Q&A Hero

Q: A sinusoidal electromagnetic wave has an electric field whose rms value is 100 V/m. What is the instantaneous rate Sof energy flow for this wave?

Q: An electromagnetic wave is transporting energy in the negative ydirection. At one point and one instant the magnetic field is in the positive xdirection. The electric field at that point and instant is: A) positive ydirection B) negative ydirection C) positive zdirection D) negative zdirection E) negative xdirection

Q: At a certain point and a certain time the electric field of an electromagnetic wave is in the negative zdirection and the magnetic field is in the positive ydirection. Which of the following statements is true? A) Energy is being transported in the positive xdirection but half a cycle later, when the electric field is in the opposite direction, it will be transported in the negative xdirection. B) Energy is being transported in the positive xdirection and half a cycle later, when the electric field is in the opposite direction, it will still be transported in the positive xdirection. C) Energy is being transported in the negative xdirection but half a cycle later, when the electric field is in the opposite direction, it will be transported in the positive xdirection. D) Energy is being transported in the negative xdirection and half a cycle later, when the electric field is in the opposite direction, it will still be transported in the negative xdirection. E) None of the above is true.

Q: For an electromagnetic wave the direction of the vector gives: A) the direction of the electric field B) the direction of the magnetic field C) the direction of wave propagation D) the direction of the electromagnetic force on a proton E) the direction of the emf induced by the wave

Q: The rate of energy transport of an electromagnetic wave per unit area is given by: A) the vector B) the Poynting vector C) the Poynting vector divided by the area D) the Poynting vector divided by time E) the Poynting vector multiplied by time

Q: The time averaged energy in a sinusoidal electromagnetic wave is: A) overwhelmingly electrical B) slightly more electrical than magnetic C) equally divided between the electric and magnetic fields D) slightly more magnetic than electrical E) overwhelmingly magnetic

Q: The dimensions of are: A) J/m2 B) J/s C) W/s D) W/m2 E) J/m3

Q: If the amplitude of the electric field in a plane electromagnetic wave is 100 V/m then the amplitude of the magnetic field is:

Q: If the electric field in a plane electromagnetic wave is along the yaxis and its magnitude is given by in SI units, then the magnetic field is along the zaxis and its magnitude is given by:

Q: If the magnetic field in a plane electromagnetic wave is along the y axis and its magnitude is given by in SI units, then the electric field is along the z axis and its magnitude is given by

Q: In a plane electromagnetic wave in vacuum, the ratio E/Bof the amplitudes in SI units of the two fields is: A) the speed of light B) an increasing function of frequency C) a decreasing function of frequency D) E) 1/

Q: Maxwell's equations predict that the speed of electromagnetic waves in free space is given by:

Q: The product has the same units as:A) (velocity)2B) (velocity)1/2C) 1/velocityD) 1/velocity2E) 1/velocity1/2

Q: The electric field for a plane electromagnetic wave traveling in the +ydirection is shown. Consider a point where is in the +zdirection. The field is: A) in the +xdirection and in phase with the field B) in the "xdirection and in phase with the field C) in the +xdirection and 1/4 wave out of phase with the field D) in the +zdirection and in phase with the field E) in the +zdirection and 1/4 wave out of phase with the field

Q: If the electric field in a plane electromagnetic wave is given by Emsin[(3 x106m-1x)- t], the value of is:A) 0.01 rad/sB) 10 rad/sC) 100 rad/sD) 9 x1014rad/sE) 9 x1016rad/s

Q: Radio waves of wavelength 300 m have a frequency of:A) 10-6kHzB) 108 kHzC) 500 kHzD) 1 MHzE) 9 MHz

Q: Radio waves of wavelength 3 cm have a frequency of: A) 1 MHz B) 9 MHz C) 100 MHz D) 900 MHz E) 10,000 MHz

Q: Visible light has a frequency of about:A) 5x1018HzB) 5 x1016HzC) 5 x1014HzD) 5x1012HzE) 5 x1010Hz

