Una aims an ultraviolet lamp at a freshly cleaned zinc plate. The instant the lamp lights, something invisible starts leaving the metal. The plate is losing electrons.
In the electromagnetic waves topic, you saw the evidence that light travels as a wave, an electromagnetic one. In the circuits topic, you saw that a metal is full of free electrons, electrons that can leave their atoms and move about inside the metal. This lesson shows what light can do to those electrons.
Light shining on a metal surface can knock electrons out of the metal.
The light arrives at the surface, and electrons leave it.
Ultraviolet light on a freshly cleaned zinc plate ejects electrons from the zinc.
Each ejected electron leaves the metal completely; it is not just moved around inside.
The name says what happens: photo for the light that arrives, electric for the electrons it ejects.
The next lessons measure when the effect happens and when it refuses to happen.
A clean sodium plate sits in a dark room. An ultraviolet lamp pointed at the plate is switched on. What can the light do to the plate?
Light shining on a metal surface can knock electrons out of the metal.
The lamp's ultraviolet light lands on the sodium surface.
So the light can eject electrons from the sodium.
The light can knock electrons out of the sodium plate. That is the photoelectric effect.
Vasco covers half of a lit zinc plate with an opaque card. From which part of the plate are electrons ejected?
Only light that reaches the metal can knock electrons out of it.
The card blocks the light before it reaches the covered half.
The uncovered half still receives the light.
Electrons are ejected only from the uncovered half of the plate.
An ultraviolet lamp shines on a freshly cleaned iron plate. What can the light knock out of the metal?
Vasco says: 'In the photoelectric effect, light shining on a metal knocks electrons out of the metal's surface.' Is Vasco correct?
In the photoelectric effect, what arrives at the metal and what leaves it?
Which of the following is an example of the photoelectric effect?
A museum cleans an old silver tray until its surface is bare metal, then lights it with a strong ultraviolet lamp. What does the photoelectric effect say the light can do?
Light shining on a metal knocks electrons out of the metal's surface. What is this effect called?