AP Physics 2 Midterm
The electrical resistance of the part of the circuit shown between point X and point Y is
1 1/3Ω
In the diagram above, what is the equivalent capacitance between points P and Q ?
24μF
Real gases do not always exhibit the behavior assumed for ideal gases. Suppose one nitrogen atom in a sample of gas is moving with speed vv when it collides with and sticks to an oxygen atom that is momentarily stationary. How do the linear momentum and kinetic energy of the two-atom system after the collision compare to these quantities before the collision?
Linear Momentum and Kinetic Energy are both less
Two negatively charged balloons are suspended from the ceiling by insulating strings, as shown in figure 1. Free-body diagrams showing the tension force FTFT , electric force FEFE , and gravitational force FgFg on each balloon are shown in figure 2. If the amount of negative charge on each balloon increases, how should the length of the vectors shown in the figure be changed?
The electric and tension force vectors should be longer, and the gravitational force vector should remain the same.
If the diameter of the exit holes increases by a factor of 22 , the velocity of the exiting water will
decrease by a factor of 4
Two charged particles, XX and YY, are fixed on a grid as shown in the figure. The particles have the same amount of charge but with opposite signs, as shown. Which of the following best represents the direction of the net electric field at point pp due to the two particles?
down arrow
Two point charges with charges Q1=+2μCQ1=+2μC and Q2=−4μCQ2=−4μC are located on the horizontal axis, as shown in the figure. The distance between their centers is 1.0m1.0m. Point P is midway between the point charges. Which of the following is the best visual representation of the electric field vectors from both Q1Q1 and Q2Q2 at point P?
Both Arrows pointing to the right
A positively charged rod is brought near a neutral conducting sphere that is grounded. While the rod is near the sphere, the ground is disconnected. The rod is then removed. Which of the following best describes the net motion of charged particles that results in the final charge on the sphere?
Electrons move onto the sphere.
A sample of an ideal gas with initial volume VV is compressed isothermally until its volume is V2V2. Which of the following claims is correct about the transfer of energy by heating and the work done on the gas?
Energy Transferred by Heating: Out of the gas Work Done on the Gas: Positive
A hollow sphere with mass 100.0kgnand volume 0.50m3 is submerged in water with density 1000kgm3 and is being held at rest by a rope of negligible mass, as shown in the figure. The buoyant force on the sphere is the product of its volume, the water density, and the acceleration due to gravity. Which of the following shows a correct free-body diagram for the sphere?
F Buoyant Up 5000N FT down 4000N FG down 1000N
One end of a hose is connected to an elevated water tank and the other end is capped, as shown in the figure. The normal force exerted on the hose by the ground has magnitude FN. Then, a small hole is cut into the hose, causing water to spray upward. Which of the following correctly describes the magnitude of the normal force exerted by the ground on the hose after the hose has been cut?
It is greater than FN because the water exiting the hole exerts a downward force on the hose.
A neutral metal ball is suspended from a light insulating string and hangs vertically downward. A negatively charged rod is brought near the metal ball, and the metal ball is observed to move toward the negatively charged rod. Which of the following best describes the observed behavior of the neutral metal ball?
The negatively charged rod induces charge separation within the metal ball, so the side of the ball closest to the rod is positively charged.
An ideal gas is sealed in an insulated container with a movable piston. What happens to the temperature of the gas as it is compressed?
The temperature increases.
Three identical metal spheres, AA, BB, and CC, are on insulating stands, as shown in the figure. Initially, sphere AA has a net charge of qq and spheres BB and CC are uncharged. Sphere BB is first touched to sphere AA and then separated from it. Next sphere AA is touched to sphere CC and then separated from it. What is the resulting charge on sphere CC?
q/4
Students are performing an experiment to determine how changing the area of the plates of a parallel-plate capacitor affects its behavior in a circuit. They connect a capacitor with plate area A to a battery and allow it to become fully charged. They take measurements that they believe will allow them to calculate the charge q on one plate of the capacitor. The students then repeat the procedure with other capacitors. The capacitors each have a different plate area but are otherwise identical. The students plot the calculated charge q as a function of plate area A. Their results, including a best fit to the data, are represented above. Is this graph a reasonably accurate representation of the relationship between q and A?
