Physics 2-Final

What fundamental fact underlies the operation of essentially all electric motors?

A current-carrying conductor placed perpendicular to a magnetic field will experience a force.

Fig. 28-1 above shows two long wires carrying equal currents I1 and I2 flowing in opposite directions. Which of the arrows labeled A to D correctly represents the direction of the magnetic field due to the wires at a point located at an equal distance d from each wire?

B

A proton, moving north, enters a magnetic field of a certain strength. Because of this field the proton curves downward. What is the direction of the magnetic field?

towards the east

The average energy dissipated in an inductor is

zero.

The force on a current-carrying wire in a magnetic field is the strongest when

the current is perpendicular to the field lines.

A capacitor, initially charged, and an inductor form an LC circuit. When the electric current in the circuit is equal to zero how much energy is stored on each device?

Inductor: zero energy. Capacitor: maximum energy

Fig. 28-3 shows three long, parallel current-carrying wires. The magnitudes of the currents are equal and their directions are indicated in the figure. Which of the arrows drawn near the wire carrying current 1 correctly indicates the direction of the magnetic force acting on that wire?

A

The figure below shows 2 bar magnets of the same size and the same strength. Which of the arrows labeled A to D correctly represents the direction of the magnetic field at a point located at the common origin of the arrows? (That point is at an equal distance from the two magnets.)

A

Faraday's law of induction and Lenz's law are actually the same law stated differently.

False

If two identical wires carrying a certain current in the same direction are placed parallel to each other, they will experience a force of repulsion.

False

The field near a long straight wire carrying a current is inversely proportional to the current flowing through the wire.

False

The magnetic field near a current carrying wire is directly proportional to the distance from the wire.

False

The magnitude of the magnetic field inside a solenoid is inversely proportional to the current flowing through the solenoid.

False

If the current increases in a solenoid, the induced emf acts to

If the current increases in a solenoid, the induced emf acts to

In a velocity selector having electric field E and magnetic field B, the velocity selected for positively charged particles is v = E/B. The formula is the same for a negatively charged particles.

True

Magnetic field lines can never cross one another.

True

Part A According to Lenz's Law, the direction of the induced current in a conducting loop of wire is that which tends to oppose the change that produces it.

True

The field outside a solenoid behaves like that of a bar magnet.

True

The magnetic field unlike the electric field is continuous.

True

The negative sign in the Faraday's equation for electromagnetic induction is related to the direction of the induced emf.

True

There is no induced emf in a wire that is moving parallel to a magnetic field if the wire is moving in the direction of the magnetic field.

True

An electric current produces

a magnetic field.

Three particles travel through a region of space where the magnetic field is out of the page, as shown in Fig. 27-4. The electric charge of each of the three particles is, respectively,

1 is negative, 2 is neutral, and 3 is positive.

Fig. 27-3 shows a small positive charge q moving toward a long current-carrying wire. Which of the arrows labeled A to D correctly represents the direction of the magnetic force applied on the charge?

C

Fig. 28-2 shows four different sets of wires that cross each other without actually touching. The magnitude of the current is the same in all four cases, and the directions of current flow are as indicated. For which configuration will the magnetic field at the center of the square formed by the wires be equal to zero?

C

The figure below shows 3 bar magnets of equal sizes and equal strengths. At which of the points labeled A to E is the magnetic field approximately equal to zero? (Points B and C are at equal distances from the magnets.)

C

A constant magnetic flux through a closed loop of wire induces an emf in that loop.

False

An emf is induced in a wire by keeping a stationary magnet near the wire.

False

Cutting a bar magnet near its north end results in a smaller mostly north pole magnet and a larger mostly south pole magnet.

False

A rectangular coil lies flat on a horizontal surface. A bar magnet is held above the center of the coil with its north pole pointing down. What is the direction of the induced current in the coil?

There is no current in the coil.

A changing magnetic field can produce an electric current.

