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Which of the following best describes the movement of an electron after it is ejected from the cathode? A. It is stationary until collisions propel it toward the anode. B. It moves with constant speed toward the anode. C. It accelerates toward the anode. D. It exits through a side of the vacuum photodiode.
AAMC Standard Solution: A charged particle accelerates in an electric field. The electron starts with a velocity that increases as it approaches the anode through the vacuum.
Which of the following describes the direction of the magnetic force on an ion moving in an artery past a flowmeter? A. Parallel to both the direction of v and the direction of B B. Parallel to the direction of v and perpendicular to the direction of B C. Perpendicular to the direction of v and parallel to the direction of B D. Perpendicular to both the direction of v and the direction of B
AAMC Standard Solution: A magnetic force acts on a moving charge in a direction that is perpendicular to both the velocity of the charge and the direction of the magnetic field. This is a basic law of the interaction of electric currents and magnetic fields. Thus, answer choice D is the best answer.
Which of the following will occur when the magnet used in the flowmeter discussed in the passage is replaced with a stronger magnet? A. The electric field will reverse polarity. B. The electric field will decrease. C. The voltage will increase. D. Blood will flow faster.
AAMC Standard Solution: A stronger B field increases the magnetic force, Fm = q v B^. The electric force must also increase to achieve equilibrium. This implies a larger electric field in the artery and a larger voltage across the artery. Thus, answer choice C is the best answer.
Which of the following graphs best illustrates how the force between fragments from the fission of a uranium nucleus varies as the fragments move away from each other? A. B. C. D.
AAMC Standard Solution: According to Coulomb's law, the repulsive force versus fragment separation (r) has a 1/r2 dependence. Graph D shows this behavior.
The process taking place at the cathode was: A. oxidation by a loss of electrons. B. oxidation by a gain of electrons. C. reduction by a loss of electrons. D. reduction by a gain of electrons.
AAMC Standard Solution: According to the passage, H2(g) was produced at the cathode. The reaction taking place at the cathode was 2H+(aq) + 2e- → H2(g), which means the H+ was gaining electrons and undergoing reduction. Thus, D is the best answer.
What is the magnitude of the electric field between the two electrodes in ionization type detectors? A. 1.5 N/C B. 1.66 N/C C. 15 N/C D. 166 N/C
AAMC Standard Solution: An electric field can be given in volts per meter. This means the electric field value is 5/(0.03) = 166.7 V/m. Because 1 V ≡ 1 J/C, the electric field value 166.7 V/m = 166.7 N/C. Thus, D is the best answer.
Which of the following changes to the circuit will decrease the electric field between the electrodes by the greatest amount? A. Increasing L by a factor of 2 B. Decreasing L by a factor of 2 C. Increasing R by a factor of 2 D. Decreasing R by a factor of 2
AAMC Standard Solution: For a fixed voltage between cathode and anode, the electric field is inversely proportional to the distance between them. Increasing the circuit resistance for a fixed current will decrease the electric field, but not by as much as does the length change. E = (V − IR)/L
At which electrode is aluminum produced in a galvanic cell and in an electrolytic cell? A. At the anode in both cells B. At the cathode in both cells C. At the anode in the galvanic cell and cathode in the electrolytic cell D. At the cathode in the galvanic cell and anode in the electrolytic cell
AAMC Standard Solution: Reduction of the Al3+ to form Al(s) occurs at the cathode both in a galvanic and in an electrolytic cell. Thus, B is the best answer.
Which circuit elements store energy? Capacitors Resistors Batteries A. I only B. I and II only C. I and III only D. II and III only
AAMC Standard Solution: The capacitor charges up and stores energy in the electric field between the places. The energy stored is ½CVc2, where Vc is the voltage across the capacitor. The battery is the source of energy for the circuit and thus is a store of energy. The resistor is not a storage device for energy and answer C is the correct answer.
