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How does a camera shutter control exposure time?

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Diagram showing the negative-positive photographic process: a scene is captured on film in a camera, developed into a negative, projected onto paper with an enlarger, and developed again to produce a positive print. — technology of photography Figure 1: Sequence of negative–positive process, from the photographing of the original scene to enlarged print (see text).

A camera shutter controls exposure time by regulating the duration that light is permitted to reach the film or electronic image sensor. By adjusting this shutter speed, a photographer can manage how much light enters the camera and determine the ability to "freeze" motion.12

Modern cameras primarily utilize two mechanical systems to achieve this:

Leaf Shutter: Located near the lens, this device uses overlapping metal blades that open and close to admit light for a specific duration.1
Focal-plane Shutter: Positioned directly in front of the image plane, this consists of two blinds that create a traveling slit. The width of this slit determines the exposure time; a narrower slit results in a shorter exposure, as the blinds move across the frame in succession.13

Additionally, some digital cameras use electronic shutters that toggle the sensor's light-reading capability on and off to capture an image.1