Physics Exam 2

Resistors in combination: A resistor is made out of a long wire having a length L. Each end of the wire is attached to a terminal of a battery providing a constant voltage V0. A current I flows through the wire. If the wire were cut in half, making two wires of length L/2, and both wires were attached to the battery (the end of both wires attached to one terminal, and the other ends attached to the other terminal), what would be the total current flowing through the two wires?

4I

Batteries turn _________ into _________

Chemical to Electrical

Resistors in combination: In the circuit shown in the figure, four identical resistors labeled A to D are connected to a battery as shown. S1 and S2 are switches. Which of the following actions would result in the GREATEST amount of current through resistor A? a- then a switch to the upper (to B) and lower branch (to D) with a direct wire in the middle to C

Close both switches

Least Resistive to Most resistive

Conductors, Semi, Insulators

Resistivity: Perfect conductors would have ____ resistivity and perfect insulators would have ______ resistivity

Conductors- zero Insulators- infinite

To study a resistor and measure the current and voltage, how would the voltmeter/ammeter need to be placed

ammeter in series and voltmeter in parallel

Capacitance doubles, what happens to the energy?

becomes 1/2 as great

If a coil is rotated as shown, in a magnetic field pointing to the left, in what direction is the induced current?

ccw

the junction rule applies to what conservation of quality

charge

Circle rule with ijk- I at 12 o'clock, j at 4 o'clock, and k at 8 o'clock.

clockwise is positive, counterclockwise is negative

Dielectrics: An air-filled parallel-plate capacitor is connected to a battery and allowed to charge up. Now a slab of dielectric material is placed between the plates of the capacitor while the capacitor is still connected to the battery. After this is done, we find that

the charge on the capacitor had increased.

A charged particle moves through a region of space that has both a uniform elec field and a uniform mag field. for the particle to move at a constant velocity

the electric field and mag field must be in perpendicular directions

Capacitors in combination: When two or more capacitors are connected in parallel across a potential difference,

the potential difference across each capacitor is the same.

Compared to the potential energy of an electron before entering the source of emf, the pot energy of an electron after leaving the source is

the same

Capacitance (C)

Q/V where Q is the mag of charge and V is the pot diff between A and B. Measured in Farads (F)

Capacitors in combination: In the circuit shown in the figure, the capacitors are initially uncharged. The switch is first thrown to position A and kept there for a long time. It is then thrown to position B. Let the charges on the capacitors be Q1, Q2, and Q3 and the potential differences across them be V1, V2, and V3. Which of the following conditions must be true with the switch in position B? (C1 and C2 are in series and are parallel to C3)

Q1 + Q2 = Q3

Cap in parallel

Q=Q1+Q2+Q3... C=C1+C2+C3.... V is the same on all

Which of the following statements are true? -A battery does work on electric charges to bring them to a position of higher electric potential energy so that they can flow through a circuit to a lower potential energy. -The internal resistance of a battery decreases with decreasing temperature. -The potential difference between the terminals of a battery, when no current flows to an external circuit, is referred to as the terminal voltage. -A battery is a device that produces electricity by transforming chemical energy into electrical energy.

-A battery does work on electric charges to bring them to a position of higher electric potential energy so that they can flow through a circuit to a lower potential energy. -A battery is a device that produces electricity by transforming chemical energy into electrical energy.

Which of the following statements are true? -A capacitor consists of a single sheet of a conducting material placed in contact with an insulating material. -A capacitor is a device that stores electric potential energy and electric charge. -The electric field between the plates of a parallel-plate capacitor is uniform. -The capacitance of a capacitor depends upon its structure

-A capacitor is a device that stores electric potential energy and electric charge. -The electric field between the plates of a parallel-plate capacitor is uniform. -The capacitance of a capacitor depends upon its structure

Which of the following statements are true? -A material that obeys Ohm's law reasonably well is called an ohmic conductor or a linear conductor. -Semiconductors have resistivity values that are larger than those of insulators. -The resistance of a conductor is proportional to the resistivity of the material of which the conductor is composed. -The resistance of a conductor is proportional to the conductivity of the material of which the conductor is composed. -Good conductors of electricity have larger conductivity values than insulators.

-A material that obeys Ohm's law reasonably well is called an ohmic conductor or a linear conductor. -The resistance of a conductor is proportional to the resistivity of the material of which the conductor is composed. -Good conductors of electricity have larger conductivity values than insulators.

Which of the following statements are true? -An ammeter has a large internal resistance. -An ammeter must be placed in parallel with a resistor to measure the current through the resistor. -An ammeter is used to measure current. -A voltmeter has a small internal resistance. -A voltmeter must be placed in parallel with a resistor to measure the voltage across the resistor. -A voltmeter is used to measure voltage.

-An ammeter is used to measure current. -A voltmeter must be placed in parallel with a resistor to measure the voltage across the resistor. -A voltmeter is used to measure voltage.

Which of the following statements are true? -At any junction point in a circuit, the sum of all the currents entering the junction must equal the sum of all the currents leaving the junction. -Kirchhoff's junction rule is based on the conservation of energy. -The sum of the changes in potential around any closed loop of a circuit must equal zero. -Kirchhoff's loop rule is based on the conservation of charge.

