Dawn Of Modern Physics MCQs
a perfect absorber and a perfect emitter of radiation.
a perfect reflector of all incident radiation.
only a perfect absorber of radiation.
only a perfect emitter of radiation.
According to Planck's quantum theory, energy is radiated or absorbed:
continuously in the form of waves.
in discrete packets called quanta or photons.
only at very high temperatures.
only in the visible spectrum.
The energy of a single photon is directly proportional to its:
wavelength.
speed.
frequency.
intensity.
The photoelectric effect is the phenomenon where:
electrons are emitted from a heated metal.
a material gets charged due to pressure.
electrons are ejected from a metal by light.
light is emitted by an electric current.
In the photoelectric effect, the kinetic energy of the emitted photoelectrons depends on the:
intensity of the incident light.
frequency of the incident light.
duration of light exposure.
temperature of the metal surface.
The minimum frequency of incident light required to cause photoemission is called the:
critical frequency.
resonant frequency.
threshold frequency.
saturation frequency.
The Compton effect demonstrates that:
light behaves only as a wave.
photons have momentum.
electrons can be created from energy.
energy is not conserved in photon-electron collisions.
In the Compton effect, the scattered photon has a _______ wavelength compared to the incident photon.
Pair production is a process where a photon creates:
two electrons.
two positrons.
an electron and a proton.
an electron and a positron.
For pair production to occur, the minimum energy of the photon must be:
0.51 MeV
1.02 MeV
938 MeV
There is no minimum energy requirement.
The reverse process of pair production is known as:
Compton scattering.
Photoelectric effect.
Pair annihilation.
Nuclear fission.
The de Broglie hypothesis states that:
only photons have wave-particle duality.
all moving particles have an associated wave.
the energy of a particle is quantized.
particles can be in multiple places at once.
The de Broglie wavelength of a particle is given by the equation:
λ = hf
λ = mc²
λ = h/p
λ = pt/h
The wave nature of electrons was experimentally confirmed by:
J.J. Thomson's cathode ray experiment.
Einstein's photoelectric effect theory.
Millikan's oil drop experiment.
Davisson and Germer's electron diffraction.
Heisenberg's Uncertainty Principle states it is impossible to simultaneously know a particle's:
mass and energy.
charge and spin.
position and momentum.
velocity and acceleration.
If the uncertainty in the position of a particle is decreased, the uncertainty in its momentum:
decreases.
remains the same.
becomes zero.
increases.
The work function (φ) of a metal is:
the energy to move an electron within the metal.
the minimum energy to eject an electron from the surface.
the kinetic energy of an emitted photoelectron.
the energy of an incident photon.
A photocell is a device that converts:
heat energy into light energy.
light energy into electrical energy.
electrical energy into mechanical energy.
sound energy into electrical energy.
A radioactive nucleus has a half-life of 5000 years. What fraction of the original sample will be left after 20,000 years?
The binding energy of a Uranium-235 nucleus is 1786 MeV. What is the binding energy per nucleon?
1786 MeV
235 MeV
7.6 MeV
9.2 MeV
According to special relativity, the laws of physics are the same in all:
accelerating reference frames.
inertial reference frames.
gravitational fields.
rotating reference frames.
The second postulate of special relativity states that the speed of light in a vacuum:
depends on the source's speed.
depends on the observer's speed.
is constant for all inertial observers.
can be exceeded by massless particles.
Which of the following is a consequence of special relativity?
Time dilation
Conservation of mass
The existence of the ether.
Newton's law of universal gravitation.
The equation E=mc² expresses the:
relationship between energy and momentum.
quantization of energy.
mass-energy equivalence.
kinetic energy of a relativistic particle.
An electron microscope has higher resolution than an optical one because:
electrons are smaller than photons.
high-energy electrons have a very short de Broglie wavelength.
electrons have a negative charge.
the electron beam has greater intensity.
