physics : class12 Maximum Kinetic Energy : Particle Nature of Light : Dual Nature of Matter and Radiation MCQ Questions and Answers
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Maximum Kinetic Energy
MCQ questions and answers.
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MCQ Questions
1. Which equation gives the maximum kinetic energy of photoelectrons according to Einstein's photoelectric equation?
A.
K_max = hν + φ
B.
K_max = hν − φ
C.
K_max = φ − hν
D.
K_max = hφ − ν
Correct Answer:
K_max = hν − φ
Explanation:
The maximum kinetic energy is the energy of the incident photon minus the work function of the metal: K_max = hν − φ.
2. Light of photon energy 5 eV falls on a metal with work function 2 eV. What is the maximum kinetic energy of the emitted photoelectrons?
A.
2 eV
B.
3 eV
C.
5 eV
D.
7 eV
Correct Answer:
3 eV
Explanation:
Using K_max = photon energy − work function, K_max = 5 eV − 2 eV = 3 eV.
3. If the maximum kinetic energy of photoelectrons is 4 eV, what is the stopping potential?
A.
1 V
B.
2 V
C.
4 V
D.
8 V
Correct Answer:
4 V
Explanation:
The maximum kinetic energy in electron-volts is numerically equal to the stopping potential in volts. Therefore, 4 eV corresponds to 4 V.
4. For a given metal, what happens to the maximum kinetic energy of photoelectrons when the frequency of incident light is increased above the threshold frequency?
A.
It increases
B.
It decreases
C.
It becomes zero
D.
It remains exactly unchanged
Correct Answer:
It increases
Explanation:
Since K_max = hν − φ, increasing the frequency ν increases the maximum kinetic energy.
5. For light of fixed frequency falling on a given metal, which change does not affect the maximum kinetic energy of photoelectrons?
A.
Increasing the intensity of light
B.
Increasing the frequency of light
C.
Changing the work function of the metal
D.
Changing the wavelength of light
Correct Answer:
Increasing the intensity of light
Explanation:
For fixed frequency and metal, maximum kinetic energy depends on photon energy and work function, not on light intensity.
6. What is the maximum kinetic energy of photoelectrons when the frequency of incident light is exactly equal to the threshold frequency?
A.
Equal to the work function
B.
Equal to the photon energy
C.
Zero
D.
Maximum possible value
Correct Answer:
Zero
Explanation:
At threshold frequency, the photon energy is just sufficient to remove the electron, so no energy remains as kinetic energy.
7. A metal has a work function of 2.5 eV. If incident photons have energy 6.5 eV, what is the maximum kinetic energy of the photoelectrons?
A.
2.5 eV
B.
4.0 eV
C.
6.5 eV
D.
9.0 eV
Correct Answer:
4.0 eV
Explanation:
The maximum kinetic energy is K_max = 6.5 eV − 2.5 eV = 4.0 eV.
8. Two metals are illuminated with light of the same frequency. Metal X has a smaller work function than metal Y. Which metal emits photoelectrons with greater maximum kinetic energy?
A.
Metal X
B.
Metal Y
C.
Both have the same maximum kinetic energy
D.
Neither metal can emit photoelectrons
Correct Answer:
Metal X
Explanation:
For the same frequency, K_max = hν − φ. The smaller work function of metal X gives it greater maximum kinetic energy.
9. If the stopping potential for photoelectrons is increased from 2 V to 5 V, how does the maximum kinetic energy change?
A.
It decreases by 3 eV
B.
It increases by 3 eV
C.
It increases by 7 eV
D.
It remains zero
Correct Answer:
It increases by 3 eV
Explanation:
Maximum kinetic energy equals eV_s. Increasing the stopping potential by 3 V increases the maximum kinetic energy by 3 eV.
10. The maximum kinetic energy of photoelectrons is plotted against the frequency of incident light for a given metal. What is the slope of the graph?
A.
The work function
B.
The threshold frequency
C.
Planck's constant
D.
The stopping potential
Correct Answer:
Planck's constant
Explanation:
From K_max = hν − φ, a graph of maximum kinetic energy versus frequency has slope h, Planck's constant.
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