# Wavelenght of the incident light

#### wyclefchick

1. Homework Statement
An incident light shines on a mercury metal plate with a work function of -4.5 eV. The stopping voltage is observed to be -1.65 volts. What is the wavelenght of the incident light?

2. Homework Equations
wavelength=hc/E-0(it's a Greek sign n i dont have it in my computer)

3. The Attempt at a Solution
(4.14 X 10^-15 eVs) (3 X 10^8 m/s) / 1.65 + 4.5 = 1.242 X 10^-6 / 6.15

1.242(10^2)/6.15 = 20.1954

but the right answer is 201.7561 nm

so can anyone please tell me what did I do wrong?

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#### rock.freak667

Homework Helper
$$\frac{hc}{\lambda}=\phi +eV_s$$

Did you use the correct value for h in eV?

#### wyclefchick

i used h=4.14 X 10^ -15 am i supposed to use the other one? h=6.626 X 10^-34 ?

#### rock.freak667

Homework Helper
How'd you go from 1.242 X 10^-6 / 6.15 to 1.242(10^2)/6.15 = 20.1954?

Because if you work out 1.242 X 10^-6 / 6.15 you'd get your answer.

#### wyclefchick

I was following one of the examples that my teacher did in class.

well if i do 1.242 X 10^-6 / 6.15...it equals 2.01951 but the right answer is 201.7561 nm

#### rock.freak667

Homework Helper
1.242 X 10^-6 / 6.15 =201nm

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