What is the threshold wavelength for a metal whose work function is 2.0 eV (h = 6.63 × 10⁻³⁴ J s, c = 3.0 × 10⁸ m/s, e = 1.6 × 10⁻¹⁹ C)?
Correct answer C. 622 nm
Topic / 30 questions
Dawn of Modern Physics MCQs
Dawn of Modern Physics MCQs cover the particle model of light, photon energy, the photoelectric effect with work function and stopping potential, and Compton scattering. They help MDCAT, ECAT and FSc candidates revise the ideas of quantum physics and short photon calculations, and every question on MCQs360 shows its correct answer instantly.
- Electromagnetic Induction 30
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- Work and Energy 30
- Waves 30
- Vectors and Equilibrium 30
- Nuclear Physics 30
- Dawn of Modern Physics 30
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- Rotational and Circular Motion 30
- Atomic Spectra 30
- Alternating Current 30
- Force and Motion 30
An X-ray photon has a wavelength of 0.10 nm. What is its energy in keV (h = 6.63 × 10⁻³⁴ J s, c = 3.0 × 10⁸ m/s, e = 1.6 × 10⁻¹⁹ C)?
Correct answer C. 12.4 keV
A photon has an energy of 6.63 × 10⁻¹⁹ J. What is its frequency (h = 6.63 × 10⁻³⁴ J s)?
Correct answer B. 1.0 × 10¹⁵ Hz
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What is the ratio of the energy of a 400 nm photon to that of a 600 nm photon?
Correct answer A. 1.5
Photons of energy 5.0 eV strike a metal of work function 3.2 eV. What is the stopping potential?
Correct answer A. 1.8 V
A metal has a work function of 2.3 eV. What is its threshold frequency (h = 6.63 × 10⁻³⁴ J s, e = 1.6 × 10⁻¹⁹ C)?
Correct answer D. 5.6 × 10¹⁴ Hz
Photons of energy 3.5 eV fall on a metal of work function 2.0 eV. What is the maximum kinetic energy of the emitted electrons?
Correct answer B. 1.5 eV
A laser of power 1.0 mW emits light of wavelength 633 nm. About how many photons does it emit per second (h = 6.63 × 10⁻³⁴ J s, c = 3.0 × 10⁸ m/s)?
Correct answer B. 3.2 × 10¹⁵
What is the momentum of a photon of wavelength 663 nm (h = 6.63 × 10⁻³⁴ J s)?
Correct answer C. 1.0 × 10⁻²⁷ kg m/s
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A photon has an energy of 3.0 eV. What is its wavelength (h = 6.63 × 10⁻³⁴ J s, c = 3.0 × 10⁸ m/s, e = 1.6 × 10⁻¹⁹ C)?
Correct answer D. 414 nm
What is the value of one electron-volt in joules?
Correct answer C. 1.6 × 10⁻¹⁹ J
What is the energy, in electron-volts, of a photon of wavelength 500 nm (h = 6.63 × 10⁻³⁴ J s, c = 3.0 × 10⁸ m/s, e = 1.6 × 10⁻¹⁹ C)?
Correct answer B. 2.49 eV
What is the energy of a photon of frequency 5.0 × 10¹⁴ Hz (h = 6.63 × 10⁻³⁴ J s)?
Correct answer D. 3.3 × 10⁻¹⁹ J
In Compton scattering of X-rays by free electrons, how does the wavelength of the scattered photon compare with that of the incident photon?
Correct answer A. It is longer
Which phenomenon provides clear evidence for the particle nature of light?
Correct answer B. The photoelectric effect
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Which equation is Einstein’s photoelectric equation?
Correct answer A. hf = φ + K.E.max
For light above the threshold frequency, the photoelectric current is proportional to ____
Correct answer B. the intensity of the light
How does the speed of a photon in vacuum depend on its frequency?
Correct answer B. It is the same for all frequencies
Which expression gives the momentum of a photon of wavelength λ?
Correct answer D. p = h/λ
On what does the stopping potential in a photoelectric experiment depend?
Correct answer A. The frequency of the light and the work function of the metal
About Dawn of Modern Physics MCQs
Questions in this unit start with the photon as a packet of electromagnetic energy and ask you to calculate its energy, frequency or wavelength using Planck's constant, often converting between joules and electronvolts. Photoelectric questions use Einstein's equation to find the maximum kinetic energy of emitted electrons and ask what the stopping potential, threshold frequency and photoelectric current depend on, separating the effects of frequency and intensity. Compton scattering questions test how the wavelength of an X-ray photon changes after it scatters off a free electron.
Key facts to remember
- Photon energy: E = hf = hc/λ, where h = 6.63 × 10⁻³⁴ J s.
- Einstein's photoelectric equation: hf = φ + K.E.ₘₐₓ, where the work function φ = hf₀.
- Maximum kinetic energy of photoelectrons is K.E.ₘₐₓ = eV₀, where V₀ is the stopping potential.
- K.E.ₘₐₓ and stopping potential depend on frequency of light, not its intensity; photocurrent is proportional to intensity.
- No photoelectrons are emitted below the threshold frequency f₀, however intense the light.
- Compton shift: Δλ = (h/m₀c)(1 − cos θ), so the scattered photon has a longer wavelength.
Exams that include Dawn of Modern Physics MCQs
Pakistan
- MDCAT
- ECAT (UET)
- NUMS
- AKU
- FSc boards
India
- NEET
- JEE Main
Bangladesh
- HSC
- Medical Admission Test
How to prepare for Dawn of Modern Physics MCQs
- Use the shortcut λ (nm) ≈ 1240/E (eV) to check photon wavelength answers quickly.
- Keep eV and joules apart: divide joules by 1.6 × 10⁻¹⁹ to get electronvolts.
- For 'depends on' questions, remember frequency controls energy per electron and intensity controls the number of electrons.
- Revise this unit together with Atomic Spectra, since both rely on E = hf.
Frequently asked questions
Which exams ask Dawn of Modern Physics MCQs?
Dawn of Modern Physics is part of the FSc physics syllabus, so its MCQs appear in MDCAT, ECAT (UET), NUMS and AKU entry tests and in FSc board papers. Students in India meet the same ideas in NEET and JEE Main, and Bangladeshi students in HSC and the medical admission test.
What is the work function of a metal?
The work function is the minimum energy needed to remove an electron from the surface of a metal. It equals hf₀, where f₀ is the threshold frequency. Light of lower frequency cannot cause photoelectric emission, whatever its intensity, because each photon carries too little energy.
Last reviewed October 2026