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Malika Physics MCAT > Electrostatics & Magnetism > Flashcards

Electrostatics & Magnetism Flashcards

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1
Q

Calculating electric field (E)

A

E = F/q
F is the electrostatic force experienced by a charged particle
q is the charge of the particle
SI Unit: N/C

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2
Q

Electrons are free to move in a (conductor/insulator)

A

conductor; they distribute evenly over the surface
Example: metals

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3
Q

Insulator

A

Electron’s don’t move, charges don’t distribute evenly over surface
Example: nonmetals

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4
Q

SI unit of charge

A

coulomb (C)

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5
Q

Charge of an electron & proton

A

e = -1.6 x 10^-19 C
p = +1.6 x 10^-19 C

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6
Q

True or false: A neutral object is made of an equal amount of positive and negative charge.

A

True

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7
Q

Can a charged object attract a neutral object?

A

Yes.

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8
Q

Coulomb’s Law (calculating electrostatic force on a particle)

A

F = (Kq1q2)/r^2
K is the electrostatic constant:
9.0 x10^9 N*m^2/C^2

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9
Q

Remember, even if the charges of the two objects aren’t equal. The force that object 1 exerts on the object 2 = force object 2 exerts on object 1

A
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10
Q

Relationship between distance and electrostatic force:

A

Inverse relationship; F = 1/r^2
As distance increases x2, force goes down by 4

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11
Q

Additional things to know about electric field:
Electric field vectors always point away from regions of higher voltage to lower voltage.

A

-Electric field vectors always point away from regions of higher voltage to lower voltage.
-The electric field induces positive particles to move in the same direction as the E field & negative particles to move in opposite directions as E field lines

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12
Q
A
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13
Q

Question from PHYS Lecture:

A
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14
Q

Diagram of electric field on a positive charge

A
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15
Q

Diagram of electric field on a negative charge

A
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16
Q

Calculating electric field of a point charge: (any point in the field)

A

E = (K*|q|)/r^2
q is absolute value of charge on the particle
r is the distance between the charged particle and the particular point in the electric field

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17
Q

If the charged particle is negative, the vectors in the electric field point (away/towards) the particle.

A

negative = towards
positive = away

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18
Q

What is a parallel plate capacitor?

A

Two plates of opposite charges parallel to each other which create a uniform electric field (E).
E travels from positive plate to negative plate.

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19
Q

Calculating electric field (E) in a parallel plate capacitor

A

E = Q/ε0A
ε0 is a constant:
8.85 x 10^-12 C^2/N*m^2
Q is the charge of the capacitor
A is the area of the capacitor

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20
Q

Electric force and electric field are (scalars/vectors) while electric potential energy and electric potential are (scalars/vectors).

A

vectors, scalars

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21
Q

As a proton enters a parallel plate capacitor from the positive plate, how does its electric potential energy and kinetic energy change?

A

∆K increases, ∆U decreases as it moves to the negative plate

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22
Q

As an electron enters a parallel plate capacitor from the positive plate, how does its electric potential energy and kinetic energy change?

A

∆K decreases, ∆U increases because the electron doesn’t want to move towards the negative end, so its speed slows down

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23
Q

Calculating electrostatic force of a parallel plate capacitor

A

Felectro = q*Electric field

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24
Q

Calculating electric potential energy of 1 electron/proton

A

∆U = q * ∆V
∆V is the electric potential difference/change: Vfinal - Vinitial

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25
Q

Protons spontaneously move from (high/low) electric potential to (high/low) electric potential.

A

Move from higher to lower electric potential.
*Spontaneous means W=0

26
Q

Electrons spontaneously move from (high/low) electric potential to (high/low) electric potential.

A

Move from lower to higher electric potential
*Spontaneous means W=0

27
Q

Energy of conservation for electric potential

A

∆K + ∆Uelectric = W

28
Q

Electric potential energy conservation problem

A
29
Q

Calculating electric potential (V) by a point charge

A

∆V = Kq/r

30
Q

Electric potential is inversely related to distance of point charge

A

The further the charge gets, the more the electric potential decreases

31
Q

Calculating electric potential (V) inside a capacitor

A

∆V = E x d
d is the distance between two plates
E is the electric field inside the capacitor
*Can also use this equation to calculate electric field

32
Q

Calculating electric potential energy between 2 point charges

A

∆U = (Kq1q2)/r
K is the electrostatic constant:
9.0 x10^9 N*m^2/C^2

33
Q

Trend:
A proton moving from high –> low electric potential, ALWAYS decreases its electric potential energy.
An electron moving from high –> low electric potential, ALWAYS increases its electric potential energy.