No, because the relationship should result in a graph that is linear and increasing
One mole of an ideal gas is sealed in a cylindrical container with a movable piston. The volume and pressure of the gas are recorded as the gas is taken through process ABCAABCA, as shown in the graph. Which of the following features of the graph, if any, is equivalent to the amount of work done on the gas during the complete cycle?
The area bound by the triangle ABCA
A sphere is dropped into a large body of water. The sphere then moves downward through the water. Three forces are exerted on the sphere during its descent: the water exerts a frictional force Ff on the sphere, the water exerts a buoyant force Fb on the sphere, and Earth exerts a gravitational force Fg on the sphere. The free-body diagram depicts the direction and relative magnitude of these forces at an instant during the sphere's motion. Which of the following describes the acceleration of the sphere at this instant?
g(Fg−Fb−Ff)/Fg
A spherical shell has a net positive charge that is evenly distributed. A small positively charged particle moves freely in the vicinity of the sphere. No external forces are exerted on the system. In figure 1, the particle moves from the center of the shell to a distance dd from the center. In figure 2, the particle is outside the shell and moves a distance dd farther away from the center. Which of the following correctly describes the change in the internal energy of the particle-shell system for each case?
Remains the Same for Both
A liquid at rest in a fixed container exerts a force perpendicular to the wall of the container. Two students make claims about the microscopic cause of this force. Student A says that the force exerted by individual molecules as they bounce off the wall is always perpendicular to the wall. Student B says that the molecules may strike the wall at angles that are not perpendicular. Which student is correct and why?
Student BB. The molecules in a liquid are in random motion at the microscopic scale. For every atom that hits at an angle to one side of perpendicular, there is likely to be another atom hitting at the same speed at the same angle on the other side of perpendicular. On average the nonperpendicular components cancel.
A student is performing an experiment that involves the charge on a metal cup that is attached to an uncharged electroscope. A charged rod is lowered into the cup without touching the sides of the cup. As a result the leaves of the electroscope separate. The rod is then removed from the cup, and the leaves return to their unseparated position. The student repeats the procedure, but this time the electroscope is grounded and the ground is removed before the rod is removed from the cup. The leaves then remain separated. What can be concluded about the charge on the separated leaves of the electroscope?
The leaves have a charge in each trial, but the sign of the charge cannot be determined.
A student plans to determine the resistivity of a specific type of metal. To do this, the student will use wires constructed of the metal with known dimensions that are connected to a variable power source. The potential difference across and the current through each wire are measured and the resistance of each is calculated. The resistance is used to determine the resistivity. Which of the following should be kept constant to ensure that the resistivity values are consistent, and why?
The temperature of the wires, because resistivity changes with temperature.
A small metal sphere X is charged by losing 500 electrons. An identical metal sphere Y is charged by gaining 1000 electrons. The two spheres are first put in contact with each other and then separated. If -e is the charge on an electron, what is the charge on each sphere after separation?
-250e -250e
The graph shows the electric potential along the x−x−axis in a region of space. What is the magnitude of the average electric field between x=2mx=2m and x=4mx=4m?
30V/m
A capacitor with capacitance C0 has a charge Q0. It is then connected in a circuit with a switch and an initially uncharged capacitor with capacitance C0 / 3 , as shown in the figure above. What are the final charges on the capacitors a long time after the switch is closed?
3Q0/ 4 and Q0/4
The dashed line in the figure shows a stream of water from the end of a horizontal hose with an opening of diameter 2cm2cm . The water lands a horizontal distance dd from the end of the hose. With the water pressure remaining the same, the diameter of the opening is decreased from 2cm2cm to 1cm1cm . At what horizontal distance from the end of the hose will the stream of water now land?
4d
A boat is moving to the right on the surface of a lake. At one instant, the following forces are exerted on the boat: 120N of thrust from the water on the boat's propeller, 50N of drag from the water, 5N of drag from the air, 550N of buoyant force from the water, and 550N of gravitational force. Which of the following correctly indicates the direction and magnitude of the net force exerted on the boat?
65N to right
The circuit shown above contains a capacitor, a battery, and four lightbulbs, AA, BB, CC, and DD, with the same resistance. The circuit has been connected for a long time. The capacitor is now removed from the circuit and replaced with a connecting wire. Which bulbs are dimmer at equilibrium in the second circuit compared to the first circuit?
