Question

When two light beams of wavelengths 1and fall on a metal surface, they produce photoelectrons with energies 115 eV and 254 eV respectively. Estimate the numerical value of the Planck constant.

Answer 1

You had some formatting error when you posted your question.

What are the wavelengths of the two beams?

You're going to use the formula:

E = hf

E is energy
h is Planck's constant (which is what you're solving for)
f is frequency

You'll notice that we we're given the energy (115 eV and 254 eV) but we don't know the frequencies.

You use another formula to calculate the frequency

\( c = \lambda f\)

c is the speed of light which is a constant 3.0*10^8 m/s
\(\lambda\) is the wavelength which is given to you in your question
f is the frequency

You could plug that into the first formula to get

\(\sf E = \dfrac{h c}{\lambda}\)

You have values for everything besides 'h' which is what you're trying to solve for

Answer 2

Let me know how far you get in solving your problem or if you'd like any further clarification :)