Which of the following describes the direction of motion of alpha, beta, and gamma rays in the presence of an external magnetic field? A. They all travel straight. B. They are all bent in the same direction. C. Gamma rays travel straight; alpha and beta rays are bent in the same direction. D. Gamma rays travel straight; alpha and beta rays are bent in opposite directions
AAMC Standard Solution: The examinee must decide how alpha particles, beta particles, and gamma rays will be influenced when they move in a magnetic field. Magnetic fields exert a force on moving electric charge. The magnitude of the force is directly proportional to the electric charge and particles of opposite sign experience forces of opposite direction. Gamma rays possess zero charge, and thus experience no force from a magnetic field and will travel in a straight line. Alpha and beta particles possess charges of opposite sign, and thus will experience forces in opposite directions- so their trajectories will bend oppositely. Thus, D is the best answer.
Which of the following statements is consistent with the incorrect conclusion that HCl is an ionic compound? A. It is a gas at room temperature. B. A 1 M solution freezes below 0°C. C. A 1 M solution conducts electricity. D. It is composed of two nonmetals.
AAMC Standard Solution: The passage states that an aqueous solution of an ionic compound conducts electricity. Thus, C is the best answer.
At a given temperature, the resistance of a wire to direct current depends only on the: A. voltage applied across the wire. B. resistivity, length, and cross-sectional area. C. inductance, length, and cross-sectional area. D. resistivity, length, and capacitance.
AAMC Standard Solution: The resistivity relation at a fixed temperature is Thus, B is the best answer.
When switch S is closed to the left, charge begins to accumulate on the capacitor. Charge cannot accumulate indefinitely because: A. the variable resistor inhibits the current flow. B. the battery continually loses charge. C. successive charges brought to the plates are repelled by charges accumulated earlier. D. the fixed resistor loses energy to heat.
AAMC Standard Solution: The two plates of the capacitor collect charges of opposite sign. As more charge arrives it is harder and harder to fill the plates until finally an equilibrium occurs, thus C is correct.
The resistance of the variable resistor, R, at the beginning of the discharge process is: A. 2000 Ω. B. 3000 Ω. C. 4000 Ω. D. 6000 Ω.
AAMC Standard Solution: With 12 Volts initially across the capacitor during its discharge (the capacitor will charge to the battery voltage of 12V) and a current of 0.002 A as found in Figure 2, then the initial resistance R must have been R = V/I = 12/0.002 = 6000 W. This is answer D.
To keep the current constant during the discharge cycle: A. the resistance R must be continually increased. B. the resistance R must be continually decreased. C. the resistance r must be continually increased. D. the resistance r must equal R.
As the capacitor discharges the voltage across it falls, thus to maintain a constant current, R must be proportionately reduced. This is so from Ohm's law, I = V/R. To keep I fixed, R must fall with V. This is answer B.
Which image best illustrates the electric field lines between the inside of an axon and the surrounding extracellular solution? A. B. C. D.
By definition, electric field lines exit from positive and enter negative charges. The axon is negatively charged and the extracellular solution has a zero net potential, thus electric field lines have the direction perpendicular to the one shown in this image.
Making which of the following changes to a circuit element will increase the capacitance of the capacitor described in the passage? A. Replacing the 500-Ω resistor with a 250-Ω resistor B. Replacing the 10-V battery with a 20-V battery C. Increasing the separation of the capacitor plates D. Increasing the area of the capacitor plates
Capacitance C depends on geometric factors only, and in the case of parallel plates, C is proportional to the plate area and inversely proportional to the separation distance of the plates. Thus, D is the best answer.
The electric field inside each of the conductors that forms the capacitor in the defibrillator is zero. Which of the following reasons best explains why this is true? A.All of the electrons in the conductor are bound to atoms, and thus there is no way for an external electric field to penetrate atoms with no net charge. B.Free electrons in the conductor arrange themselves on the surface so that the electric field they produce inside the conductor exactly cancels any external electric field. C.Free electrons in the conductor arrange themselves on the surface and throughout the interior so that the electric field they produce inside the conductor exactly cancels any external electric field. D.All electrons in the conductor, both free and bound, arrange themselves on the surface so that the electric field they produce inside the conductor exactly cancels any external electric field.
Conductors contain both atom-bound electrons and free electrons. Free electrons arrange themselves on the surface of conductors, and their collective electric field produced inside the conductor cancels any external electric field. The resulting electric field inside the conductor is zero.
If the speed of the charged particle described in the passage is increased by a factor of 2, the electrical force on the particle will: A. decrease by a factor of 2. B. remain the same. C. increase by a factor of 2. D. increase by a factor of 4.
