physics test 2

equation for resistance with regards to length and area

R=pl/A PLAR equation

Lenz's law only gives the ______ of induced current, not the ________ which depends on the resistance of the circuit

direction, magnitude

sin(0)

0

if flux is decreasing, induced emf or current is ______

positive

A positively charged particle moves in the positive z-direction. The magnetic force on the particle is in the positive y-direction. What can you conclude about the x-component of the magnetic field at the particle's position?

Bx>0 use RHR to see that the magnetic field must point to the right, so the x component is positive x

a charge moving at an angle to a magnetic field experiences a magnetic force with magnitude ______

F=qvBsin(angle) force is perpendicular to plane containing v and B

T/F If E is not zero at a point, then V cannot be zero at that point.

FALSE

self inductance

any circuit that carries a varying current has an emf induced in it by its own magnetic field

a point charge moving with constant velocity produces __________

both an E-field and B-field

example for PLANAR geometry for Gauss's Law

infinitely large slabs

A wire consists of two straight sections with a semicircular section between them. If current flows in the wire as shown, what is the direction of the magnetic field at P due to the current?

into the plane of the figure

A circular loop of wire carries a constant current. If the loop is placed in a region of uniform magnetic field, the net magnetic force on the loop

is zero because the forces cancel; there is a net torque, however

if flux is increasing, induced emf or current is _____

negative

The wire shown here is infinitely long and has a 90° bend. If current flows in the wire as shown, what is the direction of the magnetic field at P due to the current?

out of the plane of the figure

the momentum is responsible for ___________

radiation pressure

induced emf is proportional to the ________ of magnetic flux through the coil

rate of change

The RC circuit with the _______ time constant is the fastest to discharge

smallest

a point charge at rest produces a ______ but not a _________

static e field, b field

principle of superposition of magnetic field

the total magnetic field caused by several moving charges is the vector sum of the fields caused by individual charges

Gauss's Law For Magnetism

total magnetic flux through any closed surface equals zero

y x z

x

sin(90)

1

Z x X

Y

3 examples of CYLINDRICAL geometries for Gauss's Law

1. infinitely long lines 2. cylinder 3. concentric cylindrical shells

3 SPHERICAL geometries for Gauss's Law

1. point charge 2. solid sphere 3. concentric sphereical shells

Which of the following statements are true concerning electromagnetic radiation fields? 1. The electric and magnetic fields at any point are parallel to each other. 2. The magnetic field at any point is perpendicular to the direction of wave travel. 3. The electric and magnetic fields are phase-shifted 180° with respect to each other as they propagate through space. 4. The electric and magnetic fields are in phase with each other as they propagate through space. 5. The electric field at any point is perpendicular to the direction of wave travel.

2. The magnetic field at any point is perpendicular to the direction of wave travel. 4. The electric and magnetic fields are in phase with each other as they propagate through space. 5. The electric field at any point is perpendicular to the direction of wave travel.

range of visible light

380-750 nm

sinusoidal EM wave

E and B at any point are sinusoidal functions of time, and at any instant of time the spatial variation of the fields is also sinusoidal

time constant for RC circuit

T=RC

T/F As one moves away from a positive point charge both V and the magnitude of E decreases

TRUE

T/F If V depends only on the coordinate variables x and y, the Ez= 0

TRUE

T/F If V is constant at all points of a solid object, the E = 0 within the object.

TRUE

X x Y

Z

poynting vector

a vector that describes both the magnitude and direction of energy flow rate

plane wave

a wave in which at any instant the fields are uniform over any plane perpendicular to the direction of propagation

Ampere's law tells us that a time-varying _________ field acts as a source of a _______ field

electric, magnetic

E in the +x direction, B in the +y direction

propagation in +z direction

T/F EM waves transport energy and momentum

true

A resistor and an ideal inductor are connected in series to an ideal battery having a constant terminal voltage V 0. At the moment contact is made with the battery, the voltage across the resistor is

zero

3 symmetries of charge distribution for Gauss's Law

1. spherical geometry 2. cylindrical geometry 3. planar geometry

4 key properties of electromagnetic waves

1. the wave is transverse; both E-field and B-field are perpendicular to direction of propagation of wave; and direction of propagation of wave is E x B 2. there is a definite ratio between magnitudes of E-field and B-field; E=cB 3. the wave travels in vacuum with definite and unchanging speed; 3 x 10^8 m/s 4. unlike mechanical waves, which need particles of a medium such as air to transmit a wave, EM waves require no medium

Two long, straight wires are oriented perpendicular to the xy-plane. They carry currents of equal magnitude I in opposite directions as shown. At point P, the magnetic field due to these currents is in

positive x direction

A circular loop of wire carries a constant current. If the loop is placed in a region of uniform magnetic field, the net magnetic torque on the loop

tends to orient the loop so that its plane is perpendicular to the direction of the magnetic field.

