# Physics 115 Mastering Physics

## Unlock all answers in this set

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In the video, the temperature of the gas inside the fire piston increased because
Work was done on the gas when the plunger was depressed.
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Which physical law underlies the first law of thermodynamics?
conservation of energy
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When the quantity Q is greater than zero, __________ is added to the system.
heat
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When the quantity W in the first law is greater than zero, it refers to the __________.
work done on the system
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The quantity ΔEth in the first law of thermodynamics is the change in the __________ of the system.
thermal energy
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If heat is added to a system (Q>0) and no change in thermal energy of the system occurs (ΔEth=0), then the system must do __________ work on the outside world.
positive
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The second law of thermodynamics imposes what limit on the efficiency of a heat engine?
A heat engine must deposit some energy into a cold reservoir
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A refrigerator is an example of a __________.
heat pump
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If we assume a typical efficiency for the body, as quoted in the video, how much energy input would it take to climb a ladder, increasing your body's potential energy by 5,000 J?
20,000 J
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A typical efficiency of the human body is about _____.
25%
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A machine uses 1000 J of electric energy to raise a heavy mass, increasing its potential energy by 300 J. What is the efficiency of this process?
30%
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The entropy of an isolated system _________.
either increases or remains constant
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In the video, we use the atomic model to describe pressure as resulting from
The force from the collision of gas molecules with the walls of their container
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An atom's atomic mass number is the number of its ______.
protons + neutrons
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The three different gas-law processes described in this video are
Constant volume, constant pressure, and constant temperature.
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A sample of nitrogen gas is inside a sealed container. The container is slowly compressed, while the temperature is kept constant. This is a(n) ________ process
isothermal
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A sample of nitrogen gas is in a sealed container with a constant volume. Heat is added to the gas. The pressure __________
increases
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When the temperature of an ideal gas is increased, which of the following also increases?
the average kinetic energy of the gas atoms
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Which type of heat transfer can happen through empty space?
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Heat is added to each block at the same constant rate until it reaches a temperature of 500 K. Which of the following statements is true?
The iron takes less time than the aluminum to reach the final temperature.
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When the two materials have reached thermal equilibrium, the block of aluminum is cut in half and equal quantities of heat are added to the iron block and to each portion of the aluminum block. Which of the following statements is true?
The blocks remain in thermal equilibrium.
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Due to concerns about the toxic properties of mercury, many thermometers are made with other liquids. Consider draining the mercury from the above thermometer and replacing it with another, such as alcohol. Alcohol has a coefficient of volume expansion 5.6 times greater than that of mercury. The amount of alcohol is adjusted such that when placed in ice water, the thermometer accurately records 0∘C . No other changes are made to the thermometer. When the alcohol thermometer is placed in 20∘C water, what temperature will the thermometer record?
greater than 20∘C
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When the alcohol thermometer is placed in a −10∘C substance, what temperature will the thermometer record?
less than −10∘C
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If you want to design a thermometer with the same spacing between temperature markings as a mercury thermometer, how must the diameter of the inner hollow cylinder of the stem of the alcohol thermometer compare to that of the mercury thermometer? Assume that the bulb has a much larger volume than the stem.
√(5.6) times wider
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Which of the following pairs of terms are used to describe what is happening in the video?
phase change, calorimetry
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When steam condenses into water, __________
heat is given off by the water
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The defining equation for calorimetry is __________
Q1 + Q2 = 0
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To understand the heat conduction formula and the variables in it. Conduction—the flow of heat from a hotter object to a cooler object or from a hotter region to a cooler region of the same object—is the most common mechanism of heat transfer. The formula governing this is H=ΔQΔt=kA(TH−TCL), where H is known as the heat current. This formula applies to ________________.
any object of cross-sectional area A, length L, and thermal conductivity k
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The quantity ΔQ/Δt is the rate of heat transfer from the hot to the cold end of the rod
true
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The quantity ΔQ/Δt is the rate of heat added to the hot end of the rod to maintain its temperature.
true
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The quantity ΔQ/Δt is the rate of heat removed from the cold end of the rod to maintain its temperature.
true
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The quantity ΔQ/Δt is the total amount of heat transferred from the hot to the cold end of the rod
false
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In the SI system of units, what are the units of the quantity ΔQ/Δt
watts
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The thermal conductivity of copper _________ than that of stainless steel.
