Q&A Hero

Q: Magnetic dipole X is fixed.Dipole Y is placed in the position indicated and isfree to move. The first thing dipole Y will do is: A) move toward X but not rotate B) move away from X but not rotate C) move toward X and rotate D) move away from X and rotate E) rotate but not move toward or away from X

Q: Magnetic dipole X is fixed and dipole Y is free to move. Dipole Y will initially: A) move toward X but not rotate B) move away from X but not rotate C) move toward X and rotate D) move away from X and rotate E) rotate but not translate

Q: A small bar magnet is suspended horizontally by a string. When placed in a uniform horizontal magnetic field, it will: A) translate in the direction of B) translate in the opposite direction of C) rotate so as to be at right angles to D) rotate so as to be vertical E) none of the above

Q: A bar magnet is broken in half. Each half is broken in half again, etc. The observation is that each piece has both a north and south pole. This is usually explained by: A) Ampere's theory that all magnetic phenomena result from electric currents B) our inability to divide the magnet into small enough pieces C) Coulomb's law D) Lenz' law E) conservation of charge

Q: A bar magnet is placed vertically with its S pole up and its N pole down. The field at its center is: A) zero B) down C) up D) horizontal E) slightly below the horizontal

Q: The polarity of an unmarked magnet can be determined using: A) a charged glass rod B) a compass C) an electroscope D) another unmarked magnet E) iron filings

Q: A positively charged ion, due to a cosmic ray, is headed through Earth's atmosphere toward the center of Earth. Due to Earth's magnetic field, the ion will be deflected: A) south B) north C) west D) east E) not at all since it is a charge and not a pole

Q: Of the following places one would expect that the horizontal component of the Earth's magnetic field to be largest in: A) Maine B) Florida C) Maryland D) New York E) Iowa

Q: The magnetic field of Earth is roughly the same as that of a magnetic dipole with a dipole moment of about: A) 1017J/T B) 1019J/T C) 1021J/T D) 1023J/T E) 1025J/T

Q: Maxwell's equations, along with an appropriate symmetry argument, can be used to calculate: A) the electric force on a given charge B) the magnetic force on a given moving charge C) the flux of a given electric field D) the flux of a given magnetic field E) none of these

Q: Which of the following equations, along with a symmetry argument, can be used to calculate the magnetic field between the plates of a charging parallel plate capacitor with circular plates? A) B) C) D) E) none of these

Q: Which of the following equations, along with a symmetry argument, can be used to calculate the electric field produced by a uniform time-varying magnetic field? A) B) C) D) E) none of these

Q: Which of the following equations, along with a symmetry argument, can be used to calculate the magnetic field produced by a uniform time-varying electric field? A) B) C) D) E) none of these

Q: Which of the following equations can be used to show that magnetic field lines form closed loops? A) B) C) D) E) none of these

Q: Which of the following equations can be used, along with a symmetry argument, to calculate the magnetic field of a long straight wire carrying current? A) B) C) D) E) none of these

Q: Which of the following equations can be used, along with a symmetry argument, to calculate the electric field of a point charge? A) B) C) D) E) none of these

Q: One of the crucial facts upon which the Maxwell equations are based is: A) the numerical value of the electron charge B) charge is quantized C) the numerical value of the charge/mass ratio of the electron D) there are three types of magnetic materials E) none of the above

Q: Consider the four Maxwell equations: I. II. III. IV. Which of these must be modified if magnetic poles are discovered? A) only I B) only II C) only II and III D) only III and IV E) only II, III, IV

Q: A circular parallel-plate capacitor whose plates have a radius of 25 cm is being charged with a current of 1.3 A. What is the magnetic field 11 cm from the center of the plates? A) 4.6 x 10-7T B) 1.0 x 10-6T C) 2.4 x 10-6T D) 3.1 x 10-6T E) 6.2 x 10-6T

Q: Displacement current exists in the region between the plates of a parallel plate capacitor if: A) the capacitor leaks charge across the plates B) the capacitor is being discharged C) the capacitor is fully charged D) the capacitor is fully discharged E) none of the above are true

Q: A current of 1 A is used to charge a parallel plate capacitor with square plates. If the area of each plate is 0.6 m2the displacement current through a 0.3 m2area wholly between the capacitor plates and parallel to them is: A) 2 A B) 1 A C) 0.7 A D) 0.5 A E) 0.25 A

Q: Displacement current exists wherever there is: A) moving charge B) a magnetic field C) a changing magnetic field D) an electric field E) a changing electric field

Q: Displacement current is:

Q: A 1-­F capacitor is connected to an emf that is increasing uniformly with time at a rate of 100 V/s. The displacement current between the plates is:A) 0 AB) 1 x10-8AC) 1 x10-6AD) 1 x10-4AE) 100 A

