Modern Physics
Q. What is the band gap energy of a typical semiconductor?
A.
0 eV
B.
1-3 eV
C.
5 eV
D.
10 eV
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Solution
Typical semiconductors have a band gap energy in the range of 1-3 eV.
Correct Answer: B — 1-3 eV
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Q. What is the band gap energy of a typical silicon semiconductor?
A.
0.1 eV
B.
1.1 eV
C.
2.0 eV
D.
3.5 eV
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Solution
Silicon has a band gap energy of approximately 1.1 eV, which is suitable for many electronic applications.
Correct Answer: B — 1.1 eV
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Q. What is the band gap energy of silicon at room temperature?
A.
0.1 eV
B.
1.1 eV
C.
2.0 eV
D.
3.5 eV
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Solution
The band gap energy of silicon at room temperature is approximately 1.1 eV.
Correct Answer: B — 1.1 eV
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Q. What is the bandwidth of a signal that has a frequency range from 300 Hz to 3 kHz?
A.
2.7 kHz
B.
3.3 kHz
C.
2.4 kHz
D.
3.0 kHz
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Solution
Bandwidth = f_max - f_min = 3000 Hz - 300 Hz = 2700 Hz or 2.7 kHz.
Correct Answer: A — 2.7 kHz
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Q. What is the bandwidth of a signal that occupies a frequency range from 1 kHz to 3 kHz?
A.
1 kHz
B.
2 kHz
C.
3 kHz
D.
4 kHz
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Solution
Bandwidth = f_max - f_min = 3 kHz - 1 kHz = 2 kHz.
Correct Answer: B — 2 kHz
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Q. What is the bandwidth of a signal that occupies a frequency range from 300 Hz to 3 kHz?
A.
2.7 kHz
B.
3.3 kHz
C.
2.4 kHz
D.
3.0 kHz
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Solution
Bandwidth = f_max - f_min = 3000 Hz - 300 Hz = 2700 Hz = 2.7 kHz.
Correct Answer: A — 2.7 kHz
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Q. What is the binding energy of a nucleus?
A.
Energy required to remove a nucleon
B.
Energy released during nuclear fusion
C.
Energy required to split the nucleus
D.
Energy required to form the nucleus from its constituents
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Solution
The binding energy of a nucleus is the energy required to form the nucleus from its constituent protons and neutrons.
Correct Answer: D — Energy required to form the nucleus from its constituents
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Q. What is the binding energy per nucleon for a stable nucleus?
A.
Less than 1 MeV
B.
About 8 MeV
C.
More than 10 MeV
D.
Zero
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Solution
Stable nuclei typically have a binding energy per nucleon around 8 MeV.
Correct Answer: B — About 8 MeV
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Q. What is the critical mass in nuclear fission?
A.
Mass required for a chain reaction
B.
Mass of a single nucleus
C.
Mass of the entire reactor
D.
Mass of fuel rods
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Solution
Critical mass is the minimum mass of fissile material needed to maintain a sustained nuclear chain reaction.
Correct Answer: A — Mass required for a chain reaction
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Q. What is the critical mass in nuclear physics?
A.
Mass required for a stable nucleus
B.
Mass required to sustain a nuclear chain reaction
C.
Mass of a neutron
D.
Mass of a proton
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Solution
Critical mass is the minimum mass of fissile material needed to maintain a nuclear chain reaction.
Correct Answer: B — Mass required to sustain a nuclear chain reaction
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Q. What is the de Broglie wavelength of an electron moving with a velocity of 1.5 x 10^6 m/s? (mass of electron = 9.11 x 10^-31 kg)
A.
4.86 x 10^-10 m
B.
2.42 x 10^-10 m
C.
1.33 x 10^-10 m
D.
6.63 x 10^-10 m
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Solution
The de Broglie wavelength λ = h/p = h/(mv). Using h = 6.63 x 10^-34 J.s, we find λ = 6.63 x 10^-34 / (9.11 x 10^-31 * 1.5 x 10^6) = 2.42 x 10^-10 m.
Correct Answer: B — 2.42 x 10^-10 m
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Q. What is the effect of doping a semiconductor with acceptor impurities?
A.
Increases electron concentration
B.
Increases hole concentration
C.
Decreases conductivity
D.
No effect
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Solution
Doping with acceptor impurities creates holes, thus increasing the hole concentration in the semiconductor.
Correct Answer: B — Increases hole concentration
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Q. What is the effect of doping a semiconductor with donor atoms?
A.
Increases hole concentration
B.
Increases electron concentration
C.
Decreases conductivity
D.
Creates a depletion region
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Solution
Doping a semiconductor with donor atoms increases the electron concentration, making it n-type.
Correct Answer: B — Increases electron concentration
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Q. What is the effect of doping a semiconductor with trivalent atoms?
A.
Creates n-type
B.
Creates p-type
C.
No effect
D.
Increases resistance
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Solution
Doping a semiconductor with trivalent atoms creates p-type semiconductors by introducing holes.
Correct Answer: B — Creates p-type
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Q. What is the effect of doping a semiconductor?
A.
Increases resistance
B.
Decreases resistance
C.
No effect
D.
Makes it an insulator
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Solution
Doping a semiconductor decreases its resistance by introducing additional charge carriers.