is greater
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The pot needs to distribute energy evenly over the bottom to cook the food evenly, so it needs to have _______ conductivity. The handle thermal conductivity_________ , so it won't get so hot and burn the hands.
high, is smaller
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What is the SI unit of pressure?
the pascal
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The pressure inside a latex balloon is nearly the same as the pressure outside. If you let a helium balloon go, and if, as it rises, it stays at a constant temperature, the volume of the balloon will
increase
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Salt water has a greater density than fresh water. Given this, there are objects that will
float in salt water but sink in fresh water
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The buoyant force on an object submerged in a liquid depends on __________
the density of the liquid
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When a viscous fluid flows in a tube, its velocity is __________
greatest at the center of the tube
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If you place a charged object next to an uncharged object that is a conductor,
There is an attractive force between the two objects
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There is a force between two charged objects. To decrease the magnitude of the force, we can
Move the objects farther from each other or reduce the charge on either of them.
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Coulomb's law describes __________
the force between two point charges
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A neutral object __________.
has no net charge
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A negatively charged rod is brought near a neutral metal sphere. Which of the following is true?
There is an attractive force between the rod and sphere.
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A small metal ball is given a negative charge, then brought near (i.e., within about 1/10 the length of the rod) to end A of the rod (Figure 1) . What happens to end A of the rod when the ball approaches it closely this first time?
it is strongly attracted
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After a great many contacts with the charged ball, how is the charge on the rod arranged (when the charged ball is far away)?
There is a negative charge spread evenly on both ends
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How does end A of the rod react when the charged ball approaches it after a great many previous contacts with end A? Assume that the phrase "a great many" means that the total charge on the rod dominates any charge movement induced by the near presence of the charged ball.
It is strongly repelled
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How does end B of the rod react when the charged ball approaches it after a great many previous contacts with end A?
it is strongly repelled.
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A glass marble is rubbed against a piece of silk. As a result the piece of fabric acquires extra electrons. What happens to the glass marble?
The marble has lost the same number of electrons acquired by the piece of silk The marble acquires a positive charge and attracts the piece of silk.
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Two glass marbles (1 and 2), each supported by a nylon thread, are rubbed against a piece of silk and then are placed near a third glass marble (3), also supported by a similar thread. Assuming that marble 3 has not been in contact with the piece of fabric, which of the following statements best describes the situation when the three marbles are brought together? To keep things simple in this Tutorial, we will ignore the effects of polarization and just focus on the overall charge of each object.
Marbles 1 and 2 repel each other, but no interaction occurs with marble 3.
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What is the final charge on each sphere if C is touched to B, removed, and then touched to A?
3q/8, -q/4, 3q/8
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Starting again from the initial conditions, what is the charge on each sphere if C is touched to A, removed, and then touched to B?
q/2, 0, 0
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The field inside a charged parallel-plate capacitor is __________
uniform
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The electric field direction is defined by the direction of the force felt by
A positive charge
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The electric field inside a metallic conductor is _____
zero
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For the charge distribution provided, indicate the region (A to E) along the horizontal axis where a point exists at which the net electric field is zero. (Figure 1) If no such region exists on the horizontal axis choose the last option (nowhere).
C
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For the charge distribution provided, indicate the region (A to E) along the horizontal axis where a point exists at which the net electric field is zero. (Figure 2) If no such region exists on the horizontal axis choose the last option (nowhere).
B
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For the charge distribution provided, indicate the region (A to E) along the horizontal axis where a point exists at which the net electric field is zero. (Figure 3) If no such region exists on the horizontal axis choose the last option (nowhere).
nowhere
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For the charge distribution provided, indicate the region (A to E) along the horizontal axis where a point exists at which the net electric field is zero. (Figure 4)
A
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A small object A, electrically charged, creates an electric field. At a point P located 0.250 m directly north of A, the field has a value of 40.0 N/C directed to the south. What is the charge of object A?
−2.78×10−10 C
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If a second object B with the same charge as A is placed at 0.250 m south of A (so that objects A and B and point P follow a straight line), what is the magnitude of the total electric field produced by the two objects at P?
