Photons & Photon Energy — MH-CET Physics MCQs with Solutions
Free MH-CET Physics Photons & Photon Energy MCQs with step-by-step solutions (21 questions). Part of Dual Nature of Radiation and Matter. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Photons & Photon Energy · easy · theory
The energy of a photon of frequency $\nu$ is:
A. $\dfrac{h}{\nu}$
B. $\dfrac{\nu}{h}$
C. $h\nu$ ✓ Correct
D. $h\nu^2$
Solution: Equivalently $E = \dfrac{hc}{\lambda}$, so shorter wavelengths carry more energy per photon.
Q2 — Photons & Photon Energy · medium · theory
The momentum of a photon of wavelength $\lambda$ is:
A. $\dfrac{h}{\lambda}$ ✓ Correct
B. $\dfrac{\lambda}{h}$
C. $\dfrac{h}{c\lambda}$
D. $h\lambda$
Solution: It follows from $p = \dfrac{E}{c} = \dfrac{h\nu}{c} = \dfrac{h}{\lambda}$.
Q3 — Photons & Photon Energy · easy · theory
The rest mass of a photon is:
A. Infinite
B. Equal to the electron mass
C. Zero ✓ Correct
D. Dependent on its frequency
Solution: Only a massless particle can travel at exactly the speed of light, yet it still carries energy and momentum.
Q4 — Photons & Photon Energy · easy · theory
Photons travel in free space with a speed:
A. That increases with frequency
B. That depends on the intensity of the beam
C. Equal to $c$, independent of their frequency ✓ Correct
D. That decreases with frequency
Solution: All electromagnetic radiation propagates through vacuum at the same speed.
Q5 — Photons & Photon Energy · easy · theory
A photon is:
A. Negatively charged
B. Charged depending on its energy
C. Positively charged
D. Electrically neutral ✓ Correct
Solution: Being uncharged, a photon is undeflected by electric and magnetic fields.
Q6 — Photons & Photon Energy · medium · theory
For a beam of monochromatic light, the intensity determines:
A. The energy of each photon
B. The number of photons arriving per second ✓ Correct
C. The speed of the photons
D. The wavelength of the light
Solution: Brightness counts photons; colour fixes the energy each one carries.
Q7 — Photons & Photon Energy · medium · theory
The energy of an individual photon in a beam is:
A. Inversely proportional to the intensity
B. Proportional to the intensity
C. Independent of the intensity of the beam ✓ Correct
D. Proportional to the square of the intensity
Solution: This is precisely why a very bright red lamp cannot eject electrons that faint blue light can.
Q8 — Photons & Photon Energy · easy · theory
The value of Planck's constant is approximately:
A. $1.6 \times 10^{-19}\text{ J}\cdot\text{s}$
B. $3 \times 10^8\text{ J}\cdot\text{s}$
C. $6.63 \times 10^{-34}\text{ J}\cdot\text{s}$ ✓ Correct
D. $6.63 \times 10^{-19}\text{ J}\cdot\text{s}$
Solution: Its extreme smallness is why quantum effects are invisible in everyday life.
Q9 — Photons & Photon Energy · medium · numerical
The energy of a photon of wavelength $500\text{ nm}$ is approximately ($hc = 1240\text{ eV}\cdot\text{nm}$):
A. $3.1\text{ eV}$
B. $1.24\text{ eV}$
C. $2.48\text{ eV}$ ✓ Correct
D. $4.96\text{ eV}$
Solution: $E = \dfrac{1240}{500} = 2.48\text{ eV}$.
Q10 — Photons & Photon Energy · medium · numerical
The energy of a photon of wavelength $600\text{ nm}$ is approximately:
A. $2.48\text{ eV}$
B. $2.07\text{ eV}$ ✓ Correct
C. $3.1\text{ eV}$
D. $1.24\text{ eV}$
Solution: $E = \dfrac{1240}{600} \approx 2.07\text{ eV}$.
Q11 — Photons & Photon Energy · hard · numerical
The energy of a photon of wavelength $500\text{ nm}$ in joule is approximately:
A. $6.63 \times 10^{-34}\text{ J}$
B. $3.97 \times 10^{-19}\text{ J}$ ✓ Correct
C. $3.97 \times 10^{-18}\text{ J}$
D. $1.33 \times 10^{-27}\text{ J}$
Solution: $E = \dfrac{hc}{\lambda} = \dfrac{6.63 \times 10^{-34} \times 3 \times 10^8}{5 \times 10^{-7}} \approx 3.97 \times 10^{-19}\text{ J}$.
Q12 — Photons & Photon Energy · hard · numerical
The momentum of a photon of wavelength $500\text{ nm}$ is approximately:
A. $1.33 \times 10^{-27}\text{ kg}\cdot\text{m/s}$ ✓ Correct
B. $3.97 \times 10^{-19}\text{ kg}\cdot\text{m/s}$
C. $6.63 \times 10^{-34}\text{ kg}\cdot\text{m/s}$
D. $1.33 \times 10^{-24}\text{ kg}\cdot\text{m/s}$
Solution: $p = \dfrac{h}{\lambda} = \dfrac{6.63 \times 10^{-34}}{5 \times 10^{-7}} \approx 1.33 \times 10^{-27}\text{ kg}\cdot\text{m/s}$.