In a nuclear reaction, the mass defect is calculated to be 0.05 atomic mass units (amu). How much energy is released in Mega-electron Volts (MeV)?
931.5 MeV
46.575 MeV
18.63 MeV
0.05 MeV
In blackbody radiation, the 'ultraviolet catastrophe' was the failure of:
Planck's law at high frequencies.
the Stefan-Boltzmann law for total power.
Wien's law for the peak wavelength.
the classical Rayleigh-Jeans law at short wavelengths.
If light below the threshold frequency hits a metal, what happens if its intensity is increased?
Low energy photoelectrons are emitted.
High energy photoelectrons are emitted.
No photoelectrons are emitted.
The metal will heat up and emit electrons.
A radioactive isotope has a half-life of 15 hours. If a sample initially contains 800 grams of this isotope, how much will remain after 60 hours?
400 grams
200 grams
100 grams
50 grams
Which particle has the longest de Broglie wavelength when all are moving at the same speed?
A proton
An alpha particle
An electron
A neutron
The rest mass of a photon is:
equal to an electron's rest mass.
dependent on its energy.
zero.
infinite.
A fusion reaction combines two Deuterium nuclei (mass = 2.0141 amu each) to form a Helium-4 nucleus (mass = 4.0026 amu). Calculate the energy released in MeV.
4.0282 MeV
0.0256 MeV
23.8 MeV
4.0026 MeV
The half-life of Iodine-131 is 8 days. If a hospital receives a shipment of 20 mg, how much Iodine-131 will be left after 24 days?
Find the energy required to split a Carbon-12 nucleus into its constituent particles if its mass defect is 0.09894 amu.
12.0 MeV
92.16 MeV
0.09894 MeV
1118.3 MeV
In pair annihilation, an electron and a positron typically produce:
two photons in the same direction.
two photons in opposite directions.
a neutron.
a proton and an antiproton.
The stopping potential in a photoelectric experiment is a measure of the:
work function of the metal.
intensity of the incident light.
maximum K.E. of the photoelectrons.
number of emitted photoelectrons.
The concept of wave-particle duality applies to:
only light.
only subatomic particles.
only macroscopic objects.
all radiation and matter.
Wien's displacement law states the peak wavelength of blackbody radiation is:
proportional to absolute temperature.
inversely proportional to absolute temperature.
proportional to T⁴.
independent of temperature.
The Compton shift (Δλ) is maximum when the scattering angle is:
The existence of a threshold frequency in the photoelectric effect is best explained by:
the wave theory of light.
the particle nature of light (photons).
Heisenberg's uncertainty principle.
the de Broglie hypothesis.
The NAVSTAR Global Positioning System (GPS) must account for effects from:
only special relativity.
only general relativity.
both special and general relativity.
neither special nor general relativity.
Planck's constant (h) has units of:
Energy
Energy / Time (Power)
Energy × Time (Action)
Energy / Length
Which phenomenon provides evidence for the quantization of energy?
Diffraction of light
Blackbody radiation spectrum
Doppler effect
Refraction of light
Annihilation of matter results in the creation of:
new, heavier particles.
a vacuum.
pure energy (e.g., photons).
an equal amount of antimatter.
The energy of a photon is 3.3 x 10⁻¹⁹ J. What is its frequency? (h = 6.6 x 10⁻³⁴ J·s)
2.0 x 10¹⁴ Hz
0.5 x 10¹⁵ Hz
5.0 x 10¹² Hz
2.178 x 10⁻⁵² Hz
Relativistic mass increase is significant only at:
speeds near the speed of sound.
any speed greater than zero.
speeds near the speed of light.
the escape velocity of Earth.
The uncertainty principle implies that:
measurement devices are always flawed.
a particle's position and momentum are not simultaneously definite.
all physical quantities are quantized.
we can never be certain about any physical law.
If a red light and a blue light have the same intensity, which one has more photons per second?
The red light
The blue light
They have the same number of photons.
It cannot be determined.