Q: The time for a radar signal to travel to the Moon and back, a one-way distance of about 3.8 x108m, is:A) 1.3 sB) 2.5 sC) 8 sD) 8 minE) 1 x106s

Q: The sun is about 1.5 x1011m away. The time for light to travel this distance is about:A) 4.5 x1019sB) 8 sC) 8 minD) 8 hrE) 8 yr

Q: Which of the following types of electromagnetic radiation travels at the greatest speed in vacuum? A) Radio waves B) Visible light C) X rays D) Gamma rays E) All of these travel at the same speed

Q: The speed of light in vacuum is about:A) 1100 ft/sB) 93 x106mi/sC) 6 x1023m/sD) 3x1010cm/sE) 186,000 mph

Q: Maxwell's equations predict that the speed of light in free space is: A) an increasing function of frequency B) a decreasing function of frequency C) independent of frequency D) a function of the distance from the source E) a function of the size of the source

Q: Which of the following is NOT true for electromagnetic waves? A) they consist of changing electric and magnetic fields B) they travel at different speeds in vacuum, depending on their frequency C) they transport energy D) they transport momentum E) they can be reflected

Q: A transmitter consists of an LC circuit with an inductance of 15 H and a capacitance of 23 pF. What is the wavelength of the electromagnetic waves it emits? A) 29 mm B) 65 mm C) 5.6 m D) 35 m E) 220 m

Q: Radio waves differ from visible light waves in that radio waves: A) travel slower B) have a higher frequency C) travel faster D) have a lower frequency E) require a material medium

Q: Of the following human eyes are most sensitive to: A) red light B) violet light C) blue light D) green light E) none of these (they are equally sensitive to all colors)

Q: The order of increasing wavelength for blue (b), green (g), red (r), and yellow (y) light is: A) r, y, g, b B) r, g, y, b C) g, y, b, r D) b, g, y, r E) b, y, g, r

Q: Consider radio waves (r), visible light (v), infrared (i), X rays (x), and ultraviolet (u). In order of increasing frequency, they are: A) r, v, i, x, u B) r, i, v, u, x C) i, r, v, u, x D) x, u, v, i, r E) r, i, v, x, u

Q: Select the correct statement: A) ultraviolet light has a longer wavelength than infrared B) blue light has a higher frequency than X rays C) radio waves have a higher frequency than gamma rays D) gamma rays have a higher frequency than infrared waves E) electrons are a type of electromagnetic wave

Q: An electromagnetic wave is traveling in the positive xdirection with its electric field along the zaxis and its magnetic field along the yaxis. The fields are related by:

Q: An electromagnetic wave is generated by: A) any moving charge B) any accelerating charge C) only a charge with changing acceleration D) only a charge moving in a circle E) only a charge moving in a straight line

Q: The theoretical upper limit for the frequency of electromagnetic waves is: A) just slightly greater than that of red light B) just slightly less than that of blue light C) the greatest x-ray frequency D) none of the above (there is no upper limit) E) none of the above (but there is an upper limit)

Q: Why do polarizing sunglasses work to reduce glare? A) They don"t; this is just a marketing ploy B) They reduce the amount of light entering your eyes C) Light reflected from horizontal surfaces tends to be horizontally polarized, so the sunglasses' vertical polarization cuts the glare D) Light reflected from horizontal surfaces tends to be vertically polarized, so the sunglasses' horizontal polarization cuts the glare E) Light reflected from horizontal surfaces tends to be horizontally polarized, so the sunglasses' horizontal polarization cuts the glare

Q: For a beam of light in air (n= 1) reflecting off glass (n= 1.5), what is Brewster's angle? A) 34 B) 42 C) 45 D) 48 E) 56

Q: A ray of light in water (index n1) is incident on its surface (with air) at the critical angle. Some oil (index n2) is now floated on the water. The angle between the ray in the oil and the normal is:A) sin-1(1.00)B) sin-1(1/n1)C) sin-1(1/n2)D) sin-1(n1/n2)E) sin-1(n2/n1)