Electrical force depends on the particle's charge and the strength of the electric field experienced by the particle, not on the particle's speed. Thus, B is the best answer.
In the schematic diagram shown in Figure 1, the Cd electrode is: A. the anode, because oxygen gas is reduced there. B. the anode, because the silver electrode is where reduction occurs. C. the cathode, because the silver electrode is where reduction occurs. D. the cathode, because the silver electrode is where oxidation occurs.
In an electrochemical cell, oxidation always occurs at the anode and reduction at the cathode. Oxidation is a process in which electrons are lost. The passage states that reduction occurs at the silver electrode, which means the silver electrode is the cathode. Since reduction occurs at the silver electrode, the Cd electrode is the anode. That Cd is the anode is verified by Equation 3, which shows that oxidation occurs there (i.e., Cd is oxidized). Thus, answer choice B is the best answer.
Which of the following best describes the motion of a negatively charged particle after it has been injected between the plates of a charged, parallel-plate capacitor? (Note: Assume that the area between the plates is a vacuum.) A. It moves with constant speed toward the positive plate. B. It moves with constant speed toward the negative plate. C. It accelerates toward the positive plate. D. It accelerates toward the negative plate.
Opposites attract, so the negatively charged particle will move toward the positive plate. Because there is a constant force qE on the particle, it will accelerate toward the positive plate. Thus, C is the best answer.
During Trial 5, the wire was heated from 293 K to 673 K while V was held constant at 28 V. How did the current through the circuit change during this time? A.It remained constant at 2 A. B.It remained constant at 4.6 A. C.It increased from 2 A to 4.6 A. D.It decreased from 4.6 A to 2 A.
Resistance is directly proportional to temperature so current decreases, based on Ohm's law. Since temperature increases by a factor of 673/293 ≅ 2.3, the resistance will increase by the same amount. From Ohm's Law, current decreases by a factor of 2.3 from 4.6 A to 2 A.
Which of the following graphs best illustrates the relationship between T and R? A. B. C. D.
Resistivity is linearly proportional to temperature. The graphic indicates that resistance increases with the increase in temperature.
How is the accuracy of the oxygen determination affected by the addition of a gas into the stream that is reduced by a reaction analogous to that of oxygen? A. Increased, because the smaller the amount of oxygen in the stream, the more effective is microanalysis B. Increased, because the larger the sample reduced, the less effect a small variation in measurement will have on results C. Decreased, because the partial pressure of oxygen will be decreased D. Decreased, because the method cannot distinguish oxygen from the added gas
Since oxygen is reduced during the procedure, any other gas that is reduced is indistinguishable from oxygen. Hence, the percent oxygen found by the experiment includes the added gas and is too high. Therefore, the accuracy of such a determination is decreased by the added gas. Thus, answer choice D is the best answer.
Why can the positive ions be considered to be fixed during the electrons' oscillations? A. The ions are bound together with strong nuclear forces. B. An ion is much more massive than an electron. C. The ions experience no force when the electron sea is displaced. D. Coulomb's law prohibits the motion of the ions.
Since the ions are thousands of times more massive than the electron, answer B is justified (the hydrogen ion is the lightest ion and is nearly 2000 times more massive than the electron). An ion with so much mass compared to an electron will not be able to respond quickly because of its inertia.
In the overall electrochemical reaction: A.nitrogen is oxidized at the anode, and hydrogen is reduced at the cathode. B.nitrogen is reduced at the cathode, and hydrogen is oxidized at the anode. C.nitrogen is reduced at the anode, and hydrogen is oxidized at the cathode. D.nitrogen is oxidized at the cathode, and hydrogen is reduced at the anode.
Solution: The correct answer is B. This is a General Chemistry question that falls under the content category "Electrochemistry and electrical circuits and their elements." The answer to this question is B because oxidation always occurs at the anode and reduction at the cathode of an electrochemical cell. Since nitrogen decreases in oxidation state during the reaction, it is reduced. Hydrogen, on the other hand, increases in oxidation state and is, therefore, oxidized. It is a Scientific Reasoning and Problem Solving question because you must reason using oxidation state assignment rules in order to draw a conclusion about the nature of a chemical reaction.