Correct Answer: B — Decreases resistance
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Q. What is the effect of doping on the conductivity of a semiconductor?
A.
Decreases conductivity
B.
Increases conductivity
C.
No effect
D.
Makes it an insulator
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Solution
Doping a semiconductor increases its conductivity by introducing additional charge carriers.
Correct Answer: B — Increases conductivity
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Q. What is the effect of doping on the conductivity of semiconductors?
A.
Decreases conductivity
B.
Increases conductivity
C.
No effect
D.
Makes it insulative
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Solution
Doping increases the conductivity of semiconductors by introducing additional charge carriers.
Correct Answer: B — Increases conductivity
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Q. What is the effect of increasing the bandwidth of a communication channel?
A.
Increased data rate
B.
Decreased data rate
C.
No effect on data rate
D.
Increased noise
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Solution
Increasing the bandwidth allows for a higher data rate.
Correct Answer: A — Increased data rate
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Q. What is the effect of increasing the frequency of incident light on the photoelectric current?
A.
Increases indefinitely
B.
Decreases
C.
Remains constant
D.
Increases until a threshold frequency is reached
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Solution
The photoelectric current increases with frequency until the threshold frequency is reached, after which it depends on intensity.
Correct Answer: D — Increases until a threshold frequency is reached
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Q. What is the effect of increasing the intensity of light on the energy of emitted photoelectrons?
A.
Increases energy
B.
Decreases energy
C.
No effect on energy
D.
Energy becomes negative
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Solution
Increasing the intensity of light increases the number of emitted photoelectrons but does not affect their energy.
Correct Answer: C — No effect on energy
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Q. What is the effect of increasing the intensity of light on the energy of emitted electrons in the photoelectric effect?
A.
It increases the energy
B.
It decreases the energy
C.
It does not affect the energy
D.
It can either increase or decrease the energy
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Solution
Increasing the intensity of light increases the number of emitted electrons but does not affect their energy, which depends on the frequency.
Correct Answer: C — It does not affect the energy
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Q. What is the effect of increasing the intensity of light on the maximum kinetic energy of emitted electrons?
A.
It increases
B.
It decreases
C.
It remains the same
D.
It becomes zero
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Solution
The maximum kinetic energy of emitted electrons remains the same as it depends only on the frequency of the incident light, not its intensity.
Correct Answer: C — It remains the same
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Q. What is the effect of increasing the intensity of light on the maximum kinetic energy of the emitted electrons?
A.
It increases
B.
It decreases
C.
It remains the same
D.
It becomes zero
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Solution
The maximum kinetic energy of the emitted electrons is dependent only on the frequency of the incident light, not on its intensity.
Correct Answer: C — It remains the same
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Q. What is the effect of increasing the transmission power in a communication system?
A.
Increased range
B.
Decreased noise
C.
Higher bandwidth
D.
Lower distortion
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Solution
Increasing the transmission power generally increases the range of the communication system.
Correct Answer: A — Increased range
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Q. What is the effect of increasing the wavelength of incident light on the photoelectric current?
A.
It increases the current
B.
It decreases the current
C.
It has no effect
D.
It stops the current
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Solution
Increasing the wavelength decreases the frequency, which may fall below the threshold frequency, thus decreasing or stopping the current.
Correct Answer: B — It decreases the current
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Q. What is the effect of increasing the wavelength of incident light on the photoelectric effect?
A.
More electrons are emitted
B.
Fewer electrons are emitted
C.
The kinetic energy of emitted electrons increases
D.
The work function decreases
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Solution
Increasing the wavelength decreases the frequency of the incident light, which can lead to fewer or no electrons being emitted if the frequency falls below the threshold frequency.
Correct Answer: B — Fewer electrons are emitted
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Q. What is the effect of increasing the work function of a metal on the photoelectric effect?
A.
More electrons are emitted
B.
Fewer electrons are emitted
C.
The frequency of light must be increased
D.
Both B and C are correct
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Solution
Increasing the work function means that a higher frequency of light is required to emit electrons, resulting in fewer electrons being emitted for a given frequency of light.
Correct Answer: D — Both B and C are correct
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Q. What is the electron configuration of the element with atomic number 26?
A.
1s2 2s2 2p6 3s2 3p6 4s2 3d6
B.
1s2 2s2 2p6 3s2 3p6 4s2 3d5
C.
1s2 2s2 2p6 3s2 3p6 4s2 3d7
D.
1s2 2s2 2p6 3s2 3p6 4s2 3d8
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Solution
The electron configuration of iron (Fe), which has an atomic number of 26, is 1s2 2s2 2p6 3s2 3p6 4s2 3d6.
Correct Answer: A — 1s2 2s2 2p6 3s2 3p6 4s2 3d6
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Q. What is the energy band gap of silicon at room temperature?
A.
0.1 eV
B.
1.1 eV
C.
1.5 eV
D.
2.0 eV
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Solution
The energy band gap of silicon at room temperature is approximately 1.1 eV.
Correct Answer: B — 1.1 eV
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Q. What is the energy difference between the n=1 and n=2 levels in a hydrogen atom?
A.
10.2 eV
B.
13.6 eV
C.
1.89 eV
D.
3.4 eV
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Solution
The energy difference between n=1 and n=2 in hydrogen is 10.2 eV.
Correct Answer: A — 10.2 eV
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