B
The figure shows an insulated bottle containing some hot coffee. The outer wall has a small hole in it so that air will fill the space between it and the inner wall. Which of the following describes the primary processes by which energy moves from the hot coffee to the outer wall of the container?
Conduction and convection
Two ideal gas molecules with identical masses travel toward each other as shown in the figure. Molecule AA has an initial velocity of 2v02v0 to the right and molecule BB has an initial velocity of v0v0 to the left. The molecules collide head-on. Which of the following claims correctly describes their motion after the collision?
Determining the magnitudes of their velocities includes applying conservation of kinetic energy because the collision is assumed to be elastic.
The figure shows an electron ee that is at the center of a square configuration of fixed particles. Each particle has a charge of magnitude qq and sign as shown. Which of the following is a correct force diagram for the electron?
Double Arrows Pointing up
The blimp shown in the figure has volume 120m3 and is filled with a gas of density 0.19kg/m3. The materials that the blimp is made of (not including the gas) have a total mass of 50kg. The air surrounding the blimp has density 1.2kg/m3. The blimp is held at rest by a rope with tension TT. Which of the following free-body diagrams correctly indicates the forces acting on the blimp and the magnitude of T?
FBuoyant up WGas and WBimp Down T Down 712
A wire of known dimensions is connected to a power source set to a low potential difference. The current through the wire is measured, and its resistance is calculated. The power source is set to a very high potential difference, and the measurement and calculation are repeated. Must the two calculated resistance values always be the same, and why or why not?
No, because if the wire heats up enough, its resistivity may change significantly.
A student has four pieces of a substance in different shapes and sizes. The student wants to determine the density of the substance. Which of the following procedures would yield the most accurate data?
Place the pieces on a mass balance, one at a time and record the mass of each. Submerge the pieces one at a time in a graduated cylinder filled with a volume of water and record the volume change.
A student has parallel plate capacitors with the same plate separation and dielectric material, but different known plate areas. The student wants to experimentally determine the effect of plate area on capacitance. The student connects each capacitor in the circuit shown above. Which of the following indicates quantities to be measured that will provide useful information and explains why the information is useful?
Potential difference across the capacitor and charge on it a short time after the switch is closed, because that will allow the capacitance to be determined.
Which of the following is a representation of data that support the statement "An electric charge smaller than the elementary charge has not been isolated"?
Skinny curves upward facing, starting at origin
The figure shows a region of uniform electric field with magnitude 0.2N/C0.2N/C, represented by the vertical electric field vectors. The dashed horizontal lines represent lines of uniform electric potential. The electron is released from rest in the electric field. What is the speed of the electron after it has moved 0.04m0.04m, and has the electron moved to a position of higher or lower electric potential? Gravitational effects are negligible.
Speed: 5.3×10^4m/s, Electric Potential: Higher
In the kinetic theory of gases, it is assumed that collisions between particles in an ideal gas are perfectly elastic. Which of the following claims is true based on this assumption?
The average kinetic energy of the gas particles does not change due to interactions between particles.
A resistor and an initially uncharged capacitor are connected in series with a battery. A long time after the circuit is connected, which of the following is true?
The current in the circuit is zero.
A student is modeling the flow of air around an airplane wing, as shown in the figure. The model assumes that the air behaves like a fluid. Which of the following can exert an upward force on the wing?
The difference in the normal forces exerted on the wing by the air above and below the wing
One mole of an ideal gas is sealed in a cylinder with a moveable piston. The temperature of the gas inside the cylinder increases from 0°C0°C to 100°C100°C as the gas expands, as shown in the figure. Which of the following correctly justifies the change, if any, of the internal energy of the gas?
The internal energy of the gas increases because the average kinetic energy of the gas molecules increases.
After the switch is closed and the circuit has reached a steady state, an ideal ammeter is connected between points X and Y, as shown above. The circuit is again allowed to reach steady state. Which of the following correctly indicates the reading on the ammeter and explains why it has that reading?
The same as the current in resistor 1, because ammeters have very low resistance and it will create a short between the top and bottom wires.