-At any junction point in a circuit, the sum of all the currents entering the junction must equal the sum of all the currents leaving the junction. -The sum of the changes in potential around any closed loop of a circuit must equal zero.

Two cables of the same length are made of the same material, except that one cable has twice the diameter of the other cable. When the same potential difference is maintained across both cables, which of the following statements are true? (There may be more than one correct choice.)

-Both cables carry the same current density. -The electrons have the same drift velocity in both cables.

Which of the following statements are true? -By convention, the direction of a current is taken to be the direction of flow for negative charges. -In order to maintain a steady flow of current in a conductor, a steady force must be maintained on the mobile charges. -In a circuit, current is delivered by the positive terminal of a battery, and it is used up by the time it returns to the negative terminal of the battery. -When an electric field is applied to a conductor, the free electrons move only in the direction opposite the applied electric field. -Current is the total amount of charge that passes through a conductor's full cross section at any point per unit of time.

-In order to maintain a steady flow of current in a conductor, a steady force must be maintained on the mobile charges. -Current is the total amount of charge that passes through a conductor's full cross section at any point per unit of time

Consider three resistors with unequal resistances connected in parallel to a battery. Which of the following statements are true?

-The algebraic sum of the currents flowing through each of the three resistors is equal to the current supplied by the battery. -The equivalent resistance of the combination of resistors is less than the resistance of any one of the three resistors. -The voltage across each of the resistors is the same and is equal in magnitude to the voltage of the battery.

Consider two capacitors with unequal capacitance connected in series to a battery. Which of the following statements are true?

-The equivalent capacitance of the combination of the two capacitors is less than the capacitance of either of the capacitors. -The algebraic sum of the voltages across the two capacitors is equal to the voltage supplied by the battery -The charge stored on each of the capacitors is the same.

Consider three resistors with unequal resistances connected in series to a battery. Which of the following statements are true?

-The equivalent resistance of the combination of resistors is greater than the resistance of any one of the three resistors. -The algebraic sum of the voltages across the three resistors is equal to the voltage supplied by the battery. -The current flowing through each of the resistors is the same and is equal to the current supplied by the battery.

Consider two capacitors with unequal capacitance connected in parallel to a battery. Which of the following statements are true?

-The sum of the charge stored on each capacitor is equal to the charge supplied by the battery. -The equivalent capacitance of the combination is greater than the capacitance of either of the capacitors. -The voltage across each of the capacitors is the same.

When capacitance doubles, what happens to potential difference?

1/2

Res in parallel

1/R=1/R1+1/R2+1/R3... Voltage (V) is the same on each

Energy density: An ideal air-filled parallel-plate capacitor has round plates and carries a fixed amount of equal but opposite charge on its plates. All the geometric parameters of the capacitor (plate diameter and plate separation) are now DOUBLED. If the original energy density between the plates was u0, what is the new energy density?

16u0

A wire of resistivity ρ must be replaced in a circuit by a wire of the same material but 4 times as long. If, however, the resistance of the new wire is to be the same as the resistance of the original wire, the diameter of the new wire must be

2 times the diameter of the original wire.

Energy in capacitors: An ideal parallel-plate capacitor consists of a set of two parallel plates of area A separated by a very small distance d. When the capacitor plates carry charges +Q and -Q, the capacitor stores energy U0. If the separation between the plates is doubled, how much electrical energy is stored in the capacitor?

2U0

A circular loop of wire is placed next to a long wire, the current in the wire is increasing, whats happening in the loop?

A clockwise current

What must occur to keep a steady flow in a current?

A steady force must be present

Capacitor definition

Any two conductors separated by an insulator (or a vacuum). When charged, it means the two conductors have charges that are equal and opposite

Bulbs and their brightness

Bulbs in series draw less power and glow less than parallel bulbs

Two plates have an elec field in the middle with magnitude E, what happens to the elec field if the plates reach twice their original separation

E/2

As current flows through a uniform wire, the wire gets hotter because the electrons stop moving and therefore transform their lost kinetic energy into thermal energy in the wire.

False

Junction Rule vs Loop Rule

Kirchhoff's junction rule is based on the conservation of charge. Kirchhoff's loop rule is based on the conservation of energy.

Under what circumstance is the total mag flux through a closed surface positive?

Never

RC circuits: An RC circuit is connected across an ideal DC voltage source through an open switch. The switch is closed at time t = 0 s. Which of the following statements regarding the circuit are correct? (There may be more than one correct choice.)

Once the capacitor is essentially fully charged, there is no appreciable current in the circuit.

Ions having equal charges but masses of M and 2M are accelerated through the same potential difference and then enter a uniform magnetic field perpendicular to their path. If the heavier ions follow a circular arc of radius R, what is the radius of the arc followed by the lighter?