A long, straight wire lies along the y-axis and carries current in the positive y-direction. A positive point charge moves along the x-axis in the positive x-direction. The magnetic force that the wire exerts on the point charge is in

positive y direction

electric field is equal to the rate of the change of _______

potential slope of potential vs time graph--> electric field

E in the -y direction, B in the +x direction

propagation in +z direction

E in the +y direction, B in the -z direction

propagation in -x direction

E in the +z direction, B in the -x direction

propagation in -y direction

the variable k is called the _____ of the wave

wavenumber

T/F: Gauss' law is valid only for symmetric charge distributions in electrostatic equilibrium, such as spheres and cylinders.

FALSE

the variable w is called the _____ of the wave

angular frequency

4 key characteristics of magnetic force on a moving charge

1. magnitude of force is proportional to the magnitude of the charge (i.e. if a 1C charge and a 2C charge move through a B-field with same velocity, the force on the 2C charge will be twice as much as the force on the 1C charge) 2. magnitude of the force is proportional to the magnitude of the field (i.e. if we double magnitude of field by using 2 bar magnets instead of 1, the force doubles) 3. magnetic force depends on particle's velocity (charged particle at rest experiences no magnetic force) 4. the magnetic force is always perpendicular to both the magnetic field and the velocity (if v and B are parallel or antiparallel, force is zero)

Y x X

-Z

z x y

-x

X x Z

-y

Which of the following statements are true? 1. A time-varying magnetic field will produce an electric field. 2. Time-varying electric and magnetic fields can propagate through space only if there is no matter in their path. 3. A time-varying electric field will produce a magnetic field. 4. Electric and magnetic fields can be treated independently only if they vary in time.

1. A time-varying magnetic field will produce an electric field. 3. A time-varying electric field will produce a magnetic field.

Which of the following statements are true? Check all that apply. 1. Electromagnetic waves can exert pressure on an object. 2. Electromagnetic waves transport linear momentum. 3. Electromagnetic waves transport mass from one region of space to another. 4. Electromagnetic waves transport energy from one region of space to another.

1. Electromagnetic waves can exert pressure on an object. 2. Electromagnetic waves transport linear momentum. 4. Electromagnetic waves transport energy from one region of space to another.

Which of the following statements are true concerning electromagnetic induction? Check all that apply. 1. It is possible to induce a current in a closed loop of wire by change the orientation of a magnetic field enclosed by the wire. 2. It is possible to induce a current in a closed loop of wire without the aid of a power supply or battery. 3. It is possible to induce a current in a closed loop of wire remaining at rest and located in a uniform magnetic field. 4. It is possible to induce a current in a closed loop of wire located in a uniform magnetic field by either increasing or decreasing the area enclosed by the loop. 5 .It is possible to induce a current in a closed loop of wire by changing the strength of a magnetic field enclosed by the wire.

1. It is possible to induce a current in a closed loop of wire by change the orientation of a magnetic field enclosed by the wire. 2. It is possible to induce a current in a closed loop of wire without the aid of a power supply or battery. 4. It is possible to induce a current in a closed loop of wire located in a uniform magnetic field by either increasing or decreasing the area enclosed by the loop. 5 .It is possible to induce a current in a closed loop of wire by changing the strength of a magnetic field enclosed by the wire.

Consider a magnetic force acting on an electric charge in a uniform magnetic field. Which of the following statements are true? 1. The direction of the magnetic force acting on a moving electric charge in a magnetic field is perpendicular to the direction of motion. 2. An electric charge moving perpendicular to a magnetic field experiences a magnetic force. 3. A magnetic force is exerted on a stationary electric charge in a uniform magnetic field. 4. An electric charge moving parallel to a magnetic field experiences a magnetic force. 5. The direction of the magnetic force acting on a moving charge in a magnetic field is perpendicular to the direction of the magnetic field. 6. A magnetic force is exerted on an electric charge moving through a uniform magnetic field.

