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Physics 1202Q > Chapter 19 > Flashcards

Chapter 19 Flashcards

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1
Q

Types of Charges

A

They are called positive and negative

Named by Benjamin Franklin

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2
Q

Like vs Opposite charge

A

Like charges repel and unlike charges attract one another

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3
Q

Electric charge is always _____

A

conserved

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4
Q

Charge is not created, only ________

A

exchanged

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5
Q

Objects become charged because ______

A

negative charge is transferred from one
object to another

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6
Q

Charge is quantized

A

All charge is a multiple of a fundamental unit of charge, symbolized by e,
with the value of
e = 1.6 x 10-19 C

o Quarks are the exception
o Electrons have a charge of –e
o Protons have a charge of +e
o The SI unit of charge is the Coulomb (C)

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7
Q

Conductors

A

are materials in which the electric charges move freely in response to an electric force

o Copper, aluminum and silver are good conductors

o When a conductor is charged in a small region, the charge readily distributes itself over the entire surface of the material

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8
Q

Insulators

A

are materials in which electric charges do not move freely

o Glass and rubber are examples of insulators

o When insulators are charged by rubbing, only the rubbed area becomes
charged

o There is no tendency for the charge to move into other regions of the
material

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9
Q

Semiconductors

A

The characteristics of semiconductors are between
those of insulators and conductors

o Silicon and germanium are examples of semiconductors

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10
Q

Charging by Conduction

A

A charged object (the rod) is placed in contact with another object (the sphere)

o Some electrons on the rod can move to the sphere

o When the rod is removed, the sphere is left with a charge

o The object being charged is always left with a charge having the same sign as the object doing the charging

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11
Q

Charging by Induction

A

When an object is connected to a conducting
wire or pipe buried in the earth, it is said to
be grounded

o A negatively charged rubber rod is brought
near an uncharged sphere

o The charges in the sphere are redistributed

o Some of the electrons in the sphere are repelled from the electrons in the rod

o A grounded conducting wire is connected to the sphere
oAllows some of the electrons to move from the sphere to the ground

o The wire to ground is removed, the sphere is left
with an excess of induced positive charge

o Charging by induction requires no contact with the
object inducing the charge

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12
Q

Charge Polarization

A

The charged object (on the
left) induces charge on the
surface of the insulator

o This realignment of charge on the surface of an insulator is known as polarization

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13
Q

Light: Animation

A

A charged comb attracts bits of paper due to polarization of the paper

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14
Q

Coulomb’s Law

A

F = (k |q1||q2|) / (r^2)

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15
Q

ke is called the Coulomb Constant

A

ke = 8.9875 x 109 N m2/C2

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16
Q

Remember that force is a ____ quantity

A

vector quantity

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17
Q

Electrostatic Force

A

o Both are inverse square laws

o The mathematical form of both laws is the same

o Masses replaced by charges

o Electrical forces can be either attractive or
repulsive

o Gravitational forces are always attractive

o Electrostatic force is stronger than the
gravitational force

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18
Q

Coulomb’s Law for Multiple
Charges

A

o The resultant force on any one charge
equals the vector sum of the forces exerted
by the other individual charges that are
present.

o Remember to add the forces as vectors

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19
Q

If q is positive

A

charge repels

20
Q

If q is negative

A

charge attracts

21
Q

Electrical Field

A

E (r on top) = ((F (I on top)) / (q (subscript o) = (K (subscript e) Q) / r^2

22
Q

Electrical Field SI units are

A

N / C

23
Q

The electric field is a _____ _____

A

vector quantity

24
Q

The direction of the field is defined to be the
direction of the electric force that would be
exerted on a _______

A

small positive test charge, qo,
placed at that point

25
Q

Direction of Electric Field

A

o The electric field produced by a
negative charge is directed toward
the charge

o A positive test charge would be
attracted to the negative source charge

o The electric field produced by a
positive charge is directed away from
the charge

o A positive test charge would be repelled
from the positive source charge

26
Q

Electric Field Lines

A

A convenient aid for visualizing electric field patterns

is to draw lines pointing in the direction of the field vector at any point

introduced by Michael Faraday

27
Q

The field lines are related to the field in the following manners

A

o The electric field vector, , is tangent to the
electric field lines at each point

o The number of lines per unit area through a
surface perpendicular to the lines is proportional to the strength of the electric field in a given region

28
Q

Electric Field Line Patterns

A

o Point charge

o The lines radiate equally in all
directions

o For a positive source charge, the
lines will radiate outward

o For a negative source
charge, the lines will point
inward

o The high density of
lines between the
charges indicates the
strong electric field in
this region

No two field lines can cross each other

29
Q

An electric dipole

A

consists of two equal
and opposite charges

30
Q

When no net motion of charge occurs within a
conductor, the conductor is said to be in ________ _______

A

electrostatic equilibrium

31
Q

An isolated conductor has the following properties

A

o The electric field is zero everywhere inside the conducting material

o Any excess charge on an isolated conductor resides entirely on its surface

o The electric field just outside a charged conductor is perpendicular to the conductor’s surface

o On an irregularly shaped conductor, the charge accumulates at locations where the radius of curvature of the surface is smallest (that is, at sharp points)

32
Q

QUICK QUIZ

A ping-pong ball covered with a conducting
graphite coating has a mass of 5.0 × 10−3 kg and a charge of 4.0 µC. What electric field directed upward will exactly balance the weight of the ball?
(g = 9.8 m/s2)

A
33
Q

Electric Flux

A

Field lines penetrating an area A perpendicular to the field

o The perpendicular to the area A is at an
angle θ to the field

34
Q

Electric Flux Equation

A

ΦE = E A cos θ

35
Q

The product of EA is

A

the flux, Φ

36
Q

When the area is constructed such that a
closed surface is formed, use the convention that flux lines passing into the interior of the volume are _________ and those passing out of the interior of the volume are _________

A

Pass into the interior of the volume are negative

Pass through the interior of the volume are positive

37
Q

Gauss’ Law

A

Gauss’ Law states that the electric flux through any closed surface is equal to the net charge Q inside the surface divided by εo

38
Q

Gauss’ Law Equation

A

ΦE = (Q inside)/(εo)

39
Q

εo is the

A

permittivity of free space and equals
8.85 x 10^-12 C^2/Nm2

40
Q

a Gaussian surface

A

The area in Φ is an imaginary surface, a Gaussian surface, it does not have to coincide with the surface of a physical object

41
Q

Total flex equation

A

Total Flex = (q1+q2)/(εo)

42
Q

Electric Field of a Charged Thin Spherical Shell

A

The calculation of the field outside the shell is identical to that of a point charge
E = (q/4pi(r^2)(εo) = ke (q/r^2)

The electric field inside the shell is zero

43
Q

Electric Field of a Nonconducting
Plane Sheet of Charge

A

Use a cylindrical
Gaussian surface

The flux through the
ends is EA, there is no
field through the
curved part of the
surface (A = 2A0)

The total charge inside
is Q = σA0

44
Q

Electric Field of a Nonconducting
Plane Sheet of Charge

Equation:

A

E = (σ)/(2εo)

45
Q

Parallel Plate Capacitor

A

o The device consists of plates of positive and negative charge

o The total electric field between the plates is given by

E = σ/εo

o The field outside the plates is zero

46
Q

QUICK QUIZ

A closed surface contains the following point
charges: 6 C, 4 C, –2 C, –4 C. The electric flux
coming out of the surface is:

A
47
Q
A

Physics 1202Q (12 decks)

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