Physics Exam 4
In a step-up transformer, there are _____ windings in the secondary coil than in the primary coil. The output voltage is _____ than the input voltage, and the output current is less than the input current.
more; greater
A transformer is used to change _____.
voltage
The energy of an individual photon is proportional to the wave frequency, and the proportionality constant is called Planck's constant = 6.63 × 10-34 J·s, represented by the letter _____.
h
The same amount of electric _____ can be delivered at any voltage, provided that the product of the current and voltage remains the same.
power
A(n) _____ can be made a better conductor of electricity by doping it with a small amount of a different kind of atom.
semiconductor
An electromagnetic wave is _____, meaning that the two disturbances, the electric field E and the magnetic field B, vary in the direction perpendicular to the direction of propagation.
transverse
How much does the maximum emf produced by a generator (a rotating coil) change if its magnetic field is halved?
It is decreased by a factor of 2.
The equations for an LC circuit are very similar to the equation for a block and ideal spring. The variable for the potential energy of the spring, Uspring is analogous to the electric energy in the _____.
capacitor
From very low frequency radio waves to very high frequency gamma rays, the _____ is the name given to the full range of possible electromagnetic waves.
electromagnetic spectrum
Although an electromagnetic wave does not require a medium through which to travel, the relationship to the propagation speed is the same as in mechanical waves, where the _____ of the wave times the wavelength equals the speed of propagation of the wave.
frequency
For an LC circuit, the _____ is equal to the ratio of the angular frequency over the product of the constants 2π.
frequency
Gamma-ray photons, x-ray photons, and short-wavelength, high-frequency ultraviolet photons are called _____ because _____.
ionizing radiation; such photons can break chemical bonds
The speed of radio waves in a vacuum _____.
is the same as the speed of microwaves in a vacuum
A beam of light is propagating in the x direction. The electric field vector E _____.
must oscillate in the yz plane
Gauss's law written as ΦB = 0 is _____. If ΦB were found to be non-zero it would be evidence of the existence of _____. No such observation has ever been confirmed.
one of Maxwell's equations; monopoles
Gauss's law written as ΦE = (1/ε0)qencl is _____. A hypothetical longitudinal electromagnetic wave (which carries no charge, so ΦE must be zero) violates Gauss's law. This leads to the conclusion that electromagnetic waves must be transverse, with the varying electric field vector _____ the direction of propagation.
one of Maxwell's equations; perpendicular to
The sinusoidal electromagnetic plane wave that propagates in the +x direction with E vector in the xy plane may be described by a set of wave functions Ey(x,t) = E0cos(kx - ωt + φ) and Bz(x,t) = B0cos(kx - ωt + φ). The _____ angle φ is given a value so that Ey and Bz at x = 0 and t = 0 are appropriate for a given plane wave.
phase
The energy of an electromagnetic wave comes in small packets called _____, whose properties help explain why certain kinds of electromagnetic waves can be harmful while others are not.
photons
The energy of an electromagnetic wave propagates as small, individual packets called _____, and the energy of each packet is proportional to the _____.
photons; wave frequency
A particularly simple kind of electromagnetic wave is the _____, with electric and magnetic fields that _____
sinusoidal plane wave; extend to infinity
Faraday's law holds even if there is no conducting material present to carry an induced current, in which case it may be stated in terms of _____ instead of induced emf to give _____ = -ΔΦB/Δt.
the circulating electric field; ΣE||Δℓ
Electromagnetic radiation transfers energy to atoms and molecules as _______.
an individual packet in a photon
The batteries that power a mobile device or a flashlight are sources of _____.
constant voltage
Faraday's law states that a time-varying _____ is induced in the secondary coil of a transformer, which means this coil acts as a voltage source.
emf
In a circuit, when the capacitor is charged and there is an electric field between the plates, no current is yet present, so there is not yet a magnetic field in the _____.
inductor
The electromagnetic _____ is the name given to the full range of possible electromagnetic waves of any wavelength, from very long radio waves to very short gamma rays.
spectrum
The energy of an individual photon is E = hf where f is the wave frequency and h is Planck's constant. Since a given molecule must absorb this energy in the form of a single photon, this explains why higher energy per photon _____ light causes a suntan or sunburn but light in the visible spectrum does not.
ultraviolet
The tuner knob on an FM radio moves the plates of an adjustable capacitor. This capacitor is in series with a 0.130-μH inductor and a net resistance of 755 Ω. The peak current induced in this circuit by a radio wave becomes large when the natural frequency of the circuit matches the carrier frequency of the radio wave. What is the frequency of the FM station that is tuned in when the capacitor in the radio is adjusted to 19.6 pF?
