l(nm) Vstop (volts) 500 .19 450 .48 400 .83 350 1.28 300 1.89 250 2.74 In a phot

Question

    

l(nm)

Vstop (volts)

500

.19

450

.48

400

.83

350

1.28

300

1.89

250

2.74

    
    In a photoelectric effect experiment, the stopping potential was measured for several different wavelengths of incident light. The data are shown in the table. Analyze these data to determine (a) the metal used for the cathode and (b) an experimental value for Planck

                

l(nm)

                                 

Vstop (volts)

                                 

500

                                 

.19

                                 

450

                                 

.48

                                 

400

                                 

.83

                                 

350

                                 

1.28

                                 

300

                                 

1.89

                                 

250

                                 

2.74

                

Explanation / Answer

let the work function be a and the planc's constant be h.so,

V*e+a=hc/lambda

so,

0.18*1.6*10^-19+a*1.6*10^-19=h*3*10^8/(500*10^-9)

also,

0.48*1.6*10^-19+a*1.6*10^-19=h*3*10^8/(450*10^-9)

so, a=2.52 eV

and h=7.2*10^-34

so,

a)the metal is strontium (closest)

b)h=7.2*10^-34 Js

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