The Davisson-Germer experiment involved the scattering of electrons from a:
gold foil.
double slit.
nickel crystal.
magnetic field.
A particle's de Broglie wavelength is 1 nm. If its momentum is doubled, its new wavelength will be:
Classical physics is a good approximation of modern physics at:
high speeds and small scales.
low speeds and large scales.
low speeds and small scales.
high speeds and large scales.
The photoelectric current is directly proportional to the:
frequency of incident light.
work function of the metal.
intensity of incident light.
stopping potential.
The 'h' in the equation E=hf stands for:
Heisenberg's constant.
Huygens' constant.
Hubble's constant.
Planck's constant.
The fact that the photoelectric effect is almost instantaneous supports:
the wave model of light.
the particle model of light.
the idea of an ether.
Newton's laws of motion.
An observer on a spaceship moving at 0.9c would observe time on Earth to be:
passing faster than their time.
passing slower than their time.
passing at the same rate.
stopped completely.
The energy-time uncertainty principle is given by:
ΔE Δt ≥ h/4π
ΔE / Δt ≥ h/4π
Δt / ΔE ≥ h/4π
ΔE Δt = 0
Modern physics began as an attempt to explain phenomena that:
could be seen with the naked eye.
involved large astronomical bodies.
were unexplainable by classical physics.
were discovered by ancient philosophers.
An observer moving at a relativistic speed with a light source will measure the speed of the emitted light as:
The Stefan-Boltzmann law relates the total power radiated by a black body to its:
peak wavelength.
T² (T is temperature).
T⁴ (T is temperature).
surface area.
In the photoelectric effect, if the frequency of the incident light is doubled, the max K.E. of photoelectrons will:
be doubled.
be halved.
increase, but less than double.
increase by more than double.
A radioactive isotope has a half-life of 15 hours. If a sample initially contains 800 grams of this isotope, how much will remain after 60 hours?
400 grams
200 grams
100 grams
50 grams
Which statement best describes the 'Compton Wavelength'?
De Broglie wavelength of a stationary electron.
Wavelength of a photon with energy equal to an electron's rest mass.
Minimum possible X-ray wavelength.
Longest possible wavelength for a photon.
Macroscopic objects in motion do not show observable wave properties because:
their speeds are too low.
their de Broglie wavelengths are too small.
their energy is not quantized.
their momentum is too small.
Pair production can only occur in the vicinity of a nucleus because it is needed to:
provide the required energy.
attract the newly formed positron.
conserve momentum.
provide a strong gravitational field.
According to the energy-time uncertainty principle, a virtual particle that exists for a very short time can have a:
very precise energy.
large uncertainty in energy.
zero energy.
precisely known position.
What is the decay constant for Carbon-14 if its half-life is 5730 years? (Use ln(2) = 0.693)
1.21 x 10⁻⁴ per year
8.27 x 10³ per year
3970 per year
0.693 per year
A sample has an initial activity of 1200 decays per minute. If its half-life is 4 minutes, what will its activity be after 12 minutes?
600 decays/min
300 decays/min
150 decays/min
75 decays/min
Calculate the energy released when 1 gram (0.001 kg) of matter is completely converted into energy. (Use speed of light, c = 3 x 10⁸ m/s)
3 x 10⁵ J
9 x 10¹³ J
3 x 10¹¹ J
9 x 10¹⁶ J
An astronaut ages slower traveling at near-light speed. From the astronaut's perspective:
their own clock is running slow.
the clock on Earth appears to run slow.
both their clock and the Earth clock run slow.
the clock on Earth appears to run fast.
What happens to the total energy radiated by a black body as its temperature is increased?
It decreases.
It remains constant.
It increases.
It becomes zero.
A metal has a work function of 2.0 eV. What is the maximum wavelength of light that can cause photoemission?
The momentum of a photon is given by:
An electron and a proton are accelerated through the same potential difference. Which has the shorter de Broglie wavelength?
