Question

The photoelectric effect can be used to measure the value of Planck’s constant. Suppose that a photoelectric effect experiment was carried out using light with ν = 7.50×10¹⁷ s^-1 and ejected electrons were detected with a kinetic energy of 2.50×10^-11 J. The experiment was then repeated using light with ν = 1.00×10¹⁸ s^-1 and the same metal target, and electrons were ejected with a kinetic energy of 5.00×10^-11 J. Use these data to find a value for Planck’s constant.

HINTS: these data are fictional and will give a result that is quite different from the real value of Planck’s constant. Be sure that you do not use the real value of Planck’s constant in any calculations here. It may help to start by thinking about how you would calculate the metal’s binding energy if you already knew Planck’s constant.

.........J s

Answer 1

Answer.

According to Einstein the Photoelectric effect should obey the equation,

where KE = Kinetic energy of emitted electron

v = frequency of incident light

v₀ = frequency for work function

Given that,

KE₁ = 2.50×10^-11 J ; v₁ = 7.50×10¹⁷ s^-1

KE₂ = 5×10^-11 J ; v₂ = 1.00×10¹⁸ s^-1

putting values in equation, we get

2.50×10^-11 = h*(7.50×10¹⁷ -v₀) - (equation 1)

5×10^-11 = h*(1.00×10¹⁸ -v₀) - (equation 2)

hence, equation (2-1) gives us

2.5*10^-11 = h*(2.5*10¹⁷)

h = 10^-28 J-s

Therefore,

Planck's constant = 10^-28 J-s.