An incandescent filament lamp and a fluorescent lamp are placed side by side. Each lamp is viewed through a high-resolution spectroscope that can display spectra from the near-ultraviolet through the visible range.
Use the observations below, together with relevant atomic principles, to answer the following questions.
• The incandescent lamp produces a continuous spectrum that gradually decreases in intensity toward the ultraviolet.
• The fluorescent lamp produces a series of narrow bright lines superimposed on a faint continuum whose overall shape differs from that of the incandescent lamp.
(a) Identify the type of spectrum (continuous, emission line, or absorption line) primarily produced by each lamp and describe the visual differences you would expect to see.
(b) Explain, in terms of atomic and molecular energy levels, why a heated tungsten filament emits a continuous spectrum whereas the low-pressure gas inside the fluorescent lamp emits predominantly line spectra.
(c) Some fluorescent lamps include a thin phosphor coating on the inside of the glass that absorbs ultraviolet photons and re-emits visible photons. Explain how this process influences the overall appearance of the fluorescent lamp’s spectrum.
(d) Predict how replacing the tungsten filament lamp with a very hot electric arc (temperature ≈ 10 000 K) would alter the shape of the continuous spectrum, and justify your prediction using appropriate physical reasoning.