The electron
The proton
They both have the same wavelength.
It cannot be determined.
The 'frame dragging' effect is a prediction of:
Special Relativity
General Relativity
Quantum Mechanics
Classical Mechanics
The intensity of a beam of light is a measure of:
the energy of individual photons.
the number of photons per unit area per second.
the speed of the photons.
the wavelength of the light.
A 1-meter stick on a spaceship moves at 0.8c. What length would an Earth observer measure?
1 meter
0.6 meters
1.67 meters
0.8 meters
Which of these is NOT a postulate of the special theory of relativity?
Laws of physics are the same in all inertial frames.
The speed of light in a vacuum is constant.
Mass-energy equivalence (E=mc²).
No inertial frame is preferred.
In an electron microscope, the 'lenses' used to focus the electron beam are:
convex glass lenses.
concave glass lenses.
magnetic fields.
gravitational fields.
A photon scatters off a stationary electron. Which of the following is impossible?
The photon's wavelength increases.
The electron gains kinetic energy.
The photon's wavelength decreases.
The photon is deflected from its path.
The resolution of a measurement is fundamentally limited by:
the skill of the experimenter.
the quality of the instruments.
the probe's wavelength.
the temperature of the room.
If you determine an electron's position with great accuracy, what is the consequence?
Its momentum becomes very certain.
Its momentum becomes very uncertain.
Its energy becomes zero.
Its charge becomes uncertain.
The total relativistic energy of a particle (E = γm₀c²) consists of:
only its kinetic energy.
only its rest mass energy.
its rest mass energy and its kinetic energy.
its potential energy and kinetic energy.
The idea that light is quantized (photons) was first proposed by Einstein to explain:
blackbody radiation.
the Compton effect.
the photoelectric effect.
the Davisson-Germer experiment.
A star appears yellowish-white. If its temperature were to double, it would likely appear:
reddish.
bluish-white.
darker.
unchanged in color.
Which of the following is conserved during pair annihilation?
Mass
Number of particles
Momentum
Kinetic energy
The 'relativity of simultaneity' means that:
all events happen at the same time.
simultaneous events in one frame may not be in another.
the speed of light is relative.
it's impossible to know if events are simultaneous.
The energy of a photon in a beam of light depends only on its:
intensity.
speed.
frequency.
direction.
How much energy in Joules is equivalent to a mass of 2 kilograms? (Use speed of light, c = 3 x 10⁸ m/s)
6 x 10⁸ J
1.8 x 10¹⁷ J
9 x 10¹⁶ J
2.0 J
A radioactive sample has a decay constant (lambda) of 0.0231 per day. What is its half-life in days? (Use ln(2) = 0.693)
231 days
100 days
30 days
69.3 days
In the Davisson-Germer experiment, the diffraction pattern was produced because:
electrons behaved like colliding particles.
the nickel crystal had a positive charge.
electron wavelength matched the crystal's atomic spacing.
the electrons were heated to a high temperature.
The Michelson-Morley experiment was designed to detect:
the wave nature of electrons.
the existence of the photon.
the luminiferous ether.
the curvature of spacetime.
A particle with zero rest mass must travel:
at a speed less than c.
at the speed of light (c).
at a speed greater than c.
at any speed, depending on its energy.
What is the relativistic momentum of a proton moving at 0.99c?
Slightly more than classical momentum.
About 7 times classical momentum.
Same as classical momentum.
Infinite.
If a particle's energy uncertainty is zero, what does this imply about the measurement time?
The time interval must be zero.
The time interval is very short.
The time interval must be infinite.
The time interval is uncertain.
The 'quantization' of a physical quantity means that it:
is conserved in all interactions.
can only take on discrete values.
is relative to the observer's frame.
is always a very small number.
Why can pair production not be caused by a visible light photon?
Visible light photons have no mass.
Visible light photons do not carry momentum.
A visible light photon has too little energy.
Visible light is not an electromagnetic wave.