Q: A 1.2-m radius cylindrical region contains a uniform electric field along the cylinder axis. It is increasing uniformly with time. To obtain a total displacement current of 2.0 x10-9 A through a cross section of the region, the magnitude of the electric field should change at a rate of:A) 5.0 V/msB) 12 V/msC) 37 V/msD) 50 V/msE) 4.0 x107 V/ms

Q: Two of Maxwell's equations contain a path integral on the left side and an area integral on the right. Suppose the area is the surface of a piece of paper at which you are looking and is chosen to point toward you. Then, the path integral is: A) clockwise around the circumference of the paper B) counterclockwise around the circumference of the paper C) from left to right D) from right to left E) from top to bottom

Q: Two of Maxwell's equations contain a path integral on the left side and an area integral on the right. The directions of the infinitesimal path element and infinitesimal area element are: A) always in the same direction B) always in opposite directions C) always perpendicular to each other D) never perpendicular to each other E) none of the above

Q: Two of Maxwell's equations contain an integral over a closed surface. For them the infinitesimal vector area is always: A) tangent to the surface B) perpendicular to the surface and pointing outward C) perpendicular to the surface and pointing inward D) tangent to a field line E) perpendicular to a field line

Q: Two of Maxwell's equations contain a path integral on the left side and an area integral on the right. For them: A) the path must pierce the area B) the path must be well-separated from the area C) the path must be along a field line and the area must be perpendicular to the field line D) the path must be the boundary of the area E) the path must lie in the area, away from its boundary

Q: One of the Maxwell equations begins with .... The osymbol in the integral sign means:A) the same as the subscript in B) integrate clockwise around the pathC) integrate counterclockwise around the pathD) integrate around a closed pathE) integrate over a closed surface

Q: One of the Maxwell equations begins with .... The osymbol in the integral sign means:A) the same as the subscript in B) integrate clockwise around the pathC) integrate counterclockwise around the pathD) integrate around a closed pathE) integrate over a closed surface

Q: One of the Maxwell equations begins with .... The symbol means: A) an infinitesimal displacement of a charge B) an infinitesimal displacement of a magnetic pole C) an infinitesimal inductance D) an infinitesimal surface area E) none of the above

Q: An electron is on the zaxis moving toward the xyplane but it has not reached that plane yet. At that instant: A) there is only a true current through the xyplane B) there is only a displacement current through the xyplane C) there are both true and displacement currents through the xyplane D) there is neither a true nor a displacement current through the xyplane E) none of the above are true

Q: Suppose you are looking into one end of a long cylindrical tube in which there is a uniform electric field, pointing away from you. If the magnitude of the field is decreasing with time the field lines of the induced magnetic field are: A) circles B) ellipses C) straight lines parallel to the electric field D) straight lines perpendicular to the electric field E) none of the above

Q: Suppose you are looking into one end of a long cylindrical tube in which there is a uniform electric field, pointing away from you. If the magnitude of the field is decreasing with time the direction of the induced magnetic field is: A) toward you B) away from you C) clockwise D) counterclockwise E) to your right

Q: The diagram shows one plate of a parallel-plate capacitor from within the capacitor. The plate is circular and has radius R. The dashed circles are four integration paths have radii of r1= R/4, r2= R/2, r3=3 R/2, and r4= 2R. Rank the paths according to the magnitude of around the paths during the discharging of the capacitor, least to greatest. A) 1, 2 and 3 tie, then 4 B) 1, 2, 3, 4 C) 1, then 2 and 4 tie, then 3 D) 4, 3, 1, 2 E) 3, then 2 and 4 tie, then 1

Q: An electric field exists in the cylindrical region shown and is parallel to the cylinder axis. The magnitude of the field might vary with time according to any of the four graphs shown. Rank the four variations according to the magnitudes of the magnetic field induced at the edge of the region, least to greatest. A) 2, 4, 3, 1 B) 1, 3, 4, 2 C) 4, 3, 2, 1 D) 4, 3, 1, 2 E) 2, 1, 3, 4

Q: A sinusoidal emf is connected to a parallel plate capacitor. The magnetic field between the plates is: A) zero B) constant C) sinusoidal and its amplitude does not depend on the frequency of the source D) sinusoidal and its amplitude is proportional to the frequency of the source E) sinusoidal and its amplitude is inversely proportional to the frequency of the source

Q: A 0.70-m radius cylindrical region contains a uniform electric field that is parallel to the axis and is increasing at the rate 5.0 x1012V/m.s. The magnetic field at a point 1.2 m from the axis has a magnitude of:A) 0 TB) 7.0 x10-6TC) 1.1 x10-5TD) 2.3 x10-5TE) 2.8 x10-5T

Q: A 0.70-m radius cylindrical region contains a uniform electric field that is parallel to the axis and is increasing at the rate 5.0x1012V/m.s. The magnetic field at a point 0.25 m from the axis has a magnitude of:A) 0 TB) 7.0 x10-6TC) 2.8x10-5TD) 5.4 x10-5TE) 7.0 x10-5T

