Physics 107
Connecting a wire between the plates establishes
-which causes electrons to flow from the negative plate (which has an excess of electrons) toward the positive plate.establishes an electric field in the wire, -The potential difference creates the electric field that drives the current in the wire -Eventually the plates will be completely discharged, meaning no more potential difference, no more field, and no more current.
Identical metal spheres are initially charged as shown. Spheres P and Q are touched together and then separated. Then spheres Q and R are touched together and separated. Afterward the charge on sphere R is
0 nC
what is a battery
A battery is a source of voltage difference. The current that flows through a wire connecting the battery terminals is a consequence of the voltage difference
what is a junction
A junction is a point where a wire branches.
Parallel-Plate Capacitor: Summary
A parallel-plate capacitor creates a uniform electric field E. V = 0 at the negative plate, and V = ΔVC at the positive plate x is the distance from the negative plate. The potential difference between any two points is ∆V = E∆x The potential at a point x is
what is a parallel plate cap
A parallel-plate capacitor is a capacitor where both electrodes (i.e. plates) are thin, flat, and parallel to each other.
Columbus law only applies to point charges, what are point charges
A point charge is an idealized material object with charge and mass but with no size or extension. For practical purposes, two charged objects can be modeled as point charges if they are much smaller than the separation between them
how is the potential difference created
A potential difference is created by separating positive charge from negative charge.
what are equipotential surfaces
A three-dimensional view showing equipotential surfaces. These are mathematical surfaces, not physical surfaces, that have the same value of V at every point. The equipotential surfaces of a capacitor are planes parallel to the capacitor plates. The capacitor plates themselves are also equipotential surfaces.
What does insulator do
An insulator does not have free charges and cannot carry a current.
the electric field is zero at all points inside a conductor in electrostatic equilibrium.
Any excess charge inside a conductor must lie at its surface. The electric field right at the surface of a charged conductor is perpendicular to the surface.
the charge of the capacitor is equal to the
C times delta Vc=potential difference between two electrodes
what is the capacitance of a parallel plate capactior formula
C=EoA/d
exp 6
Charge a plastic rod by rubbing it with wool. Touch a neutral metal sphere with the rubbed area of the rod. The metal sphere then repels a charged, hanging plastic rod. The metal sphere appears to have acquired a charge of the same sign as the plastic rod.
what is discharging
Discharging is removing a charge from an object, which you can do by touching it.
what is the electric field strength inside the capacitor is
E= ∆VC/d
the electric field inside pp c is
E=Q/e0A e0=permittivity constant= 1/4πK=8.85×10−12 C2/N⋅m2
Charged glass and plastic rods hang by threads. An object attracts the glass rod. If this object is then held near the plastic rod, it will
Either A or B. There's not enough information to tell The object could have same charge as plastic, which would repel the plastic rod. Or it could be neutral and attract both charged rods
what is the electrostatic constant
K
* What does more current mean
More current means a brighter bulb
Charge is represented by the symbol q
The SI unit of charge is the coulomb (C), named for French scientist Charles Coulomb, one of many scientists investigating electricity in the late 18th century.
What is Kirchhoff's junction law.
The basic conservation statement, that the sum of the currents into a junction equals the sum of the currents leaving
What are charge carriers
The charges that move in a current are called In metal-they are called electrons
what is important to remember
The current at point B is exactly equal to the current at point A. The current leaving a lightbulb is exactly the same as the current entering the lightbulb
Why does glass acquire one charge after rubbing with silk, and plastic a different charge after rubbing with wool?
The fact that rubbing induces a charge is called the triboelectric effect.
what does the hand do
The hand does work W, transferring energy into the system of charges.
What does current mean
The motion of charges through a material
A capacitor's inital E-field polarizes the dielectric; the dielectric creates an electric field opposite the capacitor's field
The two fields add to give a net field in the same direction as the applied field, but smaller. Thus the electric field between the capacitor plates is smaller with a dielectric.
what happens to the voltage in a parallel plate capacitor
The voltage increases linearly from the negative plate (x = 0) to the positive plate at x = d.
Consider two objects A and B. Object A has a net charge while B is uncharged. Based on this information, it must be true that
There's not enough information to tell.
whatisnotchangedinalightbulb
Thus, the number of electrons is not changed by the lightbulb. The lightbulb cannot store electrons, or it would become increasingly negative until its repulsive force would stop the flow of new electrons and the bulb would go out.
what is an electric dipole .
