Question

In an experiment on photoelectric effect, the stopping potential is measured for monochromatic light beams corresponding to different wavelengths. The data collected are as follows
Wavelength (nm) 350 400 450 500 550
Stopping potential (V) 1.45 1.00 0.66 0.38 0.16
Plot the stopping potential against inverse of wavelength (1/λ) on a graph paper and find (a) Planck's constant (b) the work function of the emitter and (c) the threshold wavelength.

Answer 1

(a) Planck's constant is $4.2 \times 10^{-15} \mathrm{eV}-\mathrm{s}$

(b) work function is 2.15 ev

(c)  the threshold wavelength is 576.8 nm

Explanation:

Step 1:

given data in the question  

λ = 350, $V_{s}$ = 1.45

λ = 400, $V_{s}$ = 1  

Step 2:

$\begin{array}{l}{\therefore \frac{h c}{350}=w+1.45 \quad \cdots \text { eq}^{n}(1)} \\{\frac{h c}{400}=w+1 \quad \ldots \text { eq }^{n}(2)}\end{array}$

We get: Subtract ( 2 ) from ( 1 ) and solve to get the value of h

(a) Planck's constant

$h=4.2 \times 10^{-15} \mathrm{eV}-\mathrm{s}$

(b) work function is,

$w=\frac{12240}{350}-1.45=2.15 e v$

(c)  the threshold wavelength,

$\begin{aligned}&w=\frac{n c}{\lambda}\\&\lambda_{\text {threshold}}=h c w\\&\lambda_{\text {threshold }}=\frac{1240}{1.15}\\&\lambda_{\text {threshold}}=576.8 \mathrm{nm}\end{aligned}$