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According to Einstein:

w_o = work function - work to pull away electron

(different for each metal)

hf = Energy of light used

E_max = Energy of photoelectron (Max KE given to electron)

Electronvolt - very small energy unit: 1 eV = 1.6 X 10^-19 J

Einstein uses
y = mx + b to get his equation!

2. Threshold frequency - minimum frequency needed to expel electrons 

Explained by Einstein

Typical plot of Frequency vs. E_max (Maximum KE of photoelectron)
 

Frequency

What's the threshold frequency of:

Metal A?

    f_o = 1.0 X 10¹⁴ Hz

Metal B?

Frequency

f_o = 2.5 X 10¹⁴ Hz

Frequency

Metal C?

    f_o = 3.75 X 10¹⁴ Hz

Which metal has the greatest work function?

Frequency

Work Function - energy needed to pull away electron from atom.

***W_o = hf_o

_{h = Planck's Constant
p.1 Reference}

Ex 1) If a metal would only emit electrons when exposed to high frequency light what does that tell you about its work function?

Work function must be high

Ex) If the work function (W_o) of particular metal = 5.0 x 10^-19 J Find the threshold frequency (f_o) ( h = 6.63 x 10^-34 Js )

W_o = hf_o

f_o = w/h

= (5 x 10^-19 J/(6.63 x 10^-34 Js)

f_o = 7.5 x 10¹⁴ Hz 

Since KE_max= hf - w_o

Then …

KE _max= hf - hf_o

(Use equation if given only frequencies)

PHOTON BY PHOTON DEVELOPMENT OF A PHOTOGRAPH -