1. The direction of the magnetic force acting on a moving electric charge in a magnetic field is perpendicular to the direction of motion. 2. An electric charge moving perpendicular to a magnetic field experiences a magnetic force. 5. The direction of the magnetic force acting on a moving charge in a magnetic field is perpendicular to the direction of the magnetic field. 6. A magnetic force is exerted on an electric charge moving through a uniform magnetic field.

Consider the electromagnetic field produced at a given distance from a light source. Which of the following statements are true? Check all that apply. 1. The intensity of the wave is proportional to the speed of light. 2. The intensity of the wave is inversely proportional to the square of the fields. 3. The intensity of the wave is inversely proportional to the speed of light. 4. The intensity of the wave is proportional to the square of the fields.

1. The intensity of the wave is proportional to the speed of light. 4. The intensity of the wave is proportional to the square of the fields.

Which of the following statements are true? 1. The south poles of two bar magnets will repel each other. 2. The north poles of two bar magnets will attract each other. 3. Earth's geographic south pole is also a magnetic south pole. 4. The north pole of a bar magnet will attract the south pole of another bar magnet. 5. Earth's geographic north pole is actually a magnetic south pole. 6. Scientists have evidence that single isolated magnetic poles, called magnetic monopoles, exist.

1. The south poles of two bar magnets will repel each other. 4. The north pole of a bar magnet will attract the south pole of another bar magnet. 5. Earth's geographic north pole is actually a magnetic south pole.

A resistor, an inductor, and a switch are all connected in series to an ideal battery of constant terminal voltage. Suppose at first the switch is open, and then, at some initial time t = 0, it is closed. Which of the following statements are true? 1. The steady-state value of the current depends on the resistance of the resistor. 2. At the instant the switch is closed, the current begins to increase at a rate that depends upon the value of the inductance of the inductor. 3. At the instant the switch is closed, the current reaches its steady-state value. 4. The steady-state value of the current depends on the inductance of the inductor

1. The steady-state value of the current depends on the resistance of the resistor. 2. At the instant the switch is closed, the current begins to increase at a rate that depends upon the value of the inductance of the inductor

right hand rule for direction of magnetic force on a positive charge moving in a magnetic field

1. place the v and B vectors tail to tail 2. imagine turning v toward B in the v-B plane 3. the force acts along a line perpendicular to the v-B plane; curl the fingers of your right hand around the line in the same direction you rotated v; your thumb now points in the direction the force acts

Which of the following statements are true concerning the creation of magnetic fields? 1. A single stationary electric charge creates a magnetic field at all points in the surrounding region. 2. An electric current in a conductor creates a magnetic field at all points in the surrounding region. 3. A permanent magnet creates a magnetic field at all points in the surrounding region. 4. A moving electric charge creates a magnetic field at all points in the surrounding region. 5. A distribution of electric charges at rest creates a magnetic field at all points in the surrounding region.

2. An electric current in a conductor creates a magnetic field at all points in the surrounding region. 3. A permanent magnet creates a magnetic field at all points in the surrounding region. 4. A moving electric charge creates a magnetic field at all points in the surrounding region.

Which of the following statements are true concerning electromagnetic waves in a vacuum? 1. Electromagnetic waves traveling in a vacuum are longitudinal waves. 2. When electromagnetic waves travel in vacuum, there is a definite, constant ratio between the magnitudes of the electric and magnetic fields. 3. Electromagnetic waves travel in a vacuum with a definite and unchanging speed. 4. Electromagnetic waves can travel in a vacuum only because a medium prohibits the forward propagation of the electric and magnetic fields.

2. When electromagnetic waves travel in vacuum, there is a definite, constant ratio between the magnitudes of the electric and magnetic fields. 3. Electromagnetic waves travel in a vacuum with a definite and unchanging speed.

Which of the following statements are true for magnetic field lines? 1. Magnetic field lines point in the direction of the magnetic force acting on a charge. 2. Magnetic field lines are close together in regions of space where the magnitude of the magnetic field is weak, and they are father apart in regions where it is strong. 3. At every point in space, the magnetic field vector at that point is tangent to the magnetic field line through that point. 4. Unlike electric field lines, magnetic field lines are continuous. 5. Magnetic field lines can never intersect.

3. At every point in space, the magnetic field vector at that point is tangent to the magnetic field line through that point. 4. Unlike electric field lines, magnetic field lines are continuous. 5. Magnetic field lines can never intersect.