50.0 N/C
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Consider the following configuration of fixed, uniformly charged spheres in (Figure 1) : a blue sphere fixed at the origin with positive charge q, a red sphere fixed at the point (d1,0) with unknown charge qred, and a yellow sphere fixed at the point (d2cos(θ),−d2sin(θ)) with unknown charge qyellow. The net electric force on the blue sphere has a magnitude F and is directed in the − y direction. What is the sign of the charge on the yellow sphere?
negative
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What is the sign of the charge on the red sphere?
positive
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Suppose that the magnitude of the charge on the yellow sphere is determined to be 2q. Calculate the charge qred on the red sphere. Express your answer in terms of q, d1, d2, and θ.
2qcos(theta) (d1/d2)^2
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As in the video, we apply a charge +Q to the half-shell that carries the electroscope. This time, we also apply a charge -Q to the other half-shell. When we bring the two halves together, we observe that the electroscope discharges, just as in the video. What does the electroscope needle do when you separate the two half-shells again?
It does not deflect at all.
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What are the units of potential difference?
V
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In other units, 1 V is equal to
1 J/C
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Rank in order, from highest to lowest, the electric potentials at points a, b, and c. Rank from highest to lowest. To rank items as equivalent, overlap them.
a=c, b
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What would be the potential at B if a 40 nC charge were moved from A to B?
V = 150V
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Mustang Sally just finished restoring her 1965 Ford Mustang car. To save money, she did not get a new battery. When she tries to start the car, she discovers that the battery is dead (an insufficient or zero voltage difference across the battery terminals) and so she will need a jump start. Here is how she accomplishes the jump start: She connects a red jumper cable (wire) from the positive terminal of the dead battery to the positive terminal of a fully functional new battery. She connects one end of a black jumper cable to the negative terminal of the new battery. She then connects the other end of the black jumper cable to the negative terminal of the dead battery. The new battery (now in a parallel with the dead battery) is now part of the circuit and the car can be jump started. The car starter motor is effectively drawing current from the new battery. After the car with the dead battery is running, the cables can be disconnected in the reverse order that they were connected. While unhooking the jumper cables, the positive and negative cables almost touch and a spark jumps between the ends of the cables. This spark is caused by the movement of electrons through the air between the battery terminals. In what direction are the electrons traveling during the spark?
The electrons are traveling from the negative to the positive terminal.
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There is a 12 V potential difference between the positive and negative ends of the jumper cables, which are a short distance apart. An electron at the negative end ready to jump to the positive end has a certain amount of potential energy. On what quantities does this electrical potential energy depend?
only the potential difference and the charge
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Assume that two of the electrons at the negative terminal have attached themselves to a nearby neutral atom. There is now a negative ion with a charge −2e at this terminal. What are the electric potential and electric potential energy of the negative ion relative to the electron?
The electric potential is the same and the electric potential energy is twice as much.
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What is the electric potential energy of an electron at the negative end of the cable, relative to the positive end of the cable? In other words, assume that the electric potential of the positive terminal is 0 V and that of the negative terminal is −12V. Recall that e=1.60×10−19C.
1.92x10^-18 J
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At the negative terminal of the battery the electron has electric potential energy. What happens to this energy as the electron jumps from the negative to the positive terminal?
It is converted to kinetic energy
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If you wanted to move an electron from the positive to the negative terminal of the battery, how much work W would you need to do on the electron?
1.92x10^-18 J
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The electric potential inside a parallel-plate capacitor __________
increases linearly from the negative to the positive plate
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The field between two charged parallel plates is kept constant. If the two plates are brought closer together, the potential difference between the two plates
Decreases
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New units of the electric field were introduced in this chapter. What are they?.
V/m
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The electron volt is a unit of __________.
energy
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What are the units of potential difference?
volts
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The electric field __________
is always perpendicular to an equipotential surface
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You can increase the capacitance of a capacitor by
Both A and D
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What property of objects is best measured by their capacitance?
the ability to store charge
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Consider an air-filled charged capacitor. How can its capacitance be increased?
Decrease the spacing between the plates of the capacitor.
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Consider a charged parallel-plate capacitor. How can its capacitance be halved?
Double the plate separation Halve the plate area
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Consider a charged parallel-plate capacitor. Which combination of changes would quadruple its capacitance?
Halve the plate separation and double the plate area.
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If the spacing between the plates, d, is the same in both capacitors, and the voltage across capacitor 1 is V, what is the voltage across capacitor 2?
V/2
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If the spacing between the plates in capacitor 1 is d, what should the spacing between the plates in capacitor 2 be to make the capacitance of the two capacitors equal?
