Einstein's photoelectric equation and the particle nature of light — practice questions

Question 1 · difficulty L1 · recall

Einstein's photoelectric equation is

• A. hf = φ + Kmax
• B. hf=φ-Kmax
• C. h/f=φ+Kmax
• D. hf=Kmax only for every metal

Question 2 · difficulty L1 · understanding

The work function φ of a metal is

• A. the energy of every emitted electron
• B. the minimum energy needed to remove an electron from its surface
• C. the stopping potential in volts regardless of charge
• D. the photon momentum

Question 3 · difficulty L2 · understanding

The ratio of the power of a light source $S_1$ to that the light source $S_2$ is $2 . S_1$ is emitting $2 \times 10^{15}$ photons per second at 600 nm . If the wavelength of the source $S_2$ is 300 nm , then the number of photons per second emitted by $S_2$ is __________ $\times 10^{14}$.

Question 4 · difficulty L2 · understanding

A monochromatic source of light operating at 15 kW emits $2.5 \times 10^{22}$ photons $/ \mathrm{s}$. The region of an electromagnetic spectrum to which the emitted electromagnetic radiation belongs to $\_\_\_\_$。 (Take $h=6.6 \times 10^{-34} \mathrm{~J} . \mathrm{s}$ and $c=3 \times 10^8 \mathrm{~m} / \mathrm{s}$ ).

• A. Microwave
• B. Infrared
• C. Visible
• D. Ultraviolet

Question 5 · difficulty L2 · understanding

Number of photons of equal energy emitted per second by a 6 mW laser source operating at 663 nm is ________. (Given : $h = 6.63 \times 10^{-34}$ J.s and $c=3\times10^{8}$ m/s)

• A. $10 \times 10^{15}$
• B. $5 \times 10^{16}$
• C. $5 \times 10^{15}$
• D. $2 \times 10^{16}$

Question 6 · difficulty L2 · understanding

The radiation pressure exerted by a 450 W light source on a perfectly reflecting surface placed at 2 m away from it, is

• A. $3 \times 10^{-8}$ Pascals
• B. 0
• C. $1.5 \times 10^{-8}$ Pascals
• D. $6 \times 10^{-8}$ Pascals

Question 7 · difficulty L2 · understanding

Which of the following phenomena cannot be explained by wave theory of light?

• A. Refraction of light
• B. Reflection of light
• C. Diffraction of light
• D. Compton effect

Question 8 · difficulty L2 · understanding

Which of the following phenomena does not explain by wave nature of light. A. reflection B. diffraction C. photoelectric effect D. interference E. polarization Choose the most appropriate answer from the options given below:

• A. C only
• B. B, D only
• C. A, C only
• D. E only

Question 9 · difficulty L2 · understanding

Monochromatic light of frequency $6 \times 10^{14} \mathrm{~Hz}$ is produced by a laser. The power emitted is $2 \times 10^{-3} \mathrm{~W}$. How many photons per second on an average, are emitted by the source ? (Given $\mathrm{h}=6.63 \times 10^{-34} \mathrm{Js}$ )

• A. $5 \times 10^{15}$
• B. $7 \times 10^{16}$
• C. $6 \times 10^{15}$
• D. $9 \times 10^{18}$

Question 10 · difficulty L2 · understanding

Conductivity of a photodiode starts changing only if the wavelength of incident light is less than $660 \mathrm{~nm}$. The band gap of photodiode is found to be $\left(\frac{\mathrm{X}}{8}\right) \mathrm{eV}$. The value of $\mathrm{X}$ is : (Given, $\mathrm{h}=6.6 \times 10^{-34} \mathrm{Js}, \mathrm{e}=1.6 \times 10^{-19} \mathrm{C}$ )

• A. 11
• B. 13
• C. 15
• D. 21