Q: If nwater= 1.33 and nglass= 1.50, then total internal reflection at an interface between this glass and water: A) occurs whenever the light goes from glass to water B) occurs whenever the light goes from water to glass C) may occur when the light goes from glass to water D) may occur when the light goes from water to glass E) can never occur at this interface

Q: The illustration shows total internal reflection taking place in a piece of glass. The index of refraction of this glass:A) is at least 2.0B) is at most 2.0C) is at least 1.15D) is at most 1.15E) cannot be calculated from the given data

Q: The index of refraction of a certain glass is 1.50. The sine of the critical angle for total internal reflection at a glass-air interface is: A) 0.50 B) 0.67 C) 0.75 D) 1.00 E) 1.50

Q: The index of refraction of benzene is 1.80. The critical angle for total internal reflection, at a benzene-air interface, is about:A) 56°B) 47°C) 34°D) 22°E) 18°

Q: The diagram shows total internal reflection. Which of the following statements is NOT true? A) angle AON is the angle of incidence B) angle AON = angle BON C) angle AON must be the critical angle D) the speed of light in medium II is greater than that in medium I E) if angle AON were increased, there would still be total internal reflection

Q: The critical angle for total internal reflection at a diamond-air interface is 25°. Suppose light is incident at an angle of with the normal. Total internal reflection will occur if the incident medium is:

Q: The rectangular metal tank shown is filled with an unknown liquid. The observer, whose eye is level with the top of the tank, can just see corner E. The index of refraction of this liquid is: A) 1.75 B) 1.67 C) 1.50 D) 1.33 E) 1.25

Q: Of the three chief kinds of magnetic materials (diamagnetic, paramagnetic, and ferromagnetic) which are used to make permanent magnets? A) only diamagnetic B) only ferromagnetic C) only paramagnetic D) only paramagnetic and ferromagnetic E) all three

Q: An unmagnetized steel bar is placed inside a solenoid. As the current in the solenoid is slowly increased from zero to some large value, the magnetization of the bar: A) increases proportionally with the current B) remains zero for awhile and then increases linearly with any further increase in current C) increases with increasing current at first but later is much less affected by it D) is unaffected by the current E) increases quadratically with the current

Q: Because ferromagnets exhibit hysteresis, the magnetization: A) can never be in the same direction as an applied field B) may not vanish when an applied field is reduced to zero C) can never vanish D) is proportional to any applied magnetic field E) is always opposite to the direction of any applied magnetic field

Q: The behavior of ferromagnetic domains in an applied magnetic field gives rise to: A) hysteresis B) ferromagnetism C) the Curie law D) a lowering of the Curie temperature E) Gauss' law for magnetism

Q: Magnetization vectors in neighboring ferromagnetic domains are: A) always in opposite directions B) always in the same direction C) always in different directions D) sometimes in different directions and sometimes in the same direction E) sometimes in opposite directions and sometimes in the same direction

Q: Ferromagnetism is closely associated with: A) the tendency of electron dipole moments to align with an applied magnetic field B) the tendency of electron dipole moments to align opposite to an applied magnetic field C) the tendency of electron dipole moments to change magnitude in an applied magnetic field D) the tendency of electron dipole moments to align with each other E) the force exerted by electron dipole moments on each other

Q: When a permanent magnet is strongly heated: A) nothing happens B) it becomes an induced magnet C) it loses its magnetism D) its magnetism increases E) its polarity reverses

Q: The soft iron core in the solenoid shown is removable. Then: A) the current will be larger without the core B) the current will be larger with the core C) one must do work to remove the core D) the circuit will do work in expelling the core E) the stored energy is the same with or without the core

Q: A paramagnetic substance is placed in a weak magnetic field and its absolute temperature Tis increased. As a result, its magnetization: A) increases in proportion to T B) increases in proportion to T2 C) remains the same D) decreases in proportion to 1/T E) decreases in proportion to 1/T2