99.7
Ampere's law showed that electric charges in motion, such as current through a wire 𝒾through, would produce a(n) _____. Another scientist proposed that a changing electric field could have the same effect and added a term to Ampere's law to get ΣB||Δℓ = μ0(𝒾through + ε0ΔΦE/Δt), now known as _____.
circulating magnetic field; the Maxwell-Ampere law
The magnetic energy stored in an inductor can be thought of as stored in its magnetic field which is largely restricted to the space inside the solenoid. This motivates defining the energy per unit volume due to a magnetic field, or magnetic
energy density
The _____ of an electromagnetic wave propagates as small, individual packets called photons, and the energy of each photon is proportional to the _____. Please choose the correct answer from the following choices, and then select the submit answer button. Answer choices
energy; wave frequency
In a(n) _____ transformer no power is lost, however in reality, some power is lost as _____.
ideal ; heat
Bands within the full electromagnetic spectrum have been named, typically based on human applications or for historical reasons. Select the statement that is NOT correct about these bands.
The visible band lies between the ultraviolet, which has wavelengths longer than that of violet light, and the infrared, which has frequencies higher than that of red light.
The study of mechanical waves led to the relationship that the speed of propagation of the wave is equal to the frequency of the wave (f) times the wavelength (λ). Select the statement about the propagation speed of electromagnetic waves that is NOT correct.
Visible light travels at speed c in a vacuum, but by comparison harmful ultraviolet waves traveling through Earth's atmosphere propagate at a speed higher than c.
The speed of light, given the symbol c, has been determined experimentally to be 3.00 × 108 m/s (to 3 significant figures) in a vacuum. Select the statement that is NOT true. Please choose the correct answer from the following choices, and then select the submit answer button.
X rays propagate faster through glass than through a vacuum.
Faraday's law may be illustrated by placing a conducting loop in a changing magnetic field, but the law holds even if there is no conducting material present. Fundamentally what happens when the magnetic field changes is that _____ is produced.
a circulating electric field
The voltage of the capacitor is equal to the negative of the ratio of the _____ over the capacitance.
charge
One of Maxwell's equations is Gauss's law written as ΦE = (1/ε0)qencl. ΦE is written with a subscript to highlight that this equation is specifically addressing _____ across a closed surface.
electric flux
The fact that energy from the Sun arrives at the Earth in the form of electromagnetic waves indicates that_______
electromagnetic waves can travel in a vacuum
The fact that you can get a sunburn if you lie in direct sunlight is evidence that______.
electromagnetic waves carry energy
Light and other radiation are called _____ waves because they involve oscillating _______.
electromagnetic;
Light and other radiation are called _____ waves because they involve _____ electric and magnetic fields.
electromagnetic; oscillating
There is a broad variety of _____ waves, but unlike sound waves or waves in water, this type of wave involves _____ electric and magnetic fields and requires no physical medium through which to propagate.
electromagnetic; oscillating
An electromagnetic wave involves oscillating electric and magnetic _____, and the energy of an electromagnetic wave is carried in small packets called _____. The properties of electromagnetic waves are explained by the equations of electricity and magnetism. For example, the wave intensity depends on the _____ of the electric and magnetic fields.
fields; photons; amplitudes
X-rays differ from visible light in that they _______
have a different wavelength
Radiation damage in biological tissues occurs in generally___________.
higher frequencies in the EM spectrum
In an LC circuit, once the switch is closed a current is established in the circuit. The current will not suddenly increase but instead will gradually increase due to opposition from the _____.
inductor
In a transformer the coil that is connected to the _____ is called the primary coil, and the one that is the source of the _____ is called the secondary coil.
input voltage; output voltage
The energy associated with an electromagnetic wave depends on the energy density of _____, but these vary in space and time. Consider a magnetic field that varies sinusoidally with amplitude B0. The energy carried by the wave in its magnetic field depends not on the instantaneous value of B, but on the average magnetic energy density uaverage = ½B02/μ0.This type of average, dependent on the square of a sinusoidal function, is known as the _____.
its electric and magnetic fields; root mean square value
One of Maxwell's equations is Gauss's law written as ΦB = 0. ΦB is written with a subscript to highlight that this equation is specifically addressing _____ across a closed surface. Electric flux [["B" indicates a magnetic field.]]
magnetic flux
Although an electromagnetic wave does not require a medium through which to travel, the relationship to the propagation speed is the same as in mechanical waves, where the frequency of the wave (f) _____ (λ) equals the speed of propagation of the wave. Please choose the correct answer from the following choices, and then select the submit answer button. Answer choices
multiplied by the wavelength
The energy associated with an electromagnetic wave depends on the energy density of its electric and magnetic fields, but these fields vary sinusoidally with amplitudes E0 and B0. The energy carried by an electromagnetic wave thus depends on the average energy density uaverage. For the electric field, for example, uaverage is proportional to E02/2. An average that depends on the square of a sinusoidal function in this way is known as the _____ value.
