Dual Nature of Matter

JEE Main level, single correct, medium

90 of 200

Question 90 of 200

K1K_1 and K2K_2 be the maximum kinetic energies of photoelectrons emitted from a surface of a given material for the light of wavelength λ1\lambda_1 and λ2\lambda_2, respectively. If λ1=2λ2\lambda_1=2\lambda_2 then the work function of material is given by:

Show answer and solution

Answer: (D) K2−2K1K_2-2K_1

Using Einstein's photoelectric equation:

K1=hcλ1−ϕK_1 = \dfrac{hc}{\lambda_1} - \phi

K2=hcλ2−ϕK_2 = \dfrac{hc}{\lambda_2} - \phi

Given λ1=2λ2\lambda_1 = 2\lambda_2, the first equation becomes:

K1=hc2λ2−ϕK_1 = \dfrac{hc}{2\lambda_2} - \phi

Multiplying by 22:

2K1=hcλ2−2ϕ2K_1 = \dfrac{hc}{\lambda_2} - 2\phi

Substituting hcλ2=K2+ϕ\dfrac{hc}{\lambda_2} = K_2 + \phi from the second equation:

2K1=(K2+ϕ)−2ϕ2K_1 = (K_2 + \phi) - 2\phi

2K1=K2−ϕ2K_1 = K_2 - \phi

ϕ=K2−2K1\phi = K_2 - 2K_1

Answer: K2−2K1K_2-2K_1

JEE Main question paper PDF

Open a shift to read the full paper on this page, or download it.

JEE Main 2025 Apr 2 Shift 1 question paper

Open Download PDF

Opening paper…

Explain it as a whiteboard videoStep-by-step, in Hinglish or English. Your first video needs no login.Solved it on paper but got it wrong?Upload a photo of your working. Mistake Doctor marks the exact line that broke.
See it move: Photoelectric effect and matter waves simulationDrag the sliders and watch the numbers in this question change.Revise Modern Physics firstFormula sheet, solved examples and the traps students fall into.

More Physics practice

JEE Main Physics practice question on Dual Nature of Matter (Photoelectric Effect), with the answer and a step-by-step solution. Scan a question from your own book or paper to get a whiteboard video.