Q13 — Photons & Photon Energy · medium · numerical
The energy of a photon of frequency $6 \times 10^{14}\text{ Hz}$ is approximately:
A. $3.98 \times 10^{-19}\text{ J}$ ✓ Correct
B. $6.63 \times 10^{-19}\text{ J}$
C. $1.99 \times 10^{-19}\text{ J}$
D. $3.98 \times 10^{-20}\text{ J}$
Solution: $E = h\nu = 6.63 \times 10^{-34} \times 6 \times 10^{14} \approx 3.98 \times 10^{-19}\text{ J}$.
Q14 — Photons & Photon Energy · easy · numerical
If the energy of a photon is doubled, its wavelength:
A. Doubles
B. Becomes four times
C. Halves ✓ Correct
D. Remains unchanged
Solution: $E = \dfrac{hc}{\lambda} \propto \dfrac{1}{\lambda}$.
Q15 — Photons & Photon Energy · hard · numerical
A $100\text{ W}$ lamp emits light of wavelength $500\text{ nm}$. The number of photons emitted per second is approximately:
A. $2.5 \times 10^{18}$
B. $4 \times 10^{19}$
C. $2.5 \times 10^{20}$ ✓ Correct
D. $1.5 \times 10^{22}$
Solution: Each photon carries $3.97 \times 10^{-19}\text{ J}$, so $N = \dfrac{100}{3.97 \times 10^{-19}} \approx 2.5 \times 10^{20}$ per second.
Q16 — Photons & Photon Energy · medium · numerical
The energy of a photon of wavelength $200\text{ nm}$ is approximately:
A. $2.48\text{ eV}$
B. $3.1\text{ eV}$
C. $12.4\text{ eV}$
D. $6.2\text{ eV}$ ✓ Correct
Solution: $E = \dfrac{1240}{200} = 6.2\text{ eV}$.
Q17 — Photons & Photon Energy · hard · numerical
A photon has energy $3.97 \times 10^{-19}\text{ J}$. Its momentum is approximately:
A. $1.19 \times 10^{-10}\text{ kg}\cdot\text{m/s}$
B. $1.32 \times 10^{-24}\text{ kg}\cdot\text{m/s}$
C. $3.97 \times 10^{-27}\text{ kg}\cdot\text{m/s}$
D. $1.32 \times 10^{-27}\text{ kg}\cdot\text{m/s}$ ✓ Correct
Solution: $p = \dfrac{E}{c} = \dfrac{3.97 \times 10^{-19}}{3 \times 10^8} \approx 1.32 \times 10^{-27}\text{ kg}\cdot\text{m/s}$.
Q18 — Photons & Photon Energy · easy · numerical
A photon of wavelength $1240\text{ nm}$ has energy:
A. $2\text{ eV}$
B. $1240\text{ eV}$
C. $0.5\text{ eV}$
D. $1\text{ eV}$ ✓ Correct
Solution: $E = \dfrac{1240}{1240} = 1\text{ eV}$.
Q19 — Photons & Photon Energy · hard · numerical
The momentum of a photon of wavelength $0.5\text{ nm}$ is approximately:
A. $6.63 \times 10^{-34}\text{ kg}\cdot\text{m/s}$
B. $3.3 \times 10^{-25}\text{ kg}\cdot\text{m/s}$
C. $1.33 \times 10^{-24}\text{ kg}\cdot\text{m/s}$ ✓ Correct
D. $1.33 \times 10^{-27}\text{ kg}\cdot\text{m/s}$
Solution: $p = \dfrac{6.63 \times 10^{-34}}{5 \times 10^{-10}} \approx 1.33 \times 10^{-24}\text{ kg}\cdot\text{m/s}$.
Q20 — Photons & Photon Energy · hard · numerical
An X-ray photon of wavelength $1\text{ \AA}$ has energy approximately:
A. $1.24\text{ keV}$
B. $124\text{ eV}$
C. $12.4\text{ eV}$
D. $12.4\text{ keV}$ ✓ Correct
Solution: $1\text{ \AA} = 0.1\text{ nm}$, so $E = \dfrac{1240}{0.1} = 12400\text{ eV} = 12.4\text{ keV}$.
Q21 — Photons & Photon Energy · easy · numerical
Two photons have wavelengths $400\text{ nm}$ and $800\text{ nm}$. The ratio of their energies is:
A. $4 : 1$
B. $1 : 2$
C. $2 : 1$ ✓ Correct
D. $1 : 4$
Solution: $E \propto \dfrac{1}{\lambda}$, so the shorter wavelength carries twice the energy.