Two equal but opposite charges with a separation between them
To find the voltage at a point in space,
We calculate the electric potential energy of a charge q at a point. Then we can solve for the voltage.
what is the long range repulsive force
a force requiring no contact
cooper wire carries
a larger current than a iron wire with same dimensions
If a certain amount of positive charge appears somewhere
an equal amount of negative charge must appear elsewhere so that the net charge doesn't change.
what is a dielectric
an insulator placed between the plates of a capacitor.
when is an object charged
an object is charged if it has an unequal number of electrons and protons.
what are insulators
are materials in which charge is immobile
what does a battery do
battery creates a fixed potential difference using chemical processes to create internal charge separation
The induced charge on an insulator will create a uniform electric field, like in a parallel-plate capacitor
but one that is directed opposite to the applied electric field.
how is the electric potential created
by source charges and is present at every point
what is the constant of proportionality C
capacitance
what do The capacitors on this circuit board store
charge and electrical potential energy
what are currents
charges in motion, so we define current as the rate, in coulombs per second, at which charge moves through a wire.
What is current measured in
coulombs/second, which we define as an ampere A. 1 amp=1 C/s Household currents are typically ~ 1 A or 1 amp
what is the current the flow of
current is the flow of positive charge -In metals, it is typically negative charges (electrons) flowing - but negative charges moving left is effectively the same as positive charge moving right
In a capacitor, the electric field strength E and the potential difference ΔVC are directly proportional to the charge on the electrodesdirectly proportional to the charge on the electrodes
directly proportional to the charge on the electrodes
a neutral object contains
equal amounts of positive and negative charge
what is the SI unit
farad=1 C/V
the electric field points away
from a postivie charge
The current direction in a wire is
from higher potential to lower potential, or in the direction of the electric field.
the force on negative charge is
in opposite direction of electric field
the force on a postivie charge is what
in the direction of the electric field
what is capacitor
is formed by two conductors (called electrodes or plates)
what is electrostatic equilibrium
is the condition in which the charges on an isolated conductor are in static equilibrium with the charges at rest.
what is charge polarization
is the slight separation of the positive and negative charges in a neutral object when a charged object is brought near.
if postivie to negative is in the left direction
it is to the left
short thick wire long thin w
larger current ire smaller current
what does a capacitor with a LARGE capacitance hold
more charge for a given potential difference than one with a small cap
electrons and protons have charges
of opposite signs and equal magnitude
what is the dielectric constant k
of the material determines the factor by which the capacitance is increased:
SI unit of resistance is
ohm
What is Ohm's Law do
relates the current in this bulb to the battery's voltage and the bulb's resistance to the flow of charge.
like charges exert what
repulsive forces on each otherht
Since the force increases closer to the source charge
the change in potential increases as well.
what is electrostatic equilibrium
the charges on an isolated conductor are in static equilibrium with the charges at rest.
When a dielectric is inserted
-the electric field between the plates decreases, which implies the potential difference decreases as well. The charge remains the same. -The capacitance C = Q/ΔVC increases. -The presence of a dielectric results in an increased capacitance.
How re electric field lines drawn
-the electric field vector are tangent to the electric field lines -the electric field is stronger where the electric field vectors are longer and where the eletric field lines are longer
what is the force on a postivie and negative charge of an electric ield
-the force on the + charge is in the direction of the electric field
electron volt is a unit of enery which equals
1 eV = 1.60 × 10-19 J
What does one electron volt mean
1 electron volt is the kinetic energy gained by an electron (or proton) as it accelerates through a potential difference of 1 volt.
A neutral object is not something with no charge
A neutral object contains equal amounts of positive and negative charge.
Metal spheres 1 and 2 are touching. Both are initially neutral. The charged rod is brought near. The charged rod is then removed. The spheres are separated. Afterward, the charges on the sphere are:
Q1 is 0 and Q2 is 0
for a parallel place capacitor
Q=eoA times delta Vc/d
what is discharging
Removing charge from an object,
The discharge of a capacitor lights two identical bulbs. Compare the brightness of the two bulbs.