A large water tank with area AtAt has an open spigot of area AsAs, as shown in the figure. Water exits the spigot with speed vsvs, and the speed of the water at the top of the tank is vtvt. The pressure of the water exiting the spigot is PsPs, and the pressure of the water at the top of the tank is PtPt. If At≫AsAt≫As, which of the following is true?
vt≪vs
A wire of length L and radius r has a resistance R. What is the resistance of a second wire made from the same material that has a length L/2 and a radius r/2 ?
2R
Students rub air-filled balloons on their hair and then touch the charged balloons to the ceiling. The balloons initially stick to the ceiling but after some time eventually fall back down. Which of the following claims best describes the physical processes responsible for these observations?
The balloons induced charge separation in the ceiling, resulting in an attractive force. Over time, conduction of electrons into the air reduced the net charge of the balloons.
A student wants to compare the thermal conductivities of several metal rods with different lengths LL and cross-sectional areas AA. The student connects each rod to two reservoirs, one containing a hot liquid at temperature 100°C100°C and the other containing an ice bath at 0°C0°C, as shown in the figure. Each rod is kept in contact with the reservoirs for the same fixed time interval ΔtΔt. Let QQ be the amount of energy transferred through a rod in the time ΔtΔt. Which of the following lists all the additional quantities that must be measured to be able to compare the thermal conductivities?
Q, L, and A
A small toy is submerged in a plastic bottle filled with water. The toy is initially at rest in the middle of the bottle. There is a small hole in the bottom of the toy, and the toy is partially filled with water. When the bottle is squeezed, more water is forced into the toy, compressing the air inside and increasing the overall density of the toy. The buoyant force exerted on the toy by the water is equal to the product of the volume of the toy, the density of the water, and the acceleration due to gravity. Which of the following free-body diagrams could represent the relative magnitudes of the forces exerted on the toy after the bottle is squeezed?
F Buoyant up 1 FG down 2
A block is submerged in a container of fluid. Which of the following describes the microscopic cause of the force that the fluid exerts on the block?
The electrostatic force between the electrons in the molecules of the block and the electrons in the molecules of the fluid
Three identical conducting spheres are arranged on insulating stands and equally spaced, as shown. Sphere 1 initially has a net charge of Q0Q0 , while spheres 2 and 3 are initially uncharged. Sphere 1 is touched briefly to sphere 2 and moved away; then sphere 2 is touched briefly to sphere 3 and moved away. An external force moves sphere 3 a distance dd to the right, and sphere 3 returns to rest. During this process, the external force does an amount of work +W+W on sphere 3. How much total work do the electric forces from spheres 1 and 2 do on the system containing only sphere 3 during this process?
−W
A student predicts that the density of salt water is higher than the density of drinking water. The student has a beaker filled with salt water, a beaker filled with drinking water, and a cube that is hung from a spring scale. The cube will sink in both liquids. What measurements are needed to verify the student's prediction?
The spring scale reading with the cube submerged in each liquid only
The figure shows two point charges with equal positive charge and three labeled points, all of which lie on the same line. Which of the following best shows the electric field in the plane of the page and near the two charges, which are represented by the two dots?
Arrows pointing out of both
A student in an electronics lab is studying the electrical properties of pieces of graphite. The student applies a potential difference of 24 V across the length of a cylindrical piece of graphite with a radius of 0.5 mm. The student has another piece of graphite of the same length but with a radius of 0.7 mm. The student wants the same current in both pieces of graphite. What potential difference should the student apply across the 0.7 mm piece?
12 V
A sealed cylinder with a movable piston contains NN molecules of an ideal gas. The gas is initially in the state with pressure P0P0 and volume 3V03V0 shown on the graph of pressure PP as a function of volume VV. The gas is then taken through the two processes shown. How much energy is exchanged between the system and its surroundings by heating as the gas is taken through the two processes, and is the energy added to or removed from the gas?
2P0V0 removed
A triangular block is underwater and slowly rising to the surface. Which of the following best represents the forces exerted by the water on the surfaces of the block?
3 Arrows up 1 Down 4 Facing inward with smaller arrows toward the to and longer by bottom
A jar contains vinegar and oil that have separated into layers, as shown in the figure. Which of the following correctly identifies a Newton's third law force pair?
