A cavity radiator is used in a laboratory to study thermal emission at two temperatures
PHYSICS · Multi-part · CBSE · Physics · Thermal Properties of Matter · Thermal Properties of Matter
Problem
A cavity radiator is used in a laboratory to study thermal emission at two temperatures.
• At T1=1500K the measured spectral–intensity distribution peaks at a wavelength of λpeak,1=1.9μm.
• When the cavity is heated to T2=3000K the peak shifts to λpeak,2=0.95μm, and the measured intensity at λ=0.20μm is finite and comparable to the intensity at λ=1.5μm.
Earlier classical predictions suggested that, as wavelength became very small, the spectral intensity should increase without limit.
(a) State the key classical assumption about the distribution of electromagnetic modes inside a cavity and describe the qualitative dependence of spectral intensity on wavelength that it predicts for short wavelengths.
(b) Explain, with reference to energy distribution among modes, how this classical prediction leads to the so-called “ultraviolet catastrophe.”
(c) Using the experimental observations provided, discuss how introducing quantized energy exchanges for the electromagnetic modes resolves the conflict between theory and experiment.
(d) Based on the shift in λpeak with temperature and the finite measured intensity at 0.20μm, justify whether the phenomenon of blackbody radiation is best described by considering light as waves, particles, or by invoking both descriptions. Support your answer with two specific arguments drawn from the data.