Q: Magnetization is: A) the current density in an object B) the charge density of moving charges in an object C) the magnetic dipole moment of an object D) the magnetic dipole moment per unit volume of an object E) the magnetic field per unit volume produced by an object

Q: A magnetic field is applied to a paramagnetic substance. In the interior the magnetic field produced by the magnetic dipoles of the substance is: A) greater than and in the opposite direction B) less than and in the opposite direction C) greater than and in the same direction D) less than and in the same direction E) the same as

Q: The diagram shows two small paramagnetic spheres, one near each end of a bar magnet. Which of the following statements is true? A) The force on 1 is toward the magnet and the force on 2 is away from the magnet B) The force on 1 is away from the magnet and the force on 2 is away from the magnet C) The forces on 1 and 2 are both toward the magnet D) The forces on 1 and 2 are both away from the magnet E) The magnet does not exert a force on either sphere

Q: Paramagnetism is closely associated with: A) the tendency of electron dipole moments to align with an applied magnetic field B) the tendency of electron dipole moments to align opposite to an applied magnetic field C) the exchange force between electrons D) the force exerted by electron dipole moments on each other E) the torque exerted by electron dipole moments on each other

Q: A paramagnetic substance, in an external magnetic field, is thermally isolated. The field is then removed. As a result: A) the magnetic energy of the magnetic dipoles decreases B) the temperature of the substance increases C) the magnetization decreases, but only slightly D) the magnetization reverses direction E) none of the above

Q: The units of magnetization are:A) ampereB) ampere.meterC) ampere.meter2D) ampere/meterE) ampere/meter2

Q: The diagram shows two small diamagnetic spheres, one near each end of a bar magnet. Which of the following statements is true? A) The force on 1 is toward the magnet and the force on 2 is away from the magnet B) The force on 1 is away from the magnet and the force on 2 is away from the magnet C) The forces on 1 and 2 are both toward the magnet D) The forces on 1 and 2 are both away from the magnet E) The magnet does not exert a force on either sphere

Q: A magnetic field is applied to a diamagnetic substance. In the interior the magnetic field produced by the magnetic dipoles of the substance is: A) greater than and in the opposite direction B) less than and in the opposite direction C) greater than and in the same direction D) less than and in the same direction E) the same as

Q: Lenz' law can explain: A) paramagnetism only B) diamagnetism only C) ferromagnetism only D) only two of the three types of magnetism E) all three of the types of magnetism

Q: An electron in a hydrogen atom moves in a circle of radius 1.1 x 10-10m at a speed of about 1.6 x 106m/s. What is the magneticdipole moment of this electron due to its orbital motion? A) 9.3 x 10-24J/T B) 1.4 x 10-23J/T C) 1.9 x 10-23J/T D) 2.8 x 10-23J/T E) 3.5 x 10-23J/T

Q: What are the possible allowed values of the orbital magnetic quantum number of the electron?A) 0 onlyB) 0, 1 onlyC) any half-odd integerD) 0, 1, 2, …, up to the maximum value for that orbitE) It depends on the external magnetic field.

Q: The intrinsic magnetic dipole moments of protons and neutrons are much less than that of an electron because: A) their masses are greater B) their angular momenta are much less C) their angular momenta are much greater D) their charges are much less E) their radii are much less

Q: If an electron has an orbital angular momentum with magnitude Lthe magnitude of the orbital contribution to its magnetic dipole moment is given by: A) eL/m B) eL/2m C) 2eL/m D) mL/e E) mL/2

Q: If is the orbital angular momentum of an electron, the magnetic dipole moment associated with its orbital motion: A) is in the direction of and has magnitude proportional to L B) is opposite to the direction of and has magnitude proportional to L C) is in the direction of and has magnitude proportional to L2 D) is opposite to the direction of and has magnitude proportional to L2 E) does not depend on