The weight of the vinegar and the gravitational force of the vinegar on Earth
In a mixture of gases, a carbon atom of mass 12m12m is moving to the right with speed vv when it collides with and sticks to an oxygen atom of mass 16m16m moving to the right with speed v/2v/2 . What is the final speed of the resulting molecule?
5/7v to the right
A gas-filled balloon has a total average density of 0.2ρ0.2ρ. The air surrounding the balloon has a density of ρρ. The balloon is released from rest in a constant horizontal breeze directed north. If air resistance is negligible, what is the shape of the path followed by the balloon?
A straight path toward the north and angled upward
Water exits a water fountain atn45° to the horizontal, as shown. To get the water to reach the ground farther from the fountain, an adapter is added to the fountain that decreases the size of the hole that the water exits. Which of the following explains why this approach will work?
Because the mass flow rate must be constant, the smaller opening will result in the water exiting the fountain with a greater speed. A greater vertical speed means the water will spend more time in the air, and a greater horizontal speed adds to the increase in distance that the water can travel.
The figure shows two point charges, one positive and one negative, separated by a distance rr . The magnitude of the charge on each point charge is qq . If the initial force between the point charges is F0F0 , what will the magnitude of the force between them be if the separation distance is increased to 3r3r and the magnitude of each charge is increased to 3q3q ? Ignore gravitational effects.
F0
Negatively charged object AA is attached to an uncharged wall made of insulating material. Negatively charged object BB is connected to the wall by an insulating string. When object BB comes to rest, it is displaced an angle θθ from the wall, as shown. A free-body diagram for object BB is also shown, with the magnitudes of the forces labeled. Which of the following is correct for the forces on object BB?
FE=Tsinθ,mg=Tcosθ
Which of the following correctly compares the magnitude FgFg of the gravitational force and the magnitude FEFE of the electrostatic force exerted between two electrons?
FE>FgFE>Fg, because the product of the charge of an electron and the Coulomb's law constant kk is greater in magnitude than the product of the mass of an electron and the universal gravitational constant GG.
The pressure that a liquid exerts on the bottom surface of a container is the net result of individual molecules in the liquid that collide with the surface. Which of the following correctly indicates and justifies the relationship between the force exerted on the surface by a molecule and the force exerted on a molecule by the surface during a single one of these collisions?
Fmoleculeonsurface=Fsurfaceonmolecule, because the force the molecule exerts on the surface is equal and opposite to the force the surface exerts on the molecule.
A block of mass M is at rest at the bottom of a container full of liquid. Let WW be the magnitude of the weight of the block, let FB be the magnitude of the buoyant force on the block, and let N be the magnitude of the normal force exerted on the block by the bottom of the container. Which of the following is a correct expression of Newton's second law for the block?
Ma=W−N−FB
The figure shows a system of three spheres that are isolated from other objects. The small sphere with charge −q−q is released from rest on the x−axisx−axis, far from the other two spheres. The two spheres with charge +Q+Q are held fixed at the same distance from the axis. Gravitational effects are negligible. Which of the following pairs of graphs best represents the potential energy UU of the system and the kinetic energy KK of the moving sphere as a function of the position xx of the moving sphere?
Going up into U, Going down out of K
The following data are obtained from various sources and investigations. Based on these data, which of the following represents the order of the substance densities ranked from greatest density to least density?
Gold, silver, copper, iron
Water flows with speed vv through a horizontal, cylindrical pipe. Which of the following changes in the geometry of the pipe will double the speed of the water in the pipe?
Halving the area of the pipe
Students want to figure out which force, the gravitational force or the electric force, has more impact at different scales in the universe. They choose two scenarios: a hydrogen atom consisting of a proton and an electron, and a solar system consisting of a star and a single planet. Which of the following best describes which force has more impact at each of these two scales?
Hydrogen is electric, solar system is gravitational
Three conducting spheres on insulating stands are arranged as shown in the figure. Spheres AA and BB are identical but have different charges as shown. Sphere CC is smaller than the other two spheres and is uncharged. Sphere AA is touched to sphere BB, and the spheres are then separated. Next, spheres BB and CC are touched and separated. What is the final charge on Sphere CC?
