Opaque Sodium Flame
Safety Warnings
Warning: Open Flame Hazard
Warning: Hot Equipment
Purpose
Demonstrates that sodium vapor absorbs the same wavelengths it emits (the D-doublet at 589.0 and 589.6 nm). A salt-laden candle flame becomes opaque to sodium lamp light while remaining transparent to mercury lamp light, visually illustrating resonance absorption and quantized energy levels.
Figure 1:
The oil lamp flame casts two shadows on the wall: an orange-yellow shadow from the sodium lamp (left) and a blue-gray shadow from the mercury lamp (right). Introducing salt on the spatula into the flame adds a dark flame shape to only the sodium shadow.
Figure 2:
Full setup: oil lamp on scissor jack (left) for height adjustment, sodium lamp (center), and watch glass with salt on a stand (right). The lamps face the blackboard to cast shadows.
Equipment
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