Q: The diagram shows the spin angular momentum vectors of two electrons and two protons in the same external magnetic field. The field points upward in the diagram. Rank the situations according to the potential energy, least to greatest. A) 1 and 3 tie, then 2 and 4 tie B) 2 and 3 tie, then 1 and 4 tie C) 1 and 2 tie, then 3 and 4 tie D) 3 and 4 tie, then 1 and 2 tie E) all tie

Q: The magnitude of the Bohr magneton is about:A) 10-15J/TB) 10-19J/TC) 10-23J/TD) 10-27J/TE) 10-31J/T

Q: The magnetic dipole moment of an atomic electron is typically: A) much less than a Bohr magneton B) a few Bohr magnetons C) much greater than a Bohr magneton D) much greater or much less than a Bohr magneton, depending on the atom E) not related to the value of the Bohr magneton

Q: If an electron has zero orbital angular momentum, the magnitude of its magnetic dipole moment equals: A) zero B) half the Bohr magneton C) a Bohr magneton D) twice a Bohr magneton E) none of these

Q: What are the possible allowed values of the spin magnetic quantum number msof the electron? A) +1/2 only B) 1/2 C) any half-odd integer D) any integer E) It depends on the external magnetic field.

Q: Which of the following statements is correct? A) The spin angular momentum of the electron can be directly observed, but the spin magnetic dipole moment cannot be. B) The spin angular momentum of the electron cannot be directly observed, but the spin magnetic dipole moment can be. C) Both the spin angular momentum and the spin magnetic dipole moment of the electron can be directly observed. D) Neither the spin angular momentum nor the spin magnetic dipole moment of the electron can be directly observed. E) Although both the spin angular momentum and the spin magnetic dipole moment can be defined theoretically, neither has any physical meaning at all.

Q: The spin magnetic dipole moment of an electron: A) is in the same direction as the spin angular momentum B) is zero C) has a magnitude that depends on the orbital angular momentum D) has a magnitude that depends on the applied magnetic field E) none of the above

Q: The magnetic properties of materials stem chiefly from: A) particles with north poles B) particles with south poles C) motions of protons within nuclei D) proton spin angular momentum E) electron magnetic dipole moments

Q: The molecular theory of magnetism can explain each of the following EXCEPT: A) a N pole attracts a S pole B) stroking an iron bar with a magnet will magnetize the bar C) when a bar magnet is broken in two, each piece is a bar magnet D) heating tends to destroy magnetization E) hammering tends to destroy magnetization

Q: An electron traveling with speed varound a circle of radius ris equivalent to a current of:

Q: Which of the following statements is correct? A) The declination of the Earth's magnetic field is the angle between a horizontal plane and the direction of the field. B) The declination of the Earth's magnetic field is the angle between a vertical plane and the direction of the field. C) The inclination of the Earth's magnetic field is the angle between a horizontal plane and the direction of the field. D) The inclination of the Earth's magnetic field is the angle between the horizontal component of the field direction and the direction to geographic north. E) Inclination and declination mean the same thing.

Q: Which of the following statements about the Earth's magnetic field is correct? A) The Earth's magnetic field is approximately that of a dipole, and the north magnetic pole is in the northern hemisphere. B) The Earth's magnetic field is approximately that of a dipole, and the north magnetic pole is in the southern hemisphere. C) The Earth's magnetic field is approximately that of a monopole, and the north magnetic pole is in the northern hemisphere. D) The Earth's magnetic field is approximately that of a monopole, and the north magnetic pole is in the southern hemisphere. E) The Earth's magnetic field is approximately that of a quadrupole, and the north magnetic pole is in the eastern hemisphere.

Q: The magnetic field lines due to an ordinary bar magnet: A) form closed curves B) cross one another near the poles C) are more numerous near the N pole than near the S pole D) leave the S pole, loop around the outside of the magnet, and enter the N pole E) none of the above

Q: The potential energy of a magnetic dipole in an external magnetic field is least when: A) the dipole moment is parallel to the field B) the dipole moment is antiparallel to the field C) the dipole moment is perpendicular to the field D) none of the above (the same energy is associated with all orientations) E) none of the above (no energy is associated with the dipole-field interaction)