Determine a relationship between the number of images formed by two plane mirrors and the value of the angle between these two mirrors, on the basis of observations in the laboratory.
The appearance of multiple images is caused by a succession of reflections between two mirrors.
Let's examine in further detail the case of images formed by two plane mirrors placed at 90 degrees to one another.
Locate the images of the object in each of the mirrors (primary images).
Extend the line of the mirrors' positions (broken lines on the diagram).
Treating the primary images as objects in front of the mirror extension lines:
- Draw a perpendicular to one of the mirror extension lines.
- Measure the distance from the primary image to the mirror extension line.
- Locate the secondary image at an equal distance along the perpendicular.
- Repeat the last three steps to locate the image of the other primary image.
In the case of mirrors at a right angle, only one secondary image is formed:
By decreasing the angle between the mirrors, the number of images is increased. When an object is placed in front of two plane mirrors, the number of images formed varies inversely to the angle between the two mirrors. Two mirrors placed at 90 degrees to one another will form 3 images of the same object, namely:
2 primary images seen as a result of a single reflection of the rays.
1 secondary image seen as a result of a double reflection of the rays.
Two mirrors facing one another will produce a large number of images. This number is limited because light is absorbed by the multiple reflections. The images can be identified by their apparent distance. Secondary images appear further away than primary images, since light must travel a greater distance in a double reflection than in a single reflection.