When the current in the micro-robot's circuit increases and the resistance of the circuit remains constant, the voltage of the circuit: A.decreases. B.increases. C.is constant. D.is zero.
Solution: The correct answer is B. This is a Physics question that falls under the content category "Electrochemistry and electrical circuits and their elements." The answer to this question is B because according to Ohm's law, current is equal to voltage divided by resistance. If current increases and resistance is constant, then voltage increases as well. It is a Scientific Reasoning and Problem Solving question because you are asked to determine and use scientific formulas to solve problems.
A 60-Ω resistor is connected in parallel with a 20-Ω resistor. What is the equivalent resistance of the combination? A.80 Ω B.40 Ω C.15 Ω D.3 Ω
Solution: The correct answer is C. This is a Physics question that falls under the content category "Electrochemistry and electrical circuits and their elements." The answer to this question is C because the equivalent resistance is given by the expression (1/(60) + 1/(20))-1 = 15 . It is a Scientific Reasoning and Problem Solving question because the question requires determining and using scientific formulas to solve problems.
A circuit similar to that in Figure 2 is set up. It has a potential of 2.0 V. Assume that the resistance in the circuit is negligible compared to that of the lightbulb. Approximately how much current passes through the lightbulb? A.0.5 A B.1.0 A C.2.0 A D.4.0 A
Solution: The correct answer is D. This is a Physics question that falls under the content category "Electrochemistry and electrical circuits and their elements." The answer to this question is D because according to Ohm's law, current is equal to voltage divided by resistance, hence 2.0 V/0.5 Ω = 4.0 A. It is a Scientific Reasoning and Problem Solving question because you are asked to determine and use scientific formulas to solve problems.
Which of the following energy conversions best describes what takes place in a battery-powered resistive circuit when the current is flowing? A.Electric to thermal to chemical B.Chemical to thermal to electric C.Electric to chemical to thermal D.Chemical to electric to thermal
Solution: The correct answer is D. This is a Physics question that falls under the content category "Electrochemistry and electrical circuits and their elements." The answer to this question is D because the chemical energy of the battery elements is used as electrical energy to set the charge carriers in motion through the resistor, where they experience drag from the crystal lattice of the resistive conductor and dissipate their energy as heat from the resistor. It is a Knowledge of Scientific Concepts and Principles question because the question requires identifying the relationships among closely related concepts.
A glass rod is rubbed with a silk scarf producing a charge of +3.2 × 10-9 C on the rod. (Recall that the magnitude of the proton and electron charges is 1.6 × 10-19 C.) The glass rod has: A.5.1 × 1011 protons added to it. B.5.1 × 1011 electrons removed from it. C.2.0 × 1010 protons added to it. D.2.0 × 1010 electrons removed from it.
Solution: The correct answer is D. This is a Physics question that falls under the content category "Electrochemistry and electrical circuits and their elements." The answer to this question is D because the number of charges in excess can be computed as +3.2 × 10 -9 C/1.6 × 10 -19 C = +2.0 × 10 10. This means that the rod has an excess of positive charge, created by removing a number of +2.0 × 10 10 electrons from the material, as it is not possible to add protons in a manner described in this question. It is a Scientific Reasoning and Problem Solving question because the question requires evaluating arguments about causes and consequences.
The three ions in the following figure are initially held fixed as shown. If Ion C alone were released, in which of the following directions would it begin to move? A.Toward the top B.Toward the bottom C.Toward the left D.Toward the right
Solution: The correct answer is D. This is a Physics question that falls under the content category "Electrochemistry and electrical circuits and their elements." The answer to this question is D because the released ion moves under the simultaneous effect of two forces: from ion A, toward the right and the top, and from ion B, toward the bottom and to the right. Because the forces depend inversely proportionally on the distances between the ions and directly proportionally on the product between their charges (which are all the same in absolute value), the resultant force is to the right because the top and bottom components cancel out. It is a Scientific Reasoning and Problem Solving question because the question requires analyzing and evaluating scientific explanations and predictions.
A small negatively charged particle is placed near a fixed positively charged particle (Q). Which of the following describes the motion of the negatively charged particle? A. It accelerates away from Q. B. It accelerates toward Q. C. It moves with constant speed away from Q. D. It moves with constant speed toward Q.
