When Vo=0m/s, + charges accelerate from regions of high potential to low potential, - charges will accelerate from low potential to high potential, and work must be done on - charges to make them go in the opposite direction.

The potential created by a point charge q at any distance r from the charge is:

V=ke(q/r)

The point of zero electric potential is taken to be at an infinite distance from the charge.

Difference between the electric field and electric potential.

The electric field is proportional to 1/r^2 The electric potential is proportional to 1/r

The potential energy for a 2-particle system

The work required to bring q2 from infinity to P without acceleration. PE = q2V1= ke((q1*q2)/r)

What happens to PE and Wo when the charges have the same sign?

PE is + and Wo is + when force the 2 charges to get nearer one another.

What happens to PE and Wo when the charges have the dif. sign?

PE is - and Wo is + when force the 2 charges to get far from one another.

Problem-Solving w/ Electric Potential (Point Charges)

- Draw a diagram of all charges. - Note the point of interest P. - Calculate the r from each charge to P. - Use V = keq/r - V is + if +q and - if the charge is -q.

What are the caracteristics of a charged conductor in electrostatic eq.?

All points on the surface W = 0, VA = VB. E = 0 inside the conductor. The E is outside the conductor, and is perpendicular to the surface.

The e- Volt

The kinetic energy that an e-/p+ gains when accelerated through 1 V.

Equipotential surface

The surface on which all points are at the same potential. W = 0, VA = VB. And the E outside the surface is perpendicular to the surface.

Capacitance

Ratio of the magnitude of the charge on either plate to the magnitude of the potential difference between the plates.

Unit for capacitance.

Farads(F)

How does a capacitor Wo?

When connected to the battery, charge is pulled off one plate and transferred to the other plate. The transfer/flow stops when DifVcap = DifVbattery when they reach their maximum charge

Capacitance, Potential dif. and total charge in a Parallel-Plate Capacitor.

- C=Epsilon(A/d) & Ceq = C1 + C2 + … - Epsilon: permitivity of free space 8,85x10^-12 (C^2)/(N.m^2) - The plates have the same potential difference. Dif V=DifV1=Dif V2=... - The total charge, Q, is equal to the sum of the charges on the capacitors. Q = Q1 + Q2

Electric Field in a Parallel-Plate Capacitor

Uniform near the center Nonuniform near the edges

Circuit

Collection of objects usually with a source of electrical energy connected to elements that convert it in to other forms.

Capacitors in Series

- C=Epsilon(A/d) & (Ceq/1) = (1/C1)+(1/C2)+... - The potential differences add up to the battery voltage. Dif V=DifV1+Dif V2+... - The magnitude of the charge must be the same on all the plates. Q = Q1= Q2

Energy Stored in a Capacitor

Energy stored = ½ Q ΔV IN THE IMAGE V=ΔV

Dielectric Strength?

The maximum electric field can be produced in the dielectric before it breaks down and begins to conduct.

Atomic Description of Dielectrics

The field produces an induced polarization in the dielectric material and the capacitance increases.

Dielectric:

Insulating material or a very poor conductor of electric current.

What does R=R0(1+a(T-T0)) state?

That resistance varies according temperature.

Power?

The amount of power delivered to a device.

How can you calc. the Power delivered to a resistor?

P=I^2R=dif.V^2/R

Kilowatt-hour:

Amount of energy converted in one hr by a device supplied w/power at a rate of 1kW.

Sources of emf?

Battery or generator, increases the electric potential energy of charges in an electric circuit.

Dif. between batteries and generators?

Batteries convert chemical energy into electrical potential energy, and generators convert mechanical energy into electrical potential energy.

How the terminal voltage dif.V of a battery is calc?

Dif.V=E-Ir E=emf of the battery r=internal resistance of the battery (small)

Resistors in series:

- Req=R1+R2+...+Rn - Dif.V=Dif.V1+Dif.V2= IR1+IR2=IReq

Resistors in parallel:

- Req=1/(1/R1)+(1/R2) - I= I1+I2=(dif.V/R1)+(dif.V/R2)= dif.V/Req

What have a Simple RC circuit?

A battery, a resistor, and a capacitor in series. Or a resistor and a capacitor.

How a charge on the capacitor on a RC cicuit is calculated ?

Q=Q(1-e^(-t/RC)) or q=Qe^(-t/RC) when the RC circuit has only a resistor and a capacitor.

Formula for resistivity of a conductor with a length l and a cross-area A:

R=p(l/A) p= electrical resistivity

SI of resistance

Ohms=V/A

Reistance?

Ohms law Dif.V=RI

With what formula is the current related to the motion of the charge carriers?

I=nqvA n=#of mobile charge carriers per vol. v=drift speed. A= cross area of the conductor

SI Current unit

Ampere=C/s

Current:

Time rate flow of charge through a surface.

How to know the sign of the epsylon=dif.V in a source of Electro Motif Force(battery)?

If the direction of the EMF is the same in which you are transversing (from - to +), the dif.V should be a positive= rise in the IR. If the direction of the EMF is the opposite in which you are transversing (from + to -), the dif.V should be negative= drop in the IR.

How to know the sign of the IR=dif.V in a resistor?

If the direction of I(current) is the same in which you are transversing, the IR should be negative=drop in the IR. If the direction of I(current) is the opposite in which you are transversing, the IR should be positive= rise in the IR.

What does p=p0(1+a(T-T0)) state?

That resistivity varies according temperature.

When does the Kirchhoff's Rules (Radiation) are used?