Two long parallel wires are placed side by side on a horizontal table. The wires carry equal currents in the same direction. Which of the following statements are true? 1. The magnetic force between the two wires is repulsive. 2. The magnetic field is a maximum at a point midway between the two wires. 3. The magnetic force between the two wires is attractive. 4. The magnetic field at a point midway between the two wires is zero.

3. The magnetic force between the two wires is attractive. 4. The magnetic field at a point midway between the two wires is zero.

Which of the following statements about inductors are correct? 1. When an inductor and a resistor are connected in series with a DC battery, the current in the circuit is reduced to zero in one time constant. 2. When an inductor and a resistor are connected in series with a DC battery, the current in the circuit is zero after a very long time. 3. Inductors store energy by building up charge. 4. An inductor always resists any change in the current through it. 5. When it is connected in a circuit, an inductor always resists having current flow through it.

4. An inductor always resists any change in the current through it.

A circular loop of wire lies flat on a level table top in a region where the magnetic field vector points straight upward. The magnetic field suddenly vanishes. As viewed from above, in what direction does the induced current flow in the loop of wire? No current is induced in the loop of wire. An induced current flows clockwise in the loop of wire. The direction of the induced current cannot be determined from the given information. An induced current flows counterclockwise in the loop of wire.

An induced current flows counterclockwise in the loop of wire.

The magnitude of the magnetic field at a certain distance from a long, straight conductor is represented by B. What is the magnitude of the magnetic field at twice the distance from the conductor? At twice the distance, the magnitude of the field is 2B. At twice the distance, the magnitude of the field is 4B. At twice the distance, the magnitude of the field remains equal to B. At twice the distance, the magnitude of the field is B/2. At twice the distance, the magnitude of the field is B/4.

At twice the distance, the magnitude of the field is B/2. B= uI/ 2pir so if R is increased by 2, B is decreased by 2

A positively charged particle moves in the positive z-direction. The magnetic force on the particle is in the positive y-direction. What can you conclude about the y-component of the magnetic field at the particle's position?

By=0 use RHR to see that all of the B-field is in +x direction

Identical capacitors A and B are fully charged by the same battery. Capacitor A is disconnected from the battery while capacitor B remains connected to it. Identical dielectric slabs are inserted between the plates of the capacitors. Which of the following is true? A. The final capacitance of A is greater than that of B. B. The final charge is the same for both capacitors. C. The final stored energy is greater for B. D. The final voltage is the same for both capacitors

C -A has constant Q, and B has constant V. If capacitance goes up for both, then potential energy will decrease in A and increase in B

T/F lightning is more likely to strike a tall tree than a short one because the potential difference between the thundercloud and the tall tree is larger

FALSE All trees have the same potential as ground; but a tall tree is closer to the cloud, therefore higher E-field magnitude

a charge moving perpendicular to a magnetic field experiences a __________ magnetic force with magnitude______

MAXMIMAL, F=qvb angle is 90, and sin of 90 is 1

if the flux is constant, there is ________ induced emf

NO

A circular loop of wire lies flat on a level table top. A bar magnet is held stationary above the circular loop with its north pole point downward. As viewed from above, in what direction does the induced current flow in the loop of wire? No current is induced in the loop of wire. An induced current flows clockwise in the loop of wire. The direction of the induced current cannot be determined from the given information. An induced current flows counterclockwise in the loop of wire.

No current is induced in the loop of wire because held stationary

T/F The electric flux passing through a Gaussian surface depends only on the amount of charge enclosed by that surface, not on the size or shape of the surface.

TRUE

T/F There is no charge on the walls of an EMPTY cavity within a conductor, regardless of what charges might be on the outer surface of the conductor

TRUE

T/F: A collection of positive charges with total charge Q is deposited on a conducting cube and the charge is in static equilibrium. The potential at one corner of the cube is the same as the potential at the center of the cube. (All potentials are measured relative to infinity.)

TRUE

T/F: If a Gaussian surface is completely inside a solid conductor in electrostatic equilibrium, the electric field must always be zero at all points on that surface.

TRUE

T/F: The surface of a conductor in electrostatic equilibrium is an equipotential surface.

TRUE

T/F magnetic flux is a scalar

TRUE if B is uniform over a plane surface with total area A, then B(perpendicular) and the angle are the same at all points on the surface

T/F: E-field and potential outside the sphere (r > R) with a uniform charge distribution is the same as those produced by a point charge of Q at the center of the sphere. This equivalence is true for either a conducting or non-conducing sphere.

