Greer's class watches a movie thrown onto a screen by a projector. The picture really lands on the screen: the screen catches it. Could every image be caught like that?
An image is a picture that light builds of an object. This lesson gives the one test that sorts every image in this topic into two kinds: try to catch it on a screen.
Light rays from the projector cross at the screen: at each point of the picture, rays actually meet.
Where rays actually meet, a screen placed there catches the picture.
An image formed where the rays actually meet is called a real image.
A screen placed at a real image shows the picture.
Sometimes the rays never meet: they leave a surface spreading apart.
Spreading rays can still look as if they all come from one point.
An image the rays only appear to come from is called a virtual image.
A screen placed where a virtual image appears to be catches nothing, because no light arrives there.
Elowen makes a viewer from a shoebox: a tiny hole in the front, and thin white paper as the back wall. An upside-down picture of the window appears on the paper. Is the image real or virtual?
The paper is a screen, and the picture lands on it.
A screen can catch a picture only where rays actually meet.
So the rays from the window actually meet at the paper.
The image is real.
Rays of light leave a sheet of glass spreading apart, as if they all came from one point behind the glass. Fintan holds a white card at that point. What does the card show, and which kind of image is this?
The rays spread apart after the glass; they never meet.
No light travels to the point behind the glass that they appear to come from.
A card held there catches no light.
The card shows nothing: the image is virtual.
At an outdoor movie night, a projector throws a sharp picture onto a white bedsheet. Is the picture on the bedsheet a real image or a virtual image?
A white card is held at the place where a virtual image appears to be. What does the card show?
Haldis says: 'If a picture can be caught on a screen, the rays of light actually meet at the screen.' Is Haldis correct?
Which statement gives the difference between a real image and a virtual image?
Fintan points a projector at a screen and slides the screen slowly backward, and the picture blurs. At the screen's first, sharp position, what was true of the light rays?
An image of a lamp seems to sit at a spot in the air near a glass door, but a notebook held at that spot stays dark. By the screen test, which kind of image is it?