Modern Physics
Q. What is the relationship between the stopping potential and the maximum kinetic energy of the emitted electrons in the photoelectric effect?
A.
Stopping potential is directly proportional to the work function
B.
Stopping potential is inversely proportional to the maximum kinetic energy
C.
Stopping potential is equal to the maximum kinetic energy
D.
Stopping potential has no relation to the photoelectric effect
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Solution
The stopping potential (V) is related to the maximum kinetic energy (KE) of the emitted electrons by the equation KE = eV, where e is the charge of the electron.
Correct Answer: C — Stopping potential is equal to the maximum kinetic energy
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Q. What is the relationship between the stopping potential and the maximum kinetic energy of emitted electrons in the photoelectric effect?
A.
Stopping potential is directly proportional to the work function
B.
Stopping potential is directly proportional to the maximum kinetic energy
C.
Stopping potential is inversely proportional to the frequency
D.
Stopping potential has no relation to kinetic energy
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Solution
The stopping potential (V) is directly proportional to the maximum kinetic energy (KE) of the emitted electrons, given by the equation KE = eV, where e is the charge of the electron.
Correct Answer: B — Stopping potential is directly proportional to the maximum kinetic energy
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Q. What is the relationship between the wavelength of light and the energy of the emitted electrons in the photoelectric effect?
A.
Energy is directly proportional to wavelength
B.
Energy is inversely proportional to wavelength
C.
Energy is independent of wavelength
D.
Energy is proportional to the square of wavelength
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Solution
The energy of the emitted electrons is inversely proportional to the wavelength of the incident light, as given by E = hc/λ.
Correct Answer: B — Energy is inversely proportional to wavelength
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Q. What is the relationship between the work function and the threshold frequency?
A.
Φ = hν₀
B.
Φ = ν₀/h
C.
Φ = h/ν₀
D.
Φ = ν₀²/h
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Solution
The work function (Φ) is directly proportional to the threshold frequency (ν₀) as Φ = hν₀.
Correct Answer: A — Φ = hν₀
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Q. What is the role of a demodulator in a communication system?
A.
To amplify the received signal
B.
To convert the modulated signal back to its original form
C.
To filter out noise from the signal
D.
To encode the signal for transmission
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Solution
A demodulator's primary function is to convert the modulated signal back to its original form so that the information can be retrieved.
Correct Answer: B — To convert the modulated signal back to its original form
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Q. What is the role of a diode in a circuit?
A.
Resistor
B.
Capacitor
C.
Current regulator
D.
Current rectifier
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Solution
A diode acts as a current rectifier, allowing current to flow in one direction while blocking it in the opposite direction.
Correct Answer: D — Current rectifier
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Q. What is the role of a diode in a semiconductor circuit?
A.
Amplification
B.
Rectification
C.
Oscillation
D.
Capacitance
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Solution
A diode is primarily used for rectification, allowing current to flow in one direction only.
Correct Answer: B — Rectification
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Q. What is the role of a moderator in a nuclear reactor?
A.
To absorb neutrons
B.
To slow down neutrons
C.
To increase the temperature
D.
To shield radiation
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Solution
The role of a moderator in a nuclear reactor is to slow down neutrons, making them more likely to induce fission in the fuel.
Correct Answer: B — To slow down neutrons
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Q. What is the role of a p-n junction in a semiconductor device?
A.
To increase resistance
B.
To create a depletion region
C.
To enhance thermal conductivity
D.
To reduce current flow
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Solution
A p-n junction creates a depletion region which is essential for the operation of diodes and transistors.
Correct Answer: B — To create a depletion region
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Q. What is the role of a semiconductor in a transistor?
A.
To store charge
B.
To amplify current
C.
To insulate
D.
To generate heat
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Solution
In a transistor, the semiconductor material is used to amplify current, allowing small input signals to control larger output signals.
Correct Answer: B — To amplify current
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Q. What is the role of a transistor in electronic circuits?
A.
Switching
B.
Amplification
C.
Signal modulation
D.
All of the above
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Solution
Transistors can perform multiple functions including switching, amplification, and signal modulation.
Correct Answer: D — All of the above
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Q. What is the role of a transponder in satellite communication?
A.
To amplify the received signal
B.
To convert signals from one frequency to another
C.
To modulate the signal for transmission
D.
To demodulate the received signal
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Solution
A transponder receives signals at one frequency, amplifies them, and then converts them to another frequency for transmission back to Earth.
Correct Answer: B — To convert signals from one frequency to another
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Q. What is the role of temperature in the behavior of semiconductors?
A.
It has no effect
B.
It decreases conductivity
C.
It increases the number of charge carriers
D.
It only affects p-type semiconductors
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Solution
Temperature increases the number of charge carriers in semiconductors, thus increasing their conductivity.
Correct Answer: C — It increases the number of charge carriers
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Q. What is the significance of the Heisenberg Uncertainty Principle in atomic structure?
A.
It defines the size of the nucleus
B.
It limits the precision of measuring position and momentum
C.
It explains electron configurations
D.
It describes the stability of atoms
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Solution
The Heisenberg Uncertainty Principle states that it is impossible to simultaneously know the exact position and momentum of a particle, which is fundamental in quantum mechanics.
Correct Answer: B — It limits the precision of measuring position and momentum
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Q. What is the significance of the Heisenberg Uncertainty Principle?
A.
It defines the energy levels of electrons
B.
It states that position and momentum cannot be simultaneously known
C.
It describes the behavior of light
D.
It explains the stability of atomic nuclei
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Solution
The Heisenberg Uncertainty Principle states that the position and momentum of a particle cannot be simultaneously known with arbitrary precision.