They are Equally Bright reason Current is conserved, so any current that goes through bulb 1 must go through bulb 2 as well—the currents in the two bulbs are equal.
what does a capacitor have
the two electrodes have equal and opposite charges
what are the two factors that determine resistance
the voltage difference and the properties of the wire. -First, the current is proportional the the voltage difference. -Adding a second battery doubles the potential difference, which doubles the electric field and therefore the current (approximately). Increasing the length of the wire connecting a battery decreases the current, while increasing the thickness of the wire increases the current
As the capacitor discharges, if the wire is very thin in places, like the filament of a lightbulb
the wire gets hot enough to glow
what are the electric potential and electric field
they are two different perspectives (or two different mathematical representations) of how source charges alter the space around them
what are conducters
those materials through or along which charge easily moves metal
in an electric field where does the field point
toward + charge away from - charge
what is the the electric field between the two plates is
uniform
we find that the field inside a parallel-plate capacitor is the same— so it sis a
uniform electric field
The motion of the electrons will cease unless what
unless you continue pushing by maintaining an electric field.
what does the potential on The potential at a given point depends on
where we choose V to be zero.
if you have two charges and you need to find the potneital
you need to use V=kq/r +
For a junction, the law of conservation requires
ΣIin = ΣIout
The electric field in a parallel-plate capacitor with plate area A and charge Q is given by:
ϵ0, pronounced "epsilon zero" or "epsilon naught," called the permittivity constant. Its value is related to the electrostatic constant as
what is the potential of a point charge formula The electric potential energy Uelec of two charges q and q' separated by a distance r:
(𝐾𝑞𝑞^′)/𝑟
q can be
+ or - like charges point away opposite charges point toward
In a parallel-plate capacitor, the initial separation of charges creates
, the initial separation of charges creates a potential difference between the plates.
Inside a parallel-plate capacitor how are the components
- the horizontal components of the individual fields cancel. -The vertical components add to give an electric field vector pointing from the positive plate to the negative plat
what is a capacitor
-A capacitor is the arrangement of two electrodes that are closely spaced and charged equally but oppositely -An electrode is another name for a conducting plate.
what are three important things about the field
-The electric field, a vector, exists at every point in space. Electric field diagrams will show a sample of the vectors -If the probe charge q is positive, the electric field vector points in the same direction as the force on the charge; if negative, the electric field vector points opposite the force. -electric field does not depend on magnitude of charge used to probe the field Thus the electric field defined in Equation 20.3 is independent of the charge q that probes the fiel
what are the three things to note about pp c
-The field depends on the charge-to-area ratio Q/A, which is often called the charge density. If the charges are packed more closely, the fields will be larger. -In the following discussions, we will assume that the separation of the plates to be small compared to their size. If this is true, the spacing between the plates does not affect the electric field. -The shape of the electrodes is not relevant as long as the electrodes are close together.
A battery with no current in it has a potential difference -
-equal to its emf. With a current, the battery's potential difference is slightly less than its emf. -The battery itself has a small internal resistance We'll overlook this small difference and assume ΔVbat = E
Why a neutral metal object is attracted to a charged object.
-neutral sphere has equal amounts of postivie and negative charge -negative charge is attracted to postivie rod. this leaves behind a postivie charge on the other side of the sphere -the negative charge on the sphere is close to the rod so it is attracted to the rod -the net forces is TOWARD the rod -the postivie charge on the sphere is far from the rod, so it is weakly repelled
what does a charge escalator do
-sustains the current in a wire by providing a continuously renewed supply of charges at the positive terminal -Once a charge reaches the positive terminal, it can flow downhill through the wire until it reaches the negative terminal again.
what is important to remember about a capacitor
A capacitor stores separated charges, but has no means to do the separation. A charged capacitor has a potential difference but not an emf.
what is the magnitude
If two charged particles having charges q1 and q2 are a distance r apart, the particles exert forces on each other of magnitude
Dielectrics and Capacitors
An insulator consists of vast numbers of atoms. When an insulator is placed in an electric field, each atom polarizes. Polarization occurs because the atom's negative electron cloud and positive nucleus shift very slightly in opposite directions in response to the applied electric field An induced positive charge builds up on one surface of the insulator, and an induced negative charge builds up on the other surface
A rod attracts a positively charged hanging ball. The rod is
Either B or C.
Charge model, part I
Frictional forces, such as rubbing, add something called charge to an object or remove it from the object. The process itself is called charging. More vigorous rubbing produces a larger quantity of charge. There are two kinds of charge, positive and negative. Two objects with like charge (positive/positive or negative/negative) exert repulsive forces on each other. Two objects with opposite charge (positive/negative) exert attractive forces on each other. We call these electric forces. The force between two charged objects is a long-range force. The magnitude of the force increases as the quantity of charge increases and decreases as the distance between the charges increases. Neutral objects have an equal mixture of positive and negative charge. The rubbing process charges the objects by transferring charge (usually negative) from one to the other. The objects acquire equal but opposite charges. Charge is conserved: It cannot be created or destroyed.
