Photoelectric effect; Hertz and Lenard observations — practice questions

Question 1 · difficulty L1 · recall

Photoelectric emission occurs when light causes electrons to be emitted from

• A. only a vacuum with no material
• B. a resistor without illumination
• C. a material surface, commonly a metal
• D. a magnetic field alone

Question 2 · difficulty L1 · understanding

Threshold frequency is the

• A. maximum emitted-electron frequency
• B. frequency at which current is always zero regardless of voltage
• C. same universal value for all metals
• D. minimum frequency needed to produce photoemission from a given surface

Question 3 · difficulty L2 · understanding

An atom absorbs a photon of wavelength $$500 \mathrm{~nm}$$ and emits another photon of wavelength $$600 \mathrm{~nm}$$. The net energy absorbed by the atom in this process is $$n \times 10^{-4} ~\mathrm{eV}$$. The value of n is __________. [Assume the atom to be stationary during the absorption and emission process] (Take $$\mathrm{h}=6.6 \times 10^{-34} ~\mathrm{Js}$$ and $$\mathrm{c}=3 \times 10^{8} \mathrm{~m} / \mathrm{s}$$ )

Question 4 · difficulty L2 · understanding

When light of frequency twice the threshold frequency is incident on the metal plate, the maximum velocity of emitted electron is v 1 . When the frequency of incident radiation is increased to five times the threshold value, the maximum velocity of emitted electron becomes v 2 . If v 2 = x v 1 , the value of x will be __________.

Question 5 · difficulty L2 · understanding

The work functions of silver and sodium are 4.6 and 2.3 eV, respectively. The ratio of the slope of the stopping potential versus frequency plot for silver to that of sodium is ___________.

Question 6 · difficulty L2 · understanding

$K_1$ and $K_2$ be the maximum kinetic energies of photoelectrons emitted from a surface of a given material for the light of wavelength $\lambda_1$ and $\lambda_2$, respectively. If $\lambda_1=2 \lambda_2$ then the work function of material is given by :

• A. $$K_2+2 K_1$$
• B. $$2 K_2-K_1$$
• C. $$K_1-2 K_2$$
• D. $$K_2-2 K_1$$

Question 7 · difficulty L2 · understanding

Light source having wavelength 331 nm is used to generate photo-electrons whose stopping potential is 0.2 V . The work function of the used metal in the experiment is $\alpha \times 10^{-19} \mathrm{~J}$. The value of $\alpha$ is $\_\_\_\_$ . $$\left(\mathrm{h}=6.62 \times 10^{-34} \mathrm{~J} \mathrm{~s}, \mathrm{e}=1.6 \times 10^{-19} \mathrm{C} \text { and } \mathrm{c}=3 \times 10^8 \mathrm{~m} / \mathrm{s}\right)$$

• A. 3.68
• B. 4.68
• C. 5.68
• D. 2.68

Question 8 · difficulty L2 · understanding

The graph shows variation of stopping potential $V_{\mathrm{o}}$ with the frequency $v$ of the incident radiation for three photosensitive metals $X_1, X_2$ and $X_3$. Which metal will give out electrons with greater kinetic energy, for the same wavelength of incident radiation?

• A. $X_1$
• B. $X_2$
• C. $X_3$
• D. All the metals will give out photo electrons with same kinetic energies.

Question 9 · difficulty L2 · understanding

For a certain metal, when monochromatic light of wavelength $\lambda$ is incident, the stopping potential for photoelectrons is $3V_0$. When the same metal is illuminated by light of wavelength $2\lambda$, then the stopping potential becomes $V_0$. The threshold wavelength for photoelectric emission for the given metal is $\alpha \lambda$. The value of $\alpha$ is ______.

• A. 1
• B. 4
• C. 2
• D. 3

Question 10 · difficulty L2 · understanding

Light is incident on a metallic plate having work function $110 \times 10^{-20} \mathrm{~J}$. If the produced photoelectrons have zero kinetic energy then the angular frequency of the incident light is $\_\_\_\_$ rad/s. $\left(\mathrm{h}=6.63 \times 10^{-34} \mathrm{~J} . \mathrm{s}\right)$.

• A. $1.04 \times 10^{13}$
• B. $1.66 \times 10^{16}$
• C. $1.66 \times 10^{15}$
• D. $1.04 \times 10^{16}$