R/sqrt(2)

Res in series

R=R1+R2+R3... Current (I) is the same for each

Common Labels R= V= I=

R=resistivity, measured in Ohms V=Voltage/Pot diff, measured in V I=Current, measures in Amps (A)

What will be the resistance of this wire in terms of RR if it is stretched to three times its original length, assuming that the density and resistivity of the material do not change when the wire is stretched. (Hint: The amount of metal does not change, so stretching out the wire will affect its cross-sectional area.)

R′=9R

What happens when plates of equal size are separated?

Strength of field decreases Voltages is the same

Internal battery resistance: Two light bulbs, B1 and B2, are connected to a battery having appreciable internal resistance as shown in the figure. What happens to the brightness of bulb B1 when we close the switch S? (bulbs are in parallel, B1, battery, then B2 with the switch)

The brightness of B1 decreases permanently.

If the voltage across a circuit of constant resistance is doubled, how is the current in the circuit affected?

The current is doubled.

The figure shows a steady electric current passing through a wire with a narrow region. What happens to the drift velocity of the moving charges as they go from region A to region B and then to region C? Large-Small-Large

The drift velocity increases from A to B and decreases from B to C.

A dielectric material, such as Teflon®, is placed between the plates of a parallel-plate capacitor without altering the structure of the capacitor. The charge on the capacitor is held fixed. How is the electric field between the plates of the capacitor affected?

The electric field decreases because of the insertion of the Teflon®

Energy in capacitors: Equal but opposite charges Q are placed on the square plates of an air-filled parallel-plate capacitor. The plates are then pulled apart to twice their original separation, which is small compared to the dimensions of the plates. Which of the following statements about this capacitor are true? (There may be more than one correct choice.)

The energy stored in the capacitor has doubled.

The voltage applied across a given parallel-plate capacitor is doubled. How is the energy stored in the capacitor affected?

The energy stored in the capacitor quadruples its original value.

As additional resistors are connected in series to a constant voltage source, how is the power supplied by the source affected?

The power supplied by the source decreases.

As additional resistors are connected in parallel to a constant voltage source, how is the power supplied by the source affected?

The power supplied by the source increases.

Meters: A galvanometer G has an internal resistance rg. An AMMETER is constructed by incorporating the galvanometer and an additional resistance Rs. Which one of the figures below is the most appropriate circuit diagram for the ammeter?

The rg is in series to the G and the Rs is parallel to them both

The plates of a parallel-plate capacitor are maintained with a constant voltage by a battery as they are pulled apart. How is the strength of the electric field affected during this process?

The strength of the electric field decreases during this process.

A resistor, capacitor, and switch are all connected in series to an ideal battery of constant terminal voltage. Initially, the switch is open. What is the voltage across the resistor and the capacitor at the moment the switch is closed?

The voltage across the resistor is equal to the terminal voltage of the battery, and the voltage across the capacitor is zero.

A resistor and a capacitor are connected in series to an ideal battery of constant terminal voltage. When the system reaches its steady state, what is the voltage across the resistor and the capacitor?

The voltage across the resistor is zero, and the voltage across the capacitor is equal to the terminal voltage of the battery.

A dielectric material, such as Teflon®, is placed between the plates of a parallel-plate capacitor without altering the structure of the capacitor. The charge on the capacitor is held fixed. How is the voltage across the plates of the capacitor affected?

The voltage decreases because of the insertion of the Teflon®.

Energy in capacitors: An ideal air-filled parallel-plate capacitor has round plates and carries a fixed amount of equal but opposite charge on its plates. All the geometric parameters of the capacitor (plate diameter and plate separation) are now DOUBLED. If the original energy stored in the capacitor was U0, how much energy does it now store?

U0/2

Cap in series

V=V1+V2+V3.... 1/C=1/C1+1/C2+1/C3... Q is same on all

Each of the wires in the figures below carry the same current, either into or out of the page. In which case is the magnetic field at the center of the square greatest?

X X then o o

A flexible loop of wire is in a uniform mag field directed into the plane. the loop is pulled as shown reducing the area, the induced current flows

downward through the resistor and is proportional to B

A small circular ring of wire is inside a larger loop of wire that carries current I, if I increases, the current that flows in the small ring

is clockwise and is caused by self inductance

When electrons drift from a smaller wire into a larger wire, what happens to drift speed

it decreases

A long straight conductor passes through the center of a metal right, perp to plane. If the current in the conductor increases, is the current in the ring induced in the ring?

no current

A loop of wire is initially held above a short solenoid, where a constant ccw current passes through it. The loop of wire is steadily lowering, whats the direction of the current at the instant the loop is in the midpoint and still moving downwards

no current

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

If the current in a circuit is doubles, what happens to power

power is quadrupled

Meters: A galvanometer G has an internal resistance rg. A VOLTMETER is constructed by incorporating the galvanometer and an additional resistance Rs. Which one of the figures below is the most appropriate circuit diagram for the voltmeter?

they are all in series Rs, G, then rg

The long wire ab carries a 14 a current, the rectangular loop has long edges parallel to ab that carries a clockwise 5a current. What direction of the net mag force that the straight wire exerts on the loop?

upward

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

zero

A positive point charge is moving at constant velocity directly toward point P, the mag field that the point charge produces at point P is

zero