Start with a neutral, uncharged hanging plastic rod and a piece of wool. Rub the plastic rod with the wool, then hold the wool close to the rod. The rod is attracted to the wool.
From Experiment 3 we know that the plastic rod has a negative charge. Because the wool attracts the rod, the wool must have a positive charge.
what is the definition of current formula
I=delta q/delta t
Metal spheres 1 and 2 are touching. Both are initially neutral. The charged rod is brought near. The spheres are separated. The charged rod is then removed. Afterward, the charges on the sphere are:
Q1 is - and Q2 is + net charge is obtained if contact is broken while the spheres are polarized. this is charging by induction
How is an electric potential created?
Only potential differences matter. The value of the potential at a single point is not physical (just like potential energy, the potential can be set to zero anywhere). A potential difference is created by separating positive charge from negative charge. A potential difference exists wherever there is a non-zero Electric field
exp 7
Place two metal spheres close together with a plastic rod connecting them. Charge a second plastic rod, by rubbing, and touch it to one of the metal spheres. Afterward, the metal sphere that was touched repels a charged, hanging plastic rod. The other metal sphere does not.
he magnitude of the force between point charges is given by Coulomb's law:
Show the directions of the forces—repulsive for like charges, attractive for opposite charges—on the visual overview. >>>Draw the lengths of your force vectors according to Coulomb's law: A particle with a greater charge, or one that is closer, will lead to a longer force vector. When possible, do graphical vector addition on the visual overview. While not exact, it tells you the type of answer you should expect. Write each force vector in terms of its x- and y-components, then add the components to find the net force. Use the visual overview to determine which components are positive and which are negative.
what is the avg The average strength of an electric field component over a distance Δx where the potential changes by ΔV is
The average strength of an electric field component over a distance Δx where the potential changes by ΔV is Equipotentials are more widely spaced when the field is weaker, closer when the field is stronger
how can the The capacitance can be changed (e.g. by inserting a dielectric) under one of two conditions
The capacitor is still connected to the battery. In this case, the battery forces the capacitor to maintain a steady potential difference, i.e. ∆VC = constant ⇒ Q changes The capacitor is disconnected from the battery. In this case, the charge has nowhere to go, so it cannot change. Q = constant ⇒ ∆VC changes
The electric field at a point is perpendicular to the equipotential surface at that point.
The electric field points in the direction of decreasing potential
where does the electric field point
The electric field points in the direction of decreasing potential.
what is the difference between electric potential and electrical potential energy
The electric potential (or voltage) V at a point is the potential for creating an electric potential energy if a charge were to be placed at that point.
what is true about a voltage of a sphere
The voltage outside a charged sphere is the same as the voltage outside a point charge
what is an electron volt
The electron volt is the kinetic energy gained by an electron (or proton) as it accelerates through a potential difference of 1 volt. 1 electron volt = 1 eV = 1.60 × 10-19 J
what is a complete circuit
The flow of charge in a continuous loop is called a complete circuit.
what is there in an electric dipole though
There is a net torque on a dipole in a uniform electric field, which causes it to rotate. The electric dipole moment is a vector pointing from the negative to the positive charge of a dipole.
imp
The polarization force between a charged object and a neutral one is always attractive.
what is emf
The potential difference established by a device, such as a battery, that can actively separate charge is called
what is the electric field
The space around a charge is altered
what is the symbol for emf
The symbol for emf is and its units are volts.
What is the voltage of a battery
The voltage of a battery is the difference in electric potential between its two terminals.
How do you charge a capacitor
To "charge" a capacitor, we need to move charge from one electrode to the other. The simplest way to do this is to use a source of potential difference such as a battery. A battery uses its internal chemistry to maintain a fixed potential difference between its terminals.
what is a parallel plate capcitator
Two conducting plates, called electrodes, are face-to-face with a narrow gap between them. One electrode has total charge +Q and the other has total charge −Q
what is the relationship between electric potential and electrical potential energy
Uele=qV
The electric potential in a uniform field is:
Uelec = W = qEx
sphere formula
V=RVo/r -It is common to charge a metal object, such as a sphere, "to" a certain potential, for instance using a battery -The potential decreases inversely with distance from center.