The Coulomb force between the negative and positive charges is attractive. That force accelerates the negatively-charged particle toward the positively charged particle. Choice B is the correct answer.
An experimental setup designed to measure the resistance of an unknown resistor R using two known resistors R1 and R2, the variable resistor R3, a voltage source, and a voltmeter is shown. Which relationship gives the value of R when R3 is adjusted so that the voltmeter reading is zero? R = R3 × R1/R2 R = R3 + R2 - R1 R = R3 - R2 + R1 R = R3 × R2/R1 _
The answer to this question is A, because when the voltmeter reading is zero, the voltage across R is equal to the voltage across R1 and from Ohm's law, IR = I1R1, where I and I1 are the currents through the resistors. Moreover, IR3 = I1R2. By taking the ratio of these two equations, it follows that R/R3 = R1/R2, which is equivalent to R = R3 × R1/R2. It is a Reasoning about the Design and Execution of Research question because you must reason about the features of this experimental setup and the association between the variables that enable the use of this particular design for its stated purpose.
The time dependence of the potassium current through a cell membrane channel subject to a constant 80-mV depolarization voltage is shown. What is the minimum electrical resistance of the ion channel during the time interval shown? A 120 kΩ B 160 kΩ C 200 MΩ D 240 MΩ
The answer to this question is C because the electrical resistance R of a conductor through which a current I passes when subject to a voltage V is given by Ohm's law: R = V/I = 80 mV/(400 × 10-12 A) = 200 MΩ. It is a Data-based and Statistical Reasoning question because you must use the data in the graph and determine the maximum value of the current, which corresponds to the minimum value of the resistance.
What is the magnitude of the electric field used in the MALDI-MS imaging device described in the passage? A 1 kV/m B 3 kV/m C 6 kV/m D 9 kV/m
The answer to this question is D because the intensity of a uniform electric field E is related to the voltage V and distance d over which it is applied as E = V/d = 4.5 kV/(0.5 m) = 9 kV/m. It is a Scientific Reasoning and Problem Solving question because you must determine and use the scientific formula E = V/d to solve the problem.
If the magnitude of a positive charge is tripled, what is the ratio of the original value of the electric field at a point to the new value of the electric field at that same point? A. 1:2 B. 1:3 C. 1:6 D. 1:9
The correct answer is B. Your previous answer is B. AAMC Standard Solution: The magnitude of the electric field E of a point charge is given by If q is tripled, E also will be tripled. Thus, B is the best answer.
An electron is ejected from the cathode by a photon with an energy slightly greater than the work function of the cathode. How will the final kinetic energy of the electron upon reaching the anode compare to its initial potential energy immediately after it has been ejected? A. It will be 2 times as large. B. It will be approximately equal. C. It will be 1/4 as large. D. It will be 0.
The correct answer is B. Your previous answer is B. AAMC Standard Solution: The near equality of the photon energy and the work function means that little initial kinetic energy will be left for the electron. This initial kinetic energy is small compared to the 50 eV it will gain from the potential difference between electrodes.
What information about an axon is required to calculate the current associated with an NCV pulse? A.Conductivity, resistivity, and length B.Potential, conductivity, and radius C.Potential, resistivity, and radius D.Potential, resistance per unit length, and length
The current associated with an NCV pulse can be calculated according to Ohm's law by dividing the potential change by the axon resistance which is the resistance per unit length divided by the length. Knowledge of conductivity and resistivity is irrelevant.
Which of the following occurs when electrons are ejected from the cathode? A. The voltage across the electrodes reverses polarity. B. The voltage difference between the electrodes increases. C. Current flows through the circuit. D. The total resistance of the circuit increases.
The electrons ejected from the cathode are replaced by electrons from the battery and anode. The only effect on the apparatus of electron ejection from the cathode is the current in the circuit.
One company sells a defibrillator for home use that uses a 9-volt DC battery. The battery is rated at 4.2 A•hr (amp•hour). Roughly how much charge can the battery deliver? A.4.2 C B.38 C C.15,000 C D.136,000 C
The magnitude is computed as an approximation of 4.2 × 9 = 37.8 ≈ 38. However, multiplying the corresponding units V × A•hr yields J, not C.