When the resistors are connected and the circuits formed cannot be reduced to a single eq resistor.

Explain the 2 Kirchhoff's Rules

- Junction Rule(conservation of charge): The sum of the currents entering a juction= sum of the currents leaving that junction. I1=I2+I3 -Loop rule (conservation of energy): The sum of the V dif of all the elements around any closed circuit loop=0.

How to apply Kirchhoff's Rules:

- Assign symbols & directions to the currents I: If the direction of a current is incorrect, the ans=- but the correct magnitude. - Use junction rule. - Choose CCW or CW direction to transverse the loops: Record V rises & drops. - Loop rule. - Solve a single variable.

How AC electric motor works?

Revelsal of the current ocures naturally.

How do we assume happen to the solenoid B?

Inside is uniform and outside is 0.

What is the direction of a Charged particle in a magnetic field with a velocity perpendicular to the field and a force directed to the center of the circular path?

The magnetic force= centripetal acceleration, changing the direction of the velocity of the particle. F= q v B= (mv^2)/ r

How was the electron discover/proved?

Cyclotron equation: r=mv/qB

What happen if the particle's velocity isn't perpendicular to the field?

The path is a spiral.

Julie effect?

A current will start going in the filament and because of the dissipation of the energy/resistance= light.

Right Hand Rule for the direction of the Field of a long Straight wire.

Point the thumb in the direction of the current and curl the fingers in the direction of the field.

How to calc. the magnitude of the field, of the distance r from the wire carrying a current I :

B= (mue)I/2(pie)r mue=4(pie)x10^-7 Tm/A - In a close circular path.

What is mue?

The permittivity of free space.

Ampère's Circular Law

(sigma BII)(dif L)= (mue) I Bll (sigma dif L)= (mue) I - sigma dif L= Arbitrary perimeter of the close path

How can you obtain the Force Between 2 Parallel Conductors?

The force on wire 1 is due to the I in wire 1 and the B by wire 2. F/L= ((mue)I1 I2)/2 pie d

How could you obtain the field B2 at wire 1?

F1= (B2) L (I1)

Is the F attractive or repulsive when 2 parallel wires have their I in oposite directions?

The F is repulsive, and attractive when the wires have same direction.

How can you enhance the strength of a B?

Forming a wire into a loop, with a B at the center pointing up/down and at the sides perfect circles. Resembling the field lines of a magnet bar.

How do you calc. the Magnetic fields of a Current Loop?

B= mue I/2R- at the center of the loop B=N mue I/2R- at the loop

Solenoid?

It's a wire bend as a coil/ electromagnet because it carries a current.

How do you calc. the Magnetic fields inside a solenoid?

B= mue n I n= N/L

What happen when a charged particle is moving through a magnetic field?

A magnetic force acts on it (Loren's force), with a max when the particle moves perpendicular to the magnetic field lines and 0 when moves parallel to the field lines.

How is magnetism linked to electricity?

Magnetic Fields affect the motion of charges, charges in motion produce magnetic fields, and changing magnetic fields can create electric fields.

Poles:

Located at the ends of the object (N and S) where the objects are most attracted. Like poles attract each other and unlike repeal each other. But cannot be isolated, in charges yes. When you break a magnet you would have a south and a north.

How can an unmagnetized piece of iron can be magnetized?

Stroking it with a magnet, like an uncharged object is charged by conduction. Because magnetism can be inducted.

Difference between soft and hard magnetic materials:

Soft are easily magnetized, but lose their magnetism easily and Hard are diff. to magnetize and lose their magnetism.

Sources of Magnetic Fields:

Region surrounding a moving charge (includes a magnetic & electric field) & a magnetized magnetic material.

Properties of Magnetic Fields:

1° Vector quantity. 2° Symbol: B. 3° Directed to the north. 4° Magnetic field lines show how the field would look like (direction, loops)

Dif. between the magnetic and electric field lines?

Magnetic are close loops trying to reach each other and electrical dipole are forming open loops.

Earth Margnetic Field.

The north is the south, the south is the north.

How DC electric motor works?

W/ a single loop connected to the power of the direct current, connect to brushes to change the direction of the current giving the loop the force to keep rotating. The loop is inside of a magnet (electro motive force or a magnetic field). As the loop becomes perpendicular to the magnetic field and the T=0, inertia carries the loop forward and the brushes cross the gaps in the ring= current reverse direction.

How to calc. the magnitude of the magnetic force?

B=F/(q v sin(theta)) theta is the angle between the v and B

Magnetic field unit:

The tesla(T) or Wb/m^2 or 10^4gauss=1T

Right hand rule to the magnetic field.

F is perpendicular to both V and B. Use the right hand to positive charge and left to negative charges.

Why do we have a force on a Current Carrying Conductor(wire)?

The current is a collection of many charged particles in motion, creating a magnetic field. The direction of the force given by the right-hand rule. The magnetic force is exerted on each moving charge.

The total magnetic force on a current-carrign conductor?

Sum of all the magnetic forces on every charge producing the current. F= B q (length) sin(theta)

Rules of a Torque on a current loop:

T= B I A N sin(theta) theta= angle between IAN and B. With a max when theta=90° & 0 when theta=0/parallel to the plane of the loop. - Any shape of loop.

Solenoid

Conductor that is on loops.

Magnetic moment:

Mue= IAN - The vector points perpendicular to the loop's plain. SO... T= mue B sin (theta)

General Physics 2-Exam 2

Capacitance, resitance and magnetism

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