A laboratory has two identical photoelectric apparatuses
PHYSICS · Multi-part · CBSE · Physics · Dual Nature of Radiation and Matter · Dual Nature of Radiation and Matter
Problem
A laboratory has two identical photoelectric apparatuses, each equipped with an identical clean sodium surface. Apparatus 1 is illuminated with monochromatic light beam A; apparatus 2 is illuminated with monochromatic light beam B.
• Beam A has a frequency that is 1.20 times the threshold frequency for sodium and an intensity of 5.0 mW cm⁻².
• Beam B has a frequency that is 0.95 times the threshold frequency for sodium and an intensity of 50 mW cm⁻² (ten times as great as beam A).
Assume each beam uniformly illuminates an area of 1.0 cm² on its respective sodium surface.
(a) Describe qualitatively what, if anything, happens on each surface when illumination begins. In your answer, address whether electrons are emitted and how the emission (if any) differs between the two apparatuses.
(b) Suppose a variable stopping potential is applied in each apparatus. For the apparatus in which electrons are emitted, sketch on labeled axes (current versus stopping potential) the expected curve and indicate the stopping potential magnitude. No numerical values are required, but relative positions and shapes must be clear.
(c) The intensity of beam B is increased to 500 mW cm⁻² while its frequency remains unchanged. Explain whether this change alters (i) the existence of electron emission, (ii) the maximum electron kinetic energy, and (iii) the measurable photocurrent, providing a separate justification for each.
(d) A student claims that beam B should eventually eject electrons if its intensity is made sufficiently large. Construct a reasoned argument that evaluates this claim in light of the photon model of light.