One function of the myelin sheath is to: A.insulate the axon from the surroundings. B.decrease the radius of the axon. C.produce Schwann cells. D.increase the capacitance of the axon.
The myelin sheath insulates the axon from the surroundings. This insulation acts to increase the rate of transmission of signals.
In Figure 1, the maximum electrical potential energy occurs at: A. A only. B. B only. C. C only. D. A and C only.
The potential energy of an oscillatory motion is ½kx2 where x is the displacement. Since the maximum displacement occurs at A and C, answer D is justified.
What is the magnitude of the electric field in the electrical discharge produced in the excimer laser tube? A.2.0 × 106 V/m B.4.0 × 105 V/m C.6.0 × 104 V/m D.8.0 × 103 V/m
The solution is A. The magnitude of the electric field produced by 8.0 kV across 4.0 mm is 8000 V/0.004 m = 2.0 × 106 V/m.
Of the events listed, which occurs first during action potential generation? A.Voltage-gated sodium channels open at the axon hillock. B.Hyperpolarization stimulates the opening of ligand-gated potassium channels. C.Graded potentials propagate along the axon. D.Calcium influx stimulates vesicle fusion and release of neurotransmitter.
The solution is A. When threshold is met at the axon hillock, voltage-gated sodium channels open, generating an action potentia
When a strip of Zn is placed in a beaker containing 0.1 M HCl, H2(g) evolves. If a strip of Al is placed in a beaker containing 0.1 M HCl, does H2(g) evolve? A.Yes; Al is reduced and H+(aq) is oxidized. B.Yes; Al is oxidized and H+(aq) is reduced. C.No; Al is reduced and Cl-(aq) is oxidized D.No; Al is oxidized and H2O(l) is produced.
This is a General Chemistry question that falls under the content category "Electrochemistry and electrical circuits and their elements." The answer to this question is B. Since a new solid forms when Al(s) is mixed with Zn2+(aq), it is reasonable to assume that Al(s) is more susceptible to oxidation than Zn(s). It is a Scientific Reasoning and Problem Solving question because you are asked to bring together theory and observations to draw a conclusion.
A circuit similar to that in Figure 2 is set up in which X = Pb, Xn+ = Pb2+, Y = Cu, and Ym+ = Cu2+. Will an oxidation-reduction reaction occur spontaneously? A.No; E°cell = -0.212. B.No; E°cell = +0.212. C.Yes; E°cell = -0.466. D.Yes; E°cell = +0.466.
This is a General Chemistry question that falls under the content category "Electrochemistry and electrical circuits and their elements." The answer to this question is D. A spontaneous reaction occurs when E° is greater than zero, and this occurs if the oxidation of Pb(s) is combined with the reduction of Cu2+(aq), resulting in a net E° of +0.466 V. It is a Scientific Reasoning and Problem Solving question because you are asked to determine and use a scientific formula to solve a problem after recognizing the relationship between E° and spontaneity.
A student can most effectively increase the current passing through the circuit in Figure 2 by doing which of the following? A.Using electrical wire with a smaller diameter B.Increasing the temperature of the electrical wire C. Decreasing the concentrations of Xn+(aq) and Ym+(aq) D.Replacing the lightbulb with one that has a resistance of 0.2 Ω
This is a Physics question that falls under the content category "Electrochemistry and electrical circuits and their elements." The answer to this question is D because according to Ohm's law, current is equal to voltage divided by resistance. In order to increase the current when the voltage fixed, the resistance must be decreased, such as by replacing the light-bulb with one that has a resistance of 0.2 Ω instead of 0.5 Ω. It is a Reasoning about the Design and Execution of Research question because you are asked to identify independent and dependent variables, which characterize experimental devices, and to reason about the appropriateness of the devices used to conduct research.
Another capacitor, identical to the original, is added in series to the circuit described in the passage. Compared to the original circuit, the equivalent capacitance of the new circuit is: A. 1/2 as great. B. the same. C. 2 times as great. D. 4 times as great.
When in series, capacitors C1 and C2 add by the inverse rule Therefore, if C1 = C2 = C, then Thus, A is the best answer. B.