Plane Mirror Applications PW2 – Reflection

1) Multiple Mirrors Two mirrors set at right angles produce three virtual images. Image 1 comes from mirror 1 while image 2 comes from mirror 2. Image 3 comes from some of the light that is reflected twice (from mirror 2, then mirror 1, then back to the eye).

*Images From 2 Mirrors at Right Angles To find how the eye sees all 3 images: Find image1 behind mirror1 using a perpendicular and making do = di. Find image2 behind mirror2 using a perpendicular and do = di. From image1, draw a dotted line parallel to mirror1. From image2, draw a dotted line parallel to mirror2. Image3 is located where the two dotted lines intersect. Draw a straight line from image3 to the top and bottom of the eye. Remember to use dotted lines behind the mirrors.

*Images From 2 Mirrors at Right Angles From the "image3 to eye" lines that intersect mirror1, draw lines toward image2 behind mirror2. From the intersection points on mirror2, draw lines back to the object. Draw arrows indicating that the light rays go from the object to mirror2, then to mirror1, and finally to the eye. This is how the eye sees image3. The light rays reflect off both mirrors.

Multiple Mirrors If two mirrors are set at angles less than 90o, then several images are produced. Clothing stores and hair salons often use two or three mirrors to produce a variety of images. Finding Images Mathematically When 2 mirrors are set up at an angle less than 90o, you can use the following formula to determine how many images will be seen.

Multiple Mirrors Example If the angle between two mirrors is 60o, how many images will you see? You will see 5 images.

2) Periscope A simple periscope has two plane mirrors set up at 45o angles to each other. The light from an object strikes the top mirror, reflects down to the bottom mirror and on to the eye. The image from the top mirror is laterally reversed, but the bottom mirror reverses the image from the top mirror – the end result being an image that is normal, no reversal.

*Images in a Simple Periscope To find the images and show how the eye sees through a simple periscope do the following: Extend mirror 1 and 2 Find the image behind mirror 1 by drawing a perpendicular and making do = di.

*Images in a Simple Periscope Extend the perpendicular down beyond mirror 2 (extended). Measure along the perpendicular from mirror 2 (extended) to image 1. This distance becomes the do for mirror 2. Make do = di for mirror 2 to find image 2. From image 2, draw ray lines back to top and bottom of eye. (Remember to use dotted lines behind the mirror.) Where ray lines meet mirror 2, draw lines up to image 1. Where ray lines meet mirror 1, draw lines to object. Finally, put arrows on ray lines to show direction of light.

3) Cameras Plane mirrors are often used with viewfinders of SLR (single lens reflex) cameras. The mirror is right behind the lens. The light passes through the lens, reflects off several mirrors and then goes through the viewfinder. When the shutter is released, the mirror flips out of the way so the light can strike the film.