Less than 1.5Q
A student has three objects of different shapes, as shown, and wants to compare their densities using liquids of known density. Which of the following experimental methods will allow the comparison to be made?
Let each object float in the same liquid, and compare the fractions of the objects' volumes that are below the liquid surface.
Which of the following best explains the entropy of an isolated system as it is taken through an irreversible thermodynamic process?
The entropy increases because the system becomes more disorderly.
A volume ΔVΔV of an ideal fluid enters the left side of a cylindrical pipe with speed v1v1 during a time interval ΔtΔt, and an equal volume ΔVΔV of ideal fluid exits the right side of the pipe with speed v2v2 during the same time interval ΔtΔt. The cross-sectional areas of the left end and right end of the pipe are A1A1 and A2A2 , respectively; the pressures at the left end and right end of the pipe are P1P1 and P2P2 , respectively; and the distance between the centers of the two sections is ΔhΔh , as shown in the figure. Which equation and description best expresses the motion of the ideal fluid in the cylindrical pipe in terms of conservation of energy?
P1+12ρv21=P2+ρgΔh+12ρv22. The speed of a fluid at two different locations in a pipe depends on the pressure of the fluid at each location and the work done by gravity on the fluid as it moves from one location to the other.
Identical blocks 1 and 2 are placed into contact with each other. The temperature of block 1 is initially greater than the temperature of block 2. What quantity is transferred between the blocks and what is the direction of the transfer?
Quantity Transferred: Molecular kinetic energy Direction of Transfer: From block 1 to block 2
Students are investigating charge separation in conductors. They have two initially neutral conducting spheres and two different kinds of cloths. The students want to determine if the cloths add the same kind of charge or opposite kinds of charge when rubbed on the spheres. Which of the following procedures will provide enough information to determine whether the cloths add the same or opposite charges?
Rub one sphere with one cloth and the other sphere with the other cloth, and bring them close together without touching. See if they attract or repel.
Spheres AA and BB are identical in size and made from the same conducting material. Sphere AA is attached to an insulating rod, and sphere BB is suspended from an insulating thread. Sphere AA initially has a charge of +10 nC+10 nC, and sphere BB is initially uncharged. Which of the following best represents the distribution of charge on the surfaces of spheres AA and BB when sphere AA is brought near sphere BB?
Sphere A: positive charges on the right side; Sphere B:4 positive on the right and 4 negative on the left
Ice cubes are added to an insulated cup of hot water. As a result, the temperature of the water decreases and the ice melts. What statement best explains the change in entropy of the system, which is the combination of water and ice cubes, on a molecular level?
The entropy of the system increases, because the disorder caused by the change in state from solid to liquid water causes more disorder than liquid water cooling causes order.
The figures show situation 1 and 2. In situation 1, a positively charged 0.10kg0.10kg insulating sphere is suspended at rest 0.10m0.10m above a large positively charged metal plate. In situation 2, a positively charged 0.20kg0.20kg insulating sphere is located 0.20m0.20m above the positively charged metal plate and is in motion. The magnitudes of the charges on the spheres are the same. Which of the following best explains why sphere 1 can remain motionless?
The electric force between sphere 1 and the positively charged plate is equal to the force of gravity between sphere 1 and Earth.
An electron and a proton are held near each other. Which of the following correctly compares the magnitude of the gravitational and electric forces that the particles exert on each other for different separation distances?
The gravitational force is always less than the electric force.
Which of the following gives correct reasoning about the water's properties as it moves from point AA to point BB ?
The increase in gravitational potential energy of the water-Earth system and in the kinetic energy of the water causes a decrease in water pressure.
Not all gases are ideal, including water vapor. Two water vapor molecules, AA and BB, are initially moving with different speeds in opposite directions when they collide head-on, causing molecule AA to stop. If there are no external forces on the system of two molecules, which of the following statements must be true?
The system loses kinetic energy as a result of the collision.
A student does an experiment to measure the charge on various drops of oil and collects the data shown. How do the data relate to the claim that the elementary charge has a value of 1.6×10−19C1.6×10−19C?
They support the claim, because all the values are integer multiples of that number.