A
34
Q

Equipotential lines

A

-Patterns of lines which represent the electric potential.
-The further the lines are from the charged particle, the lower the electric potential.
-Equipotential lines have equal potential differences between (every increases by 50V)

35
Q

True or false:
Electric field lines are always perpendicular to equipotential lines.

A

Yes they are perpendicular, and point in the direction of high EP to low EP

36
Q
A

*Note here, the distance between equipotential lines decreases, which means electric field vector increases
*Electric field always points in the direction of lower voltage

37
Q

Photoelectric effect

A

The ejection of electrons from a substance due to the absorption electromagnetic radiation.

38
Q

True or false
For the ejection of an electron to occur, the absorbed electromagnetic radiation (E) must exceed the work function (W)

A
39
Q

Equation relating E, W, and kinetic energy

A

(1/2)mv^2 = E - W
or
(1/2)mv^2 = hf - W

40
Q

Kinetic energy of an electron increases when E is (greater than, less than, equal to) W.

A

E is greater than W.

41
Q

True or false:
Frequency of the wave absorbed by the electron is directly proportional to its kinetic energy.

A

True

42
Q

Magnetic field

A

Field created by a moving charge, originates at North pole and travels to South pole
Unit: Tesla
SI Unit: 1 Ns/mC

43
Q

Diamagnetic

A

Atoms only have paired electrons, no net magnetic field, slightly repelled by magnet
Example: wood, plastic, water, glass

44
Q

Paramagnetic

A

Atoms which have unpaired electrons
Example: aluminum, gold, copper

45
Q

Lorentz force equation

A

Sum of the electrostatic and magnetic forces acting on a body

46
Q

Equation for magnetic force on a particle in magnetic field

A

Magnetic force = qvBsinθ

θ is the angle between velocity vector and magnetic field vector

47
Q

right-hand-rule #3
(determines magnetic force)

A
48
Q

Additional things to know:

A

-Magnetic force is perpendicular to the plane of the velocity and magnetic field vectors
-Magnetic force does NO work on a charged particle
-Magnetic force only affects the direction of the particle, it doesn’t alter the KE or the speed

49
Q

When is the magnetic force 0?

A
  1. When the charged particle is at rest (it’s not moving).
  2. When the charged particle is moving parallel to the magnetic field (θ=0˚)
  3. When the charged particle moves completely opposite of mag. field (θ=180˚)
50
Q

In which of the situations is the magnitude of the magnetic force maximum?

A

B. 90˚ angle between velocity vector & magnetic field vector

51
Q

Equation for a charged particle moving in a circular motion

A

r = mv/qB

r is the radius of the particle’s path
m is mass of particle
q is charge of particle
B is magnetic field of particle

52
Q

For a charged particle traveling a circular path, magnetic force always points inward towards the center of the circle.

A
53
Q

Based on the direction of velocity and magnetic field vectors given, how do you determine the charge of the particle traveling in a circular path?

A

Do RHR#3.
If magnetic force points towards center of circle, charge is positive.
If magnetic force points outwards from the circle, charge is negative.

54
Q

How do magnetic fields apply to mass spectrometers?

A

Ions with different masses which enter the spectrometer follow paths of different radii. Only some ions reach the exit slit to continue on to the actual detector.

55
Q

RHR2

A

Point thumb towards direction of traveling current and curl fingers around wire.
Fingers can curl either CW or CCW.
x is into the page, simple dot is out of the page

56
Q

Equation for magnetic force on straight current-carrying wire

A

Magnetic force = ILBsinθ

I is current in the wire
L is length of wire (m)
B is magnetic field (T)
θ is angle between wire and B
For direction of magnetic force, use RHR#3

57
Q

Equation for magnetic field of straight current wire

A

B = µ0*I/2πr

µ0 is 4π x 10^-7
r measured in (m)
For direction of magnetic field, use RHR#2

58
Q

For a straight current wire, what if you aren’t given direction of magnetic field and you need to figure it out?

A

Use RHR#2.
Draw the arrows around the wire pointing in either the determined CW or CCW from the rule.

*On different sides of the wire, the direction of mag. field is different.
*“The page” is always on the right side of the wire for reference

59
Q

Tips to memorize for determining mag. field w/o doing RHR2 (its so confusing)

A

Current in horizontal direction:
Current points right - Above the wire is out of page
Current points left - Above the wire is into page

Current in vertical direction:
Current points up - On right of wire is into the page
Current points down - On right of wire is out of page

60
Q

True or false
If Fnet = 0, magnetic force and electrostatic force should cancel.

A

True

61
Q

Equation for magnetic field of a current loop wire

A

B = µ0*I/2r

µ0 is 1.26 x 10^-6 T*m/A
r measured in (m)

62
Q

Magnetic force between parallel wires/loops

A

If current points in same direction, they attract each other.
If current points in diff. directions, they repel each other.

Malika Physics MCAT (10 decks)

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