2d
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Current from a charged capacitor lights a bulb. As time goes on, the brightness of the bulb
decreases
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You can decrease the resistance of a length of wire by
cooling it
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A lightbulb is rated by the power that it dissipates when connected to a given voltage. For a lightbulb connected to 120 V household electricity, decreasing the resistance of the filament will _____ the current through the bulb and _____ the power dissipated by the bulb
increase, increase
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The charge carriers in metals are _____
electrons
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A battery is connected to a resistor. Increasing the resistance of the resistor will __________
decrease the current in the circuit
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A battery is connected to a resistor. As charge flows, the chemical energy of the battery is dissipated as _________
thermal energy
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The equation I = Δ V/R is called
Ohm's law
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The laws shown in the video—Kirchhoff's junction law and Kirchhoff's loop law—are not newly introduced laws of physics. The junction law is based on __________, and the loop law is based on __________
Conservation of charge, conservation of energy
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In a series circuit of two resistors, the resistors have the same __________; in a parallel circuit of two resistors, the resistors have the same __________
Current through them, voltage across them
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The symbol shown represents a _____
battery
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The bulbs in the circuit below are connected __________
in series
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Which terminal of the battery has a higher potential?
the top terminal
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When three resistors are combined in series, the total resistance of the combination is __________
greater than any of the individual resistance values
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Signal propagation in the nervous system can be modeled as
A series of RC circuits
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In an RC circuit, what is the name of the quantity represented by the symbol τ?
the time constant
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What is the reading V of the voltmeter? Express your answer in terms of the EMF E.
V = E
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The voltmeter, as can be seen in the figure, is connected to points 1 and 3. What are the respective voltage differences between points 1 and 2 and between points 2 and 3?
0;E
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What is the reading I of the ammeter? Express your answer in terms of E and R
I = ER
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What is the reading of the ammeter now? Express your answer in terms of E, r, and R.
I = E/R+r
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What is the reading of the voltmeter now? Express your answer in terms of E, r, and R.
V = ER/R+r
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Rank below the three identical resistors (A, B, and C) in (Figure 1) on the basis of the current that flows through them. Rank from largest to smallest. To rank items as equivalent, overlap them.
A = B,C
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Rank below the three identical resistors (A, B, and C) in (Figure 2) on the basis of the current that flows through them. Rank from largest to smallest. To rank items as equivalent, overlap them.
C, A=B
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Rank below the four identical resistors (A, B, C, and D) in (Figure 3) on the basis of the current that flows through them. Rank from largest to smallest. To rank items as equivalent, overlap them.
D, A, B=C
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How does the current through R1 compare with the current through R2 immediately after the switch is first closed?
The current through R1 is greater than the current through R2.
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How does the current through R1 compare with the current through R2 a very long time after the switch has been closed?
The current through R1 is equal to the current through R2.
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How does the current through R1 compare with the current through R2 immediately after the switch is opened (after being closed a very long time)?
The current through R1 is less than the current through R2.
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Magnetic field lines form closed loops
All of the above.
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Compasses line up with magnetic fields. A compass will line up
Parallel to magnetic field lines, with the north pole pointing in the direction of the field
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A compass in a magnetic field will line up __________
with the north pole pointing in the direction of the magnetic field
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The direction of the magnetic force on a moving charged particle in a magnetic field is __________
both perpendicular to the velocity and perpendicular to the magnetic field
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A magnet will exert a force on
All of the above
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The magnetic field lines due to a straight, current-carrying wire are __________
circles around the wire
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A loop of wire carries a current. The resulting magnetic field __________
is similar to that of a bar magnet perpendicular to the plane of the loop
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Two parallel wires carry a current in the same direction. There is ___________ between the wires
an attractive force
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The magnetism of a permanent magnet results from __________
the magnetic moments of electrons in the material making up the magnet
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In this video, we see that a _____ magnetic field can create an electric current
changing
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Which of the following will cause an induced current in a coil of wire?
a magnet being moved into or out of the coil
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Lenz's law states that an induced magnetic field in a conductor
Opposes the change in flux through the conductor
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A metallic conductor moving at a constant speed in a magnetic field may develop a voltage across it. This is an example of __________
motional emf
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An emf is induced in response to a change in magnetic field inside a loop of wire. Which of the following changes would increase the magnitude of the induced emf?
changing the magnetic field more rapidly
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In a transformer, energy is carried from the primary coil to the secondary coil by