Q: A cylindrical region contains a uniform electric field that is parallel to the axis and is changing with time. If ris the distance from the cylinder axis the magnitude of the magnetic field outside the region is: A) zero B) proportional to 1/r C) proportional to r2 D) proportional to 1/r2 E) proportional to r

Q: A cylindrical region contains a uniform electric field that is along the cylinder axis and is changing with time. If ris the distance from the cylinder axis the magnitude of the magnetic field within the region is: A) uniform B) proportional to 1/r C) proportional to r2 D) proportional to 1/r2 E) proportional to r

Q: A magnetic field exists between the plates of a capacitor: A) always B) never C) when the capacitor is fully charged D) while the capacitor is being charged E) only when the capacitor is starting to be charged

Q: A 1-A current is used to charge a parallel plate capacitor. A large square piece of paper is placed between the plates and parallel to them so it sticks out on all sides. The value of the integral around the perimeter of the paper is:

Q: Four closed surfaces are shown, each with circular top and bottom faces and curved sides. The areas Atopand Abotof the top and bottom faces and the magnitudes Btopand Bbotof the uniform magnetic fields through the top and bottom faces are given. The fields are perpendicular to the faces and are either inward or outward. Rank the surfaces according to the magnitude of the magnetic flux through the curved sides, least to greatest. A) 1, 2, 3, 4 B) 3, 4, 1, 2 C) 1, 2, 4, 3 D) 4, 3, 2, 1 E) 2, 1, 4, 3

Q: Gauss' law for magnetism, , tells us: A) the net charge in any given volume B) that the line integral of a magnetic field around any closed loop must vanish C) the magnetic field of a current element D) that magnetic monopoles do not exist E) charges must be moving to produce magnetic fields

Q: According to Gauss' law for magnetism, magnetic field lines: A) form closed loops B) start at south poles and end at north poles C) start at north poles and end at south poles D) start at both north and south poles and end at infinity E) do not exist

Q: A magnetic field parallel to the xaxis with a magnitude that decreases with increasing xbut does not change with yand zis impossible according to: A) Faraday's law B) Ampere's law C) Gauss' law for electricity D) Gauss' law for magnetism E) Newton's second law

Q: The statement that magnetic field lines form closed loops is a direct consequence of: A) Faraday's law B) Ampere's law C) Gauss' law for electricity D) Gauss' law for magnetism E) the Lorentz force

Q: Gauss' law for magnetism:A) can be used to find due to given currents provided there is enough symmetryB) is false because there are no magnetic polesC) can be used with open surfaces because there are no magnetic polesD) contradicts Faraday's law because one says B= 0 and the other says = -dB/dtE) none of the above

Q: A source with an impedance of 100 is connected to the primary coil of a transformer and a resistance Ris connected to the secondary coil. If the transformer has 500 turns in its primary coil and 100 turns in its secondary coil the greatest power will be dissipated in the resistor if R=A) 0 B) 0.25 C) 4.0 D) 20E) 100

Q: In an ideal 1:8 step-down transformer, the primary power is 10 kW and the secondary current is 25 A. The primary voltage is: A) 25,600 V B) 3200 V C) 400 V D) 50 V E) 6.25 V

Q: The primary of a 3:1 step-up transformer is connected to a source and the secondary is connected to a resistor R. The power dissipated by Rin this situation is P. If Ris connected directly to the source it will dissipate a power of: A) P/9 B) P/3 C) P D) 3P E) 9P

Q: The primary of an ideal transformer has 100 turns and the secondary has 600 turns. Then: A) the power in the primary circuit is less than that in the secondary circuit B) the currents in the two circuits are the same C) the voltages in the two circuits are the same D) the primary current is six times the secondary current E) the frequency in the secondary circuit is six times that in the primary circuit

Q: The resistance of the primary coil of a well-designed, 1:10 step-down transformer is 1. With the secondary circuit open, the primary is connected to a 12 V ac generator. The primary current is:A) essentially zeroB) about 12 AC) about 120 AD) depends on the actual number of turns in the primary coilE) depends on the core material

Q: A step-down transformer is used to: A) increase the power B) decrease the power C) increase the voltage D) decrease the voltage E) change ac to dc

Q: A generator supplies 100 V to the primary coil of a transformer. The primary has 50 turns and the secondary has 500 turns. The secondary voltage is: A) 1000 V B) 500 V C) 250 V D) 100 V E) 10 V

Q: A power transmission line carries 400A of current at a voltage of 765 kV. If the line has a resistance of 29 , what is the rate at which energy is being dissipated in 800 km of line?A) 0 WB) 3.7 kWC) 310 kWD) 3.7 MWE) 310 MW

