad

Question 42

Contrast electric potential energy in magnitude and sign

Answer 42

otential energy increases in magnitude if it gets further away from zero. This is equivalent to the force between the two charges becoming stronger - regardless of whether it is attractive or repulsive. PE increases in sign if it becomes more positive (and decreases if it becomes more negative). This is equivalent to the force between the two charges becoming less attractive and more repulsive.