Correct Answer: B — It states that position and momentum cannot be simultaneously known
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Q. What is the significance of the photoelectric effect in modern physics?
A.
It explains the wave nature of light
B.
It supports the theory of relativity
C.
It led to the development of quantum mechanics
D.
It has no significance
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Solution
The photoelectric effect was crucial in the development of quantum mechanics, as it provided evidence for the quantization of energy.
Correct Answer: C — It led to the development of quantum mechanics
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Q. What is the term for the energy required to remove an electron from an atom in the gas phase?
A.
Ionization energy
B.
Electron affinity
C.
Electronegativity
D.
Electrostatic energy
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Solution
Ionization energy is defined as the energy required to remove an electron from an atom in the gas phase.
Correct Answer: A — Ionization energy
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Q. What is the threshold frequency for a metal if the work function is 4.5 eV?
A.
5.4 x 10^14 Hz
B.
6.0 x 10^14 Hz
C.
7.2 x 10^14 Hz
D.
8.0 x 10^14 Hz
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Solution
Threshold frequency (ν₀) = Work function (Φ) / h = 4.5 eV / (4.14 x 10^-15 eV·s) = 5.4 x 10^14 Hz.
Correct Answer: A — 5.4 x 10^14 Hz
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Q. What is the total number of orbitals in the n=2 energy level?
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Solution
The total number of orbitals in an energy level is given by n^2. For n=2, it is 2^2 = 4.
Correct Answer: B — 4
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Q. What is the total number of orbitals in the n=4 energy level?
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Solution
The total number of orbitals in an energy level is given by n^2. For n=4, it is 4^2 = 16.
Correct Answer: C — 16
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Q. What is the truth value of the expression A AND (B OR C) when A = 1, B = 0, and C = 1?
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Solution
First, evaluate B OR C, which is 0 OR 1 = 1. Then, A AND 1 = 1 AND 1 = 1.
Correct Answer: B — 1
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Q. What is the truth value of the expression A AND (B OR C) when A = 1, B = 0, C = 1?
A.
0
B.
1
C.
2
D.
Undefined
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Solution
B OR C = 0 OR 1 = 1. Then, A AND 1 = 1 AND 1 = 1.
Correct Answer: B — 1
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Q. What is the typical band gap of germanium?
A.
0.66 eV
B.
1.1 eV
C.
1.5 eV
D.
2.0 eV
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Solution
The typical band gap of germanium is approximately 0.66 eV.
Correct Answer: A — 0.66 eV
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Q. What is the typical range of energy band gaps for semiconductors?
A.
0.1 - 0.5 eV
B.
0.5 - 1.5 eV
C.
1.5 - 3.0 eV
D.
3.0 - 5.0 eV
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Solution
The typical range of energy band gaps for semiconductors is between 0.5 eV and 1.5 eV.
Correct Answer: B — 0.5 - 1.5 eV
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Q. What is the typical range of the energy band gap for semiconductors?
A.
0.1 - 0.5 eV
B.
0.5 - 2.5 eV
C.
2.5 - 5 eV
D.
5 - 10 eV
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Solution
The typical range of the energy band gap for semiconductors is between 0.5 eV and 2.5 eV.
Correct Answer: B — 0.5 - 2.5 eV
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Q. What is the uncertainty in position if the uncertainty in momentum of a particle is 1.0 x 10^-24 kg m/s?
A.
1.0 x 10^-10 m
B.
6.63 x 10^-10 m
C.
1.0 x 10^-34 m
D.
6.63 x 10^-34 m
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Solution
Using Heisenberg's uncertainty principle, ΔxΔp ≥ ħ/2, we find Δx ≥ ħ/(2Δp) = (1.055 x 10^-34)/(2 x 1.0 x 10^-24) = 5.27 x 10^-11 m.
Correct Answer: D — 6.63 x 10^-34 m
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Q. What is the uncertainty principle formulated by Heisenberg?
A.
ΔxΔp ≥ ħ/2
B.
ΔEΔt ≥ ħ
C.
ΔxΔE ≥ ħ
D.
ΔpΔt ≥ ħ
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Solution
The uncertainty principle states that the product of the uncertainties in position (Δx) and momentum (Δp) is greater than or equal to ħ/2.
Correct Answer: A — ΔxΔp ≥ ħ/2
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Q. What is the uncertainty principle in quantum mechanics?
A.
ΔxΔp ≥ ħ/2
B.
ΔEΔt ≥ ħ/2
C.
Both A and B
D.
None of the above
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Solution
The uncertainty principle states that ΔxΔp ≥ ħ/2 and ΔEΔt ≥ ħ/2, where ħ is the reduced Planck's constant.
Correct Answer: C — Both A and B
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Q. What is the wavelength of an electron accelerated through a potential difference of 100 V? (mass of electron = 9.11 x 10^-31 kg)
A.
1.22 x 10^-10 m
B.
1.23 x 10^-9 m
C.
1.24 x 10^-11 m
D.
1.25 x 10^-12 m
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Solution
The wavelength λ = h/p = h/sqrt(2meV) = (6.63 x 10^-34)/sqrt(2 * 9.11 x 10^-31 * 100) = 1.22 x 10^-10 m.
Correct Answer: A — 1.22 x 10^-10 m
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Q. What is the wavelength of light emitted when an electron transitions from n=3 to n=2 in a hydrogen atom?
A.
410 nm
B.
656 nm
C.
486 nm
D.
434 nm
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Solution
Using the Rydberg formula, the wavelength for the transition from n=3 to n=2 is approximately 434 nm.
Correct Answer: D — 434 nm
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