root mean square
In order for electromagnetic waves to propagate
there needs to be no substance present; they can travel in a vacuum
The amplitude of the output voltage is different than that of the input voltage when going through a(n) _____.
transformer
Gauss's law written as ΦE = (1/ε0)qencl is one of Maxwell's equations. A hypothetical longitudinal electromagnetic wave (which carries no charge, so ΦE must be zero) violates Gauss's law. This leads to the conclusion that electromagnetic waves must be _____.
transverse
There are two disturbances in an electromagnetic wave, the electric field E and the magnetic field B, which vary in the direction perpendicular to the direction of propagation. This makes it a(n) _____ wave. Additionally, the E vector and the B vector are _____.
transverse; perpendicular to each other
For an LC circuit, the _____ the inductor is equal to the negative of the product of the inductance and the ratio of the change in current over the change in time.
voltage across
The sinusoidal electromagnetic plane wave that propagates in the +x direction with E vector in the xy plane may be described by a set of wave functions Ey(x,t) = E0cos(kx - ωt + φ) and Bz(x,t) = B0cos(kx - ωt + φ). The angular _____ k = 2π/λ is related to the wavelength.
wave number
Which of the following forms of electromagnetic radiation are generally hazardous to humans?
x-rays
The sinusoidal electromagnetic plane wave may be described by a set of sinusoidal wave functions of amplitude E0 and B0 for the electric and magnetic fields, respectively. In addition, E0 and B0 in a plane wave are _____ proportional to each other according to the equation _____.
directly; B0 = E0/c
James Clerk Maxwell had an important insight that led him to modify Ampere's law. The first term in the Maxwell-Ampere law, 𝒾through, accounts for moving charges, such as current flowing through a wire. Maxwell added the _____ current term, ε0ΔΦE/Δt, to account for contributions to circulating magnetic field due to a changing electric field.
displacement
Electromagnetic waves whose photons carry sufficient energy to break chemical bonds of molecules are called _____ radiation. Please choose the correct answer from the following choices, and then select the submit answer button. Answer choices
ionizing
One of Maxwell's equations is Faraday's law, ε = -ΔΦB/Δt. Faraday's law states that an emf is induced in a loop if the _____through that loop changes.
magnetic flux
For a power line it is best to use high voltage and low current because a long power line has a substantial _____ and some of the energy being carried by the current goes into heating the power line instead of being transmitted to the end user.
resistance
A(n) _____ uses two coils and a piece of magnetic material such as iron to raise or lower the voltage from an ac source.
transformer
Which of the following is a form of electromagnetic radiation which is generally not hazardous to humans?
Infrared
Human eyes can detect light from the sun and radio telescopes can receive radio waves from distant stars. Select the statement that is NOT true.
Radio waves can travel farther through space because they have a longer wavelength than visible light.
Electromagnetic waves of frequency 5.0 × 1014 Hz travel through space. These waves have wavelengths equal to _____.
600 nm
An electromagnetic plane wave of wavelength λ = 950 nanometers has an average energy density of uaverage = 1.67 × 10-8 joules per cubic meter. The energy carried per photon is _____ joules and the average photon density is _____ photons per cubic meter.
2.1 × 10-19; 8.0 × 1010
A parallel-plate capacitor has circular plates 2.50 centimeters in diameter. When the capacitor is being charged the electric field between the plate increases by 7.00 × 105 volts per meter in 0.015 seconds. What is the magnitude of the magnetic field induced around a loop 1.75 centimeters in diameter centered in the space between the capacitor plates?
2.3 × 10-12 T
Green light with wavelength 550 nanometers has energy equal to _____ joules per photon.
3.6 × 10-19
An electromagnetic plane wave has an intensity Saverage = 350 watts per square meter. The root mean square value of the electric field is _____ and the amplitude of the electric field is _____.
360 V/m; 510 V/m
The Earth is approximately 1.5 × 108 kilometers from the sun. About how long does it take for the light from the sun to reach the Earth?
500 seconds
A region of space has a uniform magnetic field that is initially 1.25 tesla but decreases to zero in 0.200 seconds. What is the magnitude of the induced electric field around a circular loop 5.00 centimeters in diameter oriented perpendicular to the magnetic field?
7.81 × 10-2 N/C
A parallel-plate capacitor has circular plates 2.50 centimeters in diameter. When the capacitor is being charged the electric field between the plate increases by 9.00 × 106 volts per meter in 0.025 seconds. What is the magnitude of the resulting displacement current through a loop 1.80 centimeters in diameter centered in the space between the capacitor plates? Please choose the correct answer from the following choices, and then select the submit answer button. Answer choices
8.1 × 10-7 A