TRUE!

T/F: The total charge in a closed system cannot be changed by any means

TRUE! closed system, conservation of charge

T/F: X and Y are two uncharged metal spheres on insulating stands, and are in contact with each other. A positively charged rod R is brought close to X as shown in Figure (a). Sphere Y is now moved away from X, while X is is held close to R, as shown in Figure (b). The final charge states are X is negative and Y is positive.

TRUE; charging my induction

unit for magnetic field

Tesla (T) Gauss (G) = 10^-4 T

A charged particle enters into a uniform magnetic field such that its velocity vector is perpendicular to the magnetic field vector. Ignoring the particle's weight, what type of path will the particle follow? The charged particle will follow a circular path. The charged particle will follow a spiral path. The charged particle will follow a parabolic path. The charged particle will follow a straight-line path.

The charged particle will follow a circular path.

Consider an electromagnetic wave propagating through a region of empty space. How is the energy density of the wave partitioned between the electric and magnetic fields? The energy density of an electromagnetic wave is entirely in the magnetic field. The energy density of an electromagnetic wave is 25% in the magnetic field and 75% in the electric field. The energy density of an electromagnetic wave is 25% in the electric field and 75% in the magnetic field. The energy density of an electromagnetic wave is equally divided between the magnetic and electric fields. The energy density of an electromagnetic wave is entirely in the electric field.

The energy density of an electromagnetic wave is equally divided between the magnetic and electric fields.

What is the velocity of all electromagnetic waves in a vacuum? The velocity of electromagnetic waves depends upon their amplitude. The velocity of electromagnetic waves is nearly equal to 3 × 108 m/s. The velocity of electromagnetic waves depends upon their wavelength. Electromagnetic waves do not propagate forward; hence, their velocity is zero. The velocity of electromagnetic waves depends upon their frequency.

The velocity of electromagnetic waves is nearly equal to 3 × 108 m/s.

equations for potential energy in capacitors

U=1/2 QV= I/2 CV^2= Q^2/ 2C

A resistor and an ideal inductor are connected in series to an ideal battery having a constant terminal voltage V 0. At the moment contact is made with the battery, the voltage across the inductor is

V0

unit of magnetic flux

Weber (Wb)

A positive point charge is moving at constant velocity directly toward point P. The magnetic field that the point charge produces at point P

ZERO because the r vector and velocity are in same direction, so there is no cross product

in order for a point charge to produce EM waves, the charge must __________

accelerate

in EVERY situation in which EM waves are radiated, the source is _________

accelerated charges

Lenz's Law

any induction effect tends to oppose the change that caused it ex. an induced current creates a magnetic field through the loop, and the right-hand-rule shows that this field is opposite in direction to the increasing field produced by the electromagnet

A positively charged particle moves in the positive z-direction. The magnetic force on the particle is in the positive y-direction. What can you conclude about the z-component of the magnetic field at the particle's position?

can't conclude anything

momentum is a property of the ________ and is not associated with the _______ of a moving particle

field, mass

Faraday's law tells us that a time-varying _________ field acts as a source of a ________ field

magnetic, electric

A particle with a positive charge moves in the xz-plane as shown. The magnetic field is in the positive z-direction. The magnetic force on the particle is in

negative Y direction

The fact that the magnetic field generates a force perpendicular to the instantaneous velocity of the particle has implications for the work that the field does on the particle. As a consequence, if only the magnetic field acts on the particle, its kinetic energy will ____________.

remain constant

transverse waves

satisfies Maxwell's first and second equations, the electric and magnetic fields must be perpendicular to the direction of propagation

time constant for LR circuit

t=L/R current has risen to about 63% of final value

A charged particle moves through a region of space that has both a uniform electric field and a uniform magnetic field. In order for the particle to move through this region at a constant velocity,

the electric and magnetic fields must point in perpendicular directions.

A beam of electrons (which have negative charge) is coming straight toward you. You place a magnet as shown directly above the beam. The magnetic field from the magnet points straight down. Which way will the electron beam deflect?

to the left use RHR and point thumb out in direction of beam, point fingers down in direction of B-field. Palm is facing right, but it is negatively charged, so force is to the left

a charge moving parallel to a magnetic field experiences ______ magnetic force

zero v and B are parallel

what is the magnetic flux through any closed surface?

zero because any flux that enters a closed surface must also leave it