Action of a Lens
Safety Warnings
Warning: Hot Lamp Warning
Warning: Electrical Safety
Warning: Eye Protection Advisory
Purpose
Demonstrates the focusing action of a converging lens. Pinholes in aluminum foil each project a separate image of the lamp filament; placing a large lens in the path brings all images to a single focus point, showing how a lens collects and redirects diverging light.
Figure 1:
Complete setup: variac, lamp with housing on stand, aluminum foil and push pins for creating pinholes, and white poster board as projection screen.
Figure 2:
Aluminum foil covers the lamp tube opening with small holes punched through, each acting as a point source that projects an image of the filament.
Figure 3:
Without the lens, each pinhole projects a separate inverted image of the lamp filament onto the screen.
Figure 4:
With the large lens in place, the filament images converge to a common focus with visible chromatic aberration (rainbow fringing).
Equipment
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