True

A changing magnetic flux through a closed loop of wire induces an emf in that loop.

True

A charged particle traveling opposite to a magnetic field does not experience a magnetic force.

True

A constant magnetic field can be used to produce an electric current.

True

A current carrying wire placed in a magnetic field perpendicular to the wire experiences a maximum force.

True

An emf is induced in a wire by changing the current in that wire.

True

An emf is induced in a wire by moving the wire near a magnet.

True

If the minus sign were not in Faraday's law it would lead to a violation of the law of conservation of energy.

True

In using Ampere's law, the integral must be evaluated

around a closed path.

If the south pole of one bar magnet is brought near the north pole of a second bar magnet, the two magnets will

attract

A horizontal wire carries a current straight toward you. From your point of view, the magnetic field caused by this current

circles the wire in a counter-clockwise direction.

What is the direction of the induced current in the loop when the loop is above the solenoid, moving downward?

clockwise

A rectangular coil lies flat on a horizontal surface. A bar magnet is held above the center of the coil with its north pole pointing down. If the magnet is dropped from this position what is the direction of the induced current in the coil?

counterclockwise

What is the direction of the induced current when the loop is below the solenoid and moving downward?

counterclockwise

A long, straight wire carrying a current is placed along the y-axis. If the direction of the current is in the +y direction, what is the direction of the magnetic field due to this wire?

counterclockwise, around the y-axis

A charged particle is injected into a uniform magnetic field such that its velocity vector is perpendicular to the magnetic field vector. Ignoring the particle's weight, the particle will

follow a circular path.

A transformer is a device used to

increase or decrease an ac voltage.

A vertical wire carries a current straight up in a region where the magnetic field vector points due north. What is the direction of the resulting force on this current?

west

A square loop of wire carrying a current in a clockwise direction lies in the plane of the paper. The magnetic field inside the loop is directed

into the paper everywhere.

In a transformer, the power input

is equal to the power output.

Part A Two long parallel wires placed side-by-side on a horizontal table carry identical current straight toward you. From your point of view, the magnetic field at the point exactly between the two wires

is zero.

The wire in Fig. 29-2 carries a current I that is increasing with time at a constant rate. The induced emf in each of the loops is such that

loop A has clockwise emf, loop B has no induced emf, and loop C has counterclockwise emf.

The magnetic permeability of a ferromagnetic material is

much greater than μo.

What is the direction of the induced current at the instant that the loop is at the midpoint of the solenoid and still moving downward?

no current

According to Lenz's law, the direction of an induced current in a conductor will be that which tends to produce which of the following effects?

oppose the effect which produces it

The direction of the force on a current-carrying wire in a magnetic field is described by which of the following?

perpendicular to both the current and the magnetic field

Two long parallel wires placed side-by-side on a horizontal table carry identical size currents in opposite directions. The wire on your right carries current toward you, and the wire on your left carries current away from you. From your point of view, the magnetic field at the point exactly midway between the two wires

points down

A current carrying loop of wire lies flat on a table top. When viewed from above, the current moves around the loop in a counterclockwise sense. What is the direction of the magnetic field caused by this current, outside the loop? The magnetic field

points straight down.

A vertical wire carries a current straight down. To the east of this wire, the magnetic field points

south

If the number of turns on the secondary coil of a transformer are less than those on the primary, the result is a

step-down transformer.

Magnetic flux depends upon

the area involved. the orientation of the area with respect to the field. the magnetic field.

The force on a current-carrying wire in a magnetic field is equal to zero when

the current is parallel to the field lines.

The earth's northern magnetic pole acts like

the south pole of a magnet.

Two long parallel wires are placed side-by-side on a horizontal table. If the wires carry current in the same direction,

the wires attract each other.

Electric power is transmitted over long distances at high voltage because

there is less power lost.

An electron, moving south, enters a magnetic field of certain strength. Because of this field the electron curves upward. What is the direction of the magnetic field?

towards the west

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

zero.