Three identical conducting spheres are arranged on insulating stands and equally spaced, as shown. Sphere 1 initially has a net charge of Q0Q0 , while spheres 2 and 3 are initially uncharged. Sphere 1 is touched briefly to sphere 2 and moved away; then sphere 2 is touched briefly to sphere 3 and moved away. After the processes, in which direction, if any, is the net electric force exerted on sphere 2 ?
To the right
At the instant shown in Figure 1, a particle with charge −q−q is moving with speed vv in the +x+x -direction. An electric force is exerted on the particle in the +y+y -direction, as shown in the free-body diagram in Figure 2. In which direction is the acceleration of the particle?
Up Arrow
An engineer has four wires made of the same material and wants to determine the material's resistivity. The engineer measures the length L and cross-sectional area A of each wire. The engineer then applies a potential difference V across each wire and measures the resulting current I. To estimate the resistivity of the material using only the slope of a graph of the data, which of the following should be graphed as a function of L/A?
V / I
Isolines of the electric potential due to two point charges, represented by dots, are shown. The point charges have equal magnitudes and unknown signs. If the electric potential is zero at an infinite distance from the charges, which of the following is true about the electric potential VV and the magnitude EE of the electric field midway between the charges?
V≠0 and E=0
The following quantities are measured for a cylindrical wire connected in a circuit: potential difference across the wire, current in the wire, length of the wire, and cross-sectional area of the wire. Which of the following correctly indicates whether or not each quantity is needed to determine the resistivity of the wire?
Yes, Yes, Yes, Yes
The table above shows experimental data for the capacitance CC of a parallel-plate capacitor as a function of the plate separation SS. The students who took the data neglected to record their units. Do the data support the accepted relationship between capacitance and plate separation? Why or why not?
Yes, because the data show that CC is proportional to 1/S.
A student heats a sample of gas in a cylinder with a movable piston and a pressure gauge. The student measures the volume and pressure of the gas as the gas is heated. The student's data is plotted in the graph above. Which of the following gives the best estimate of the work done by the gas on its surroundings during the motion of the piston?
0.7×10^5 J
The dashed line in the figure is equidistant from two positively charged plates. A small positively charged object is placed at point PP and released from rest. Assuming gravitational effects are negligible, which of the following correctly predicts how the kinetic energy of the object will change, if at all, after it is released?
The kinetic energy of the object will begin to increase and continue increasing because the electric field along the dashed line is nonzero and directed to the right for all finite distances from the plates.
The students are required to create a procedure to determine the thermal conductivity of the rod. They first determine that they can measure the amount of ice that has melted after a given time to calculate the heat transfer over time to the block of ice. Which of the following must the students also measure to calculate the thermal conductivity of the rod?
The temperature of the ice
The figure above shows a battery and an open switch connected to two resistors and a capacitor. The switch is closed, and the circuit reaches a steady state. Then the switch is opened again. Which of the following best describes the current in resistor XX immediately before and immediately after the switch is opened again?
Zero before and nonzero after
A gas-filled balloon is moved from a warm room to a cold refrigerator. The gas contracts, so the balloon does work WW on the gas and the gas loses thermal energy QQ to its surroundings. Which of the following indicates and justifies the correct form of the first law of thermodynamics during this process?
ΔU=−Q+W, because thermal energy is transferred to the surroundings and work is done on the gas.
An object is held in equilibrium, submerged in a fluid by a piston. Which of the following is a possible free-body diagram for the object?
FFluid up 2 FGravity Down 1 FPiston down 2
The rod is removed from the apparatus and placed in a warm room until it reaches thermal equilibrium. Its ends are then positioned to touch the ends of an identical rod with a much colder temperature, as shown in the figure. Which of the following is the best explanation of how energy is transferred between the rods as they approach thermal equilibrium?
Quickly vibrating molecules in the warm rod collide with slowly vibrating molecules in the cold rod, and on average the slower molecules begin to vibrate faster.
A downward-directed faucet has a diameter of 2.0cm2.0cm, as shown in the figure. A stream of water leaves the faucet with the same diameter and a speed of 2.0m/s2.0m/s. Which of the following describes a correct method to determine the diameter of the stream at a distance of 3.0m3.0m below the faucet?
The water falls freely, so the equation v2=v20−2aΔx can be used to find the new speed of the water. Then the equation of continuity A1v1=A2v2 can be applied to find the new diameter of the stream.
