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Concepts Of Physics MCQ Edition [Volume 2]PhysicsPhotoelectric Effect and Wave–Particle Duality

In a photoelectric effect experiment, the stopping potential is measured for monochromatic light beams of varying wavelengths. The collected data is as follows: wavelength (nm) 350 400 450 500 550 stopping potential (V) 1.45 1.00 0.66 0.38 0.16 Determine the Planck constant from this data.

Options

  1. A6.6 10⁻³⁴ eV s
  2. B2.1 10⁻¹⁵ eV s
  3. C4.2 10⁻¹⁵ eV s
  4. D4.2 10⁻¹⁵ J s

Correct answer

C. 4.2 10⁻¹⁵ eV s

Step-by-step solution

Einstein's photoelectric equation is given by: eV_s = hc - V_s = hc e ( 1 ) - e The slope of the V_s versus 1 graph is m = hc e . Taking the data points ₁ = 350 nm , V_ s1 = 1.45 V and ₂ = 400 nm , V_ s2 = 1.00 V : m = V_s ( 1 ) = 1.45 - 1.00 1 350 - 1 400 V nm m = 0.45 50 140000 = 0.45 2800 = 1260 V nm Equating this to hc e : hc e = 1260 10⁻⁹ V m h = 1260 10⁻⁹ eV m c = 1260 10⁻⁹ 3 10^8 eV s h = 420 10⁻¹⁷ eV s = 4.2 10⁻¹⁵ eV s

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