Q: For a power transmission line, the transmission should be at low current and high voltage because: A) this is the least dangerous to electrical workers B) this gives the least dose of electromagnetic radiation to the public C) this minimizes transmission losses D) low current and high voltage is easier to transform than high current and low voltage E) household appliances run at low current and high voltage

Q: The core of a transformer is made in a laminated form to: A) facilitate easy assembly B) reduce i2Rlosses in the coils C) increase the magnetic flux D) save weight E) prevent eddy currents

Q: Iron, rather than copper, is used in the core of transformers because iron: A) can withstand a higher temperature B) has a greater resistivity C) has a very high permeability D) makes a good permanent magnet E) insulates the primary from the secondary

Q: The main reason that alternating current replaced direct current for general use is: A) ac generators do not need slip rings B) ac voltages may be conveniently transformed C) electric clocks do not work on dc D) a given ac current does not heat a power line as much as the same dc current E) ac minimizes magnetic effects

Q: In order to maximize the rate at which energy is supplied to a resistive load, the power factor of an RLC circuit should be as close as possible to: A) 0 B) 0.5 C) 1 D) infinity E) cannot tell without knowing R, L, C, and the driving frequency

Q: A series circuit consists of a 15- resistor, a 25-mH inductor, and a 35-­F capacitor. If the frequency is 100 Hz the power factor is:A) 0B) 0.20C) 0.45D) 0.65E) 1.0

Q: The average power supplied to the circuit shown passes through a maximum when which one of the following is increased continuously from a very low to a very high value? A) source emf B) R C) C D) source frequencyf E) none of these

Q: The rms value of an ac current is: A) its peak value B) its average value C) that steady current that produces the same rate of heating in a resistor D) that steady current that will charge a battery at the same rate E) zero

Q: An RLCcircuit has a sinusoidal source of emf. The average rate at which the source supplies energy is 5 nW. This must also be: A) the average rate at which energy is stored in the capacitor B) the average rate at which energy is stored in the inductor C) the average rate at which energy is dissipated in the resistor D) twice the average rate at which energy is stored in the capacitor E) three times the average rate at which energy is stored in the inductor

Q: In a sinusoidally driven series RLCcircuit the current lags the applied emf. The rate at which energy is dissipated in the resistor can be increased by: A) decreasing the capacitance and making no other changes B) increasing the capacitance and making no other changes C) increasing the inductance and making no other changes D) increasing the driving frequency and making no other changes E) decreasing the amplitude of the driving emf and making no other changes

Q: In a series RLCcircuit the rms value of the generator emf is and the rms value of the current is i. The current lags the emf by . The average power supplied by the generator is given by:

Q: A sinusoidal voltage V(t) has an rms value of 100 V. Its maximum value is: A) 70.7 V B) 100 V C) 141 V D) 200 V E) 707 V

Q: The rms value of a sinusoidal voltage is , where V0is the amplitude. What is the rms value of its fully rectified wave? Recall thatA) B) C) D) E)

Q: The units of the power factor are: A) ohm B) watt C) radian D) ohm1/2 E) none of these

Q: The ideal meters shown read rms current and voltage. The average power delivered to the load is: A) definitely not equal to VI B) perhaps more than VI C) possibly equal to VIeven if the load contains an inductor and a capacitor D) definitely less than VI E) zero as is the average of any sine wave

Q: An RLCseries circuit, connected to a source , is at resonance. Then:A) the voltage across Ris zeroB) the voltage across Requals the applied voltageC) the voltage across Cis zeroD) the voltage across Lequals the applied voltageE) the applied voltage and current differ in phase by 90°

Q: In a sinusoidally driven series RLCcircuit, the inductive resistance is XL= 200 , the capacitive reactance is XC= 100 , and the resistance is R= 50 . The current and applied emf would be in phase if:A) the resistance is increased to 100, with no other changesB) the resistance is increased to 200 , with no other changesC) the inductance is reduced to zero, with no other changesD) the capacitance is doubled, with no other changesE) the capacitance is halved, with no other changes

Q: An RLCseries circuit is driven by a sinusoidal emf with angular frequency . If is increased without changing the amplitude of the emf, the current amplitude increases. If Lis the inductance, Cis the capacitance, and Ris the resistance, this means that:

Q: An RCseries circuit is connected to an emf source having angular frequency . The current:

Q: A series RLcircuit is connected to an emf source of angular frequency . The current:

Q: In a purely inductive circuit, the current lags the voltage by: A) 0 (they are in phase) B) one-fourth of a cycle C) one-half of a cycle D) three-fourths of a cycle E) one cycle

Q: In a purely resistive circuit the current: A) leads the voltage by 1/4 cycle B) leads the voltage by 1/2 cycle C) lags the voltage by 1/4 cycle D) lags the voltage by 1/2 cycle E) is in phase with the voltage