What is the electric potential 1.0 cm from a 1.0 nC charge?
V=kq/r
A proton or electron that accelerates through a potential difference of V
gains V eV of kinetic energy A proton or electron the decelerates through a potential difference of V volts loses V eV of kinetic energy.
Resistance R is
a measure of how hard it is to push charges through a wire. A large resistance implies that it is hard to move charges through the wire.
the field vectors point toward
a negative charge
what is the electric potential (or voltage)
a point is the potential for creating an electric potential energy if a charge were to be placed at that point.
what is A charge q is repelled by
a stationary source charge . A external force, in this case the hand, must push on the charge q in order to move it closer to the source charges.
what is the dipole moment
a vector that points from the negative to the p ostivie charge
what happens in a constant electric field
an electron's average motion will be opposite the field. The motion is the electron's drift velocity.
conducters
are those materials through or along which charge easily moves.
What are insulators?
as those materials on or in which charges remain immobile. glass, plastic
opposite charges exert what
attractive forces on each otsidf
what does capacitance depend on
the shape, size, and spacing of the two electrodes.
what does a parallel plate capacitor do
creates a uniform electric field E.
+ and -
do not represent indivdual changes
equal number of signs are repesented
equl number of signs
as q' which is negative approaches q it will
gain KE, lose PE
few things to note about the field in a parallel-plate capacitor:
he field depends on the charge-to-area ratio Q/A, which is often called the charge density. If the charges are packed more closely, the field will be larger. Our analysis requires that the separation of the plates be small compared to their size. If this is true, the spacing between the plates does not affect the electric field, and this spacing does not appear in Equation 20.7. Although Figure 20.29 shows circular electrodes, the shape of the electrodes—circular or square or any other shape—is not relevant as long as the electrodes are very close together.
why does the polarization force arise
in insulators arises because the charges in a neutral object are slightly separated, not because the objects are oppositely charged.
the strength of the force is greater for rods that have been rubbed ,
more vigoursly
what is the current I due to
motion of charges in electric field
in the rubbing process
no charge was created or destoryed
what occurs in an electric dipole a uniform electric field experiences
no net force.
In a conductor in electrostatic equilibrium
none of the charges are moving.
Collisions between the electrons and the atoms of the metal does what
slow them down, transforming the electron's kinetic energy into thermal energy, making the metal warmer.
what do capacitors do
store charge, making them invaluable in electronics
The strength of the force is greater for rods
that have been rubbed more vigorously.
What is a voltmeter?
the basic instrument for measuring potential differences, always has two inputs. It measures the potential difference, not the potential at a point
what is C0
the capacitance without a dielectric present.
what is at the pointed end
the charges are closer together and the electric field is strongest at the pointed end
What happens when the capacitor discharges
the connecting wire gets warmer
what is the law of conservation of current
the current is the same at all points in a current carryin wire
the electric field is what in a parallel capacitator
the electric field at every point is the same in both strength and direction. which is called an uniform electric field
what does the electric potential tell us
the electric potential tells us how a source would provide q with potential energy.
how are electrons in a wire felt
the energy is dissipated by atomic-level friction as the electrons move through the wire, making the wire hotter until it glows.
What happens when we When we apply an electric field to a metal,
the field exerts a force on the electrons and they begin to accelerate
what is the electric field model tell us
the field is the agent that exerts an electric force on a particle with charge q.
what is electric force
the force between charged objects
if two rods are held farther from each other
the force between them decrease
If the two rods are held farther from each other
the force between them decreases.
what is fundamental charge
the magnitude of the charge of an electron or a proton. The fundamental charge e has been measured to have the value e=1.60×10−19 C
if Delta K is negative
the particle slows down
If Delta K is postivie then what
the particle speeds up as it moves from higher to lower potential
What happens if if we connect the two capacitor plates of a parallel-plate capacitor with a metal wire,
the plates become neutral. The capacitor has been discharged.
In the case where q and q¢ are opposite charges
the potential energy of the charges is negative.
what is the The potential difference ΔVC between the two capacitor plates is
∆VC = V+ - V− = Ed
In terms of electric potential V the potential energy is
𝑈_elec=𝑞𝑉
what is the The voltage at position x inside a capacitor is
𝑉=𝐸𝑥=(Δ𝑉_C)/𝑑 𝑥
The electric potential (voltage) can be written
𝑉=𝑈_𝑒𝑙𝑒𝑐/𝑞
