Introducing a Pinhole - Physics Demonstrations - Introducing a Pinhole | Physics Undergraduate Labs

Purpose

A sequential progression from shadow casting through slit projection to pinhole imaging. Students build intuition for rectilinear propagation, image inversion, and the pinhole camera principle by drawing ray diagrams at each step.

Full setup: translucent screen at left, multicolor LED tower on stand at center, incandescent light bulb in wooden box at right, with bar clamp, lead brick, and masks on bench

Two flashlights clamped to a ring stand at left, dark rectangular mask propped upright with a white-painted lead brick, translucent screen at right, flashlight caps on bench

Translucent screen showing a bright central band where both flashlights illuminate, with dimmer bands above and below where only one flashlight reaches

Two thin horizontal blue-white lines on a dark screen, projected through the slit mask from dual flashlights

Colored horizontal lines on dark screen — violet, green, and red/orange — projected from LED tower through slit mask

Vertical column of colored dots on dark screen — violet, blue, green, yellow, red from top to bottom — projected from LED tower through pinhole

Glowing orange coiled filament image projected through pinhole onto dark screen, showing the inverted filament structure of the incandescent bulb

Figure 1: Complete demonstration setup showing the translucent screen (left), LED tower for creating colored point sources, and light bulb box for demonstrating filament imaging through the pinhole.

Figure 2: Alternate view showing the flashlight arrangement and mask positioning used in the initial shadow demonstration phase of the sequence.

Figure 3: Screen image showing overlapping rectangular shadows from dual flashlight sources through the rectangular mask, demonstrating basic shadow formation and light blocking.

Figure 4: Slit mask projection showing two bright lines from the dual flashlight sources, demonstrating the inverted geometry where upper flashlight creates lower line and vice versa.

Figure 5: LED tower light passing through slit mask creating multiple colored lines, one for each LED source, demonstrating how different point sources create distinct images at different positions.

Figure 6: Pinhole projection of LED tower showing inverted vertical array of colored dots, demonstrating true pinhole imaging where each point source creates a distinct inverted image point.

Figure 7: Inverted image of incandescent bulb filament projected through pinhole, showing clear extended-object imaging with visible coil structure demonstrating the pinhole camera principle.

Pinhole Mask

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