Question

When radiation of wavelength `lambda ` is incident on a metallic surface , the stopping potential is `4.8 "volts"` . If the same surface is illuminated with radiation of double the wavelength , then the stopping potential becomes `1.6 "volts"`. Then the threshold wavelength for the surface is
A. `2 lambda`
B. `4 lambda`
C. `6 lambda`
D. `8 lambda`

Answer 1

Correct Answer - B
By using `(hc )/( e ) ((1)/(lambda) - (1)/(lambda_(0))) = V_(0)`
`rArr (hc )/( e) ((1)/(lambda) - (1)/(lambda_(0))) = 4.8` …..(i)
and (`hc )/( e) ((1)/( 2 lambda) - (1)/(lambda_(0))) = 1.6` …… (ii)
`"From equation"` (i) and (ii) ,
`(((1)/(lambda) - (1)/(lambda_(0))))/(((1)/( 2 lambda) - (1)/(lambda_(0)))) = (4.8)/(1.6) rArr lambda_(0) = 4 lambda`.