The device known when electrons are emitted when light shines on a metal surface is called a photoelectric cell or phototube.

Here's a breakdown:

* Photoelectric Effect: This is the fundamental phenomenon where light (photons) interact with the electrons in a metal, providing enough energy to eject them from the metal's surface.

* Photoelectric Cell: This is a device that utilizes the photoelectric effect. It consists of a metal cathode (emitting electrons) and an anode (collecting electrons) inside an evacuated glass tube. When light falls on the cathode, electrons are emitted and collected by the anode, producing a measurable current.

Photoelectric cells have various applications, including:

* Light detection: They are used in light meters, smoke detectors, and automatic door openers.

* Solar cells: These are photoelectric cells specifically designed to convert sunlight into electricity.

* Image sensors: They are used in digital cameras, video cameras, and other imaging devices.

Let me know if you have any more questions!