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My MCAT PHYSICS > Electrostatics > Flashcards

Electrostatics Flashcards

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1
Q

what is electrostatics?

A

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

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2
Q

mutual attraction of earth and moon

A

eaths attraction tugs on moon and moon tugs on the earth

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3
Q

how is universal law of gravitiy similar to coloums law

A

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

k like g is a constant

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4
Q

Repulsion or attraction

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

A

changing sign for force changes attraction

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

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5
Q

What is Coulombs law?

A

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)

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6
Q

what is an electric field?

A

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.

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7
Q

equation of electric field?

A

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
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8
Q

where does an electric field come from?

A

Divide coloubms law by q to get energy =

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9
Q

describe charges

A

positive charge small q is repelled by big Q positive charge

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10
Q

describe charges

A

positive charge small q is attracted by big Q neg charge

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11
Q

how do we represent a strong electric field?

A

with more lines - more density is stronger field

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12
Q

what happens if we go further from the nucleus?

A

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

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13
Q

What is electric potential energy?

A

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

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14
Q

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

A

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

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15
Q

electric potential energy of opposite charges?

A

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

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16
Q

why is PE neg for opposite charges?

A

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

-25 is colder than -5 (analogy)

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17
Q

What is electric potential?

A

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

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18
Q

What does voltage (electric potential) depend on?

A

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

19
Q

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

A

half as much energy each energy level

20
Q

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

A

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

21
Q

unit of volts

A

J/C

22
Q

how does floursence work with electric fields?

A

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

23
Q

What are the 4 electrostatic equations?

A
24
Q

medical applications of electric charge

A

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

25
Q

contrast gravity and electrostatic force in terms of attraction

A

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

26
Q

what is the coloumn and unit

A

e = 1.60 x 10^-19 C
C units

27
Q

proton and electron charge in C

A

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

28
Q

compare proton and electron charge and mass

A

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

29
Q

describe an insulator

A

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

30
Q

describe a conductor

A

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

31
Q

do neutrons contribute to charge?

A

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

32
Q

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

A

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

33
Q

which are conductors and which are insulators?

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

A

conductors: copper, iron, sulfuric acid, blood

insulators: hair, distilled water, glass

34
Q

how can you tell direction of force?

A

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

35
Q

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

A

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

distance not important

36
Q

What is the convention of electric field lines

A

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

37
Q

How do net electrical fields work?

A

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

38
Q

what is the electric field midpoint of two negative charges?

A

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

same for 2 positive charges

39
Q

what charge creates the electric field?

A

source charge creates electric field

40
Q

electric potential energy increases when..

electric potential energy decreases when..

A

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

41
Q

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

if like charges decrease electrical potential energy then..

A

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

42
Q

Contrast electric potential energy in magnitude and sign

A

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.

43
Q

Full newtowns first law

A

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

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