The phenomenon of wave-particle duality was first introduced for:
Electrons by de Broglie
Light by Einstein
Protons by Rutherford
Atoms by Bohr
According to special relativity, which of the following is an invariant quantity?
Length
Time interval
Velocity
The spacetime interval
The failure of classical physics to explain blackbody radiation is known as:
The Photoelectric Problem.
The Compton Crisis.
The Ultraviolet Catastrophe.
The Relativistic Anomaly.
If the stopping potential for a certain metal is 1.5 V, what is the max K.E. of the photoelectrons?
1.5 J
1.5 eV
2.4 x 10⁻¹⁹ V
Cannot be determined.
In the Compton effect, the greatest change in wavelength occurs when the photon is scattered by:
A particle is confined to a box. If the size of the box is decreased, the uncertainty in its momentum will:
decrease.
remain the same.
increase.
become zero.
The 'twin paradox' is resolved by considering that:
special relativity is incorrect.
one twin undergoes acceleration.
time is absolute.
the speed of light changes for one twin.
What is the rest mass energy of an electron? (mₑ = 9.11 x 10⁻³¹ kg)
0.511 MeV
1.02 MeV
938 MeV
Zero
The spectrum of radiation from a black body is:
discrete, with sharp spectral lines.
a single peak at one wavelength.
a continuous spectrum dependent on temperature.
uniform across all wavelengths.
If an incident photon in a Compton scattering event has energy E, the scattered photon will have energy E' such that:
A photocell works on the principle of:
Compton Effect
Pair Production
Photoelectric Effect
Uncertainty Principle
Calculate the binding energy per nucleon for Helium-4, which has a total binding energy of 28.3 MeV.
28.3 MeV
14.15 MeV
7.075 MeV
4.0 MeV
An ancient wooden artifact has a Carbon-14 activity of 25% that of a modern sample. What is the age of the artifact? (Half-life of C-14 = 5730 years)
5730 years
11460 years
2865 years
17190 years
What is the radius of a Germanium nucleus (A=70) if the empirical radius constant is 1.2 x 10⁻¹⁵ m? (Use the cube root of 70 is approx. 4.12)
1.2 x 10⁻¹⁵ m
8.4 x 10⁻¹⁴ m
4.12 x 10⁻¹⁵ m
4.94 x 10⁻¹⁵ m
According to de Broglie, the wave associated with a particle is a:
light wave.
sound wave.
probability wave.
gravitational wave.
The equation m = m₀ / √(1 - v²/c²) describes:
Length contraction
Time dilation
Relativistic mass
Mass-energy equivalence
Which experiment provided the most direct evidence for the wave nature of electrons?
Millikan's oil drop experiment
The photoelectric effect
Rutherford's gold foil experiment
The Davisson-Germer experiment
The work function of a material depends on:
the frequency of the incident light.
the intensity of the incident light.
the properties of the material.
the temperature of the material.
A sample initially contains 6.4 x 10²⁰ radioactive atoms. If its half-life is 100 years, how many atoms will have decayed after 500 years?
0.2 x 10²⁰ atoms
3.2 x 10²⁰ atoms
6.2 x 10²⁰ atoms
5.4 x 10²⁰ atoms
The activity of a sample is 8000 Bq. After 6 hours, its activity is 1000 Bq. What is its half-life?
6 hours
3 hours
2 hours
1 hour
An electron and a positron, each with a rest mass energy of 0.511 MeV, annihilate each other. What is the total energy of the photons produced?
0.511 MeV
1.022 MeV
0.255 MeV
2.044 MeV
In order to observe an object, the wavelength of the probing radiation must be:
much larger than the object.
equal to or smaller than the object.
exactly equal to the speed of light.
infinite.
The 'Dawn of Modern Physics' refers to the period when:
Newton developed his laws of motion.
Maxwell unified electricity and magnetism.
classical theories failed to explain new phenomena.
the first nuclear reactor was built.
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