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Archimedes's Death RayFor centuries, it was rumoured that the Greek scientist, Archimedes, used a "burning glass" to focus the sun’s rays on an invading Roman fleet which was attacking his home town of Syracuse around 214 B.C. Frompg 65 The Flying Circus of Physics by Jearl Walkers
Archimedes's Death RayFor centuries, it was rumoured that the Greek scientist, Archimedes, used a "burning glass" to focus the sun’s rays on an invading Roman fleet which was attacking his home town of Syracuse around 214 B.C. Frompg 65 The Flying Circus of Physics by Jearl Walkers
Archimedse's Death RayFor centuries, it was rumoured that the Greek scientist, Archimedes, used a "burning glass" to focus the sun’s rays on an invading Roman fleet which was attacking his home town of Syracuse around 214 B.C. Frompg 65 The Flying Circus of Physics by Jearl Walkers
Archimedes's Death RayThe way that this feat may have been possible was to use many plane mirrors. (Greek soldiers had copper shields which could be highly polished.)Frompg 65 The Flying Circus of Physics by Jearl Walkers
Archimedes's Death RayEach mirror could be used to reflect a spot of sunlight at the same object (invading Roman ship). Frompg 65 The Flying Circus of Physics by Jearl Walkers
Archimedes's Death RayThis might act like a giant magnifying glass. Frompg 65 The Flying Circus of Physics by Jearl Walkers
Archimedes's Death RayThis might act like a giant magnifying glass and ignite the target. Frompg 65 The Flying Circus of Physics by Jearl Walkers
Archimedes's Death RayThe historical record of this possible event is very weak. It is argued that the feat was impossible given the technology available to Archimedes. Frompg 65 The Flying Circus of Physics by Jearl Walkers
Archimedes's Death RayThere is also a problem in aiming all the mirrors at the target with this. Frompg 65 The Flying Circus of Physics by Jearl WalkersWhat technique would have to be used for aiming the mirrors at distant objects?
Could it be done today?http://www.youtube.com/watch?v=MDkOaPp_6ug Click on Image to play Archimedes’s Death Ray Myth Busters Eat Your Heart Out
The mirrors can be aligned along a smooth curve so that they still all reflect light from the sun to the same spot.When light rays come from a distant source like the sun, they can be considered parallel.
All incident light rays which are parallel to each other will reflect off any part of the smooth curve and pass through the same spot.This spot is called the Focus.
The Curve is called a Parabola.The symbol for the Focus is (F).Unfortunately, Parabolic mirrors are expensive to make.
A circle can be drawn so that it closely matches the parabola near the central region.Fortunately, Circular (or in 3D, Spherical) mirrors are less expensive to make. The symbol “C” stands for Centre of Curvature of the Spherical mirror.
Most curved mirrors that are used have a Spherical instead of the more expensive (but better) Parabolic shape.Only a small portion of the Spherical mirror is used so that it closely matches the properties of a Parabolic mirror.
The inside of a sphere produces a concave mirror. The outside produces a convex mirror.
The Parts of a Concave Mirror C Centre of Curvature F Focus f Focal Length V Vertex
Concave Mirror Characteristic Rays Concave mirrors can produce images but they are more complicated than plane mirrors.
Concave Mirror Characteristic Rays Certain light rays called “Characteristic Rays” always reflect the same way from a Concave mirror . These Characteristic Rays can be used to predict what the images will look like.
Concave Mirror Characteristic Rays Any incident ray parallel to the principal axis will……
Concave Mirror Characteristic Rays Any incident ray parallel to the principal axis will reflect through the Focus.
Concave Mirror Characteristic Rays Any incident ray passing through the Focus will……
Concave Mirror Characteristic Rays Any incident ray passing through the Focus will reflect parallel to the principal axis.
Concave Mirror Characteristic Rays Any incident ray passing through the Centre of Curvature will……
Concave Mirror Characteristic Rays Any incident ray passing through the Centre of Curvature will reflect back upon itself.
Concave Mirror Characteristic Rays Any incident ray striking the Vertex will……
Concave Mirror Characteristic Rays Any incident ray striking the Vertex will reflect such that i =r.
Predicting Images in a Concave Mirror Any incident ray parallel to the principal axis will……
Predicting Images in a Concave Mirror Any incident ray parallel to the principal axis will reflect through the Focus.
Predicting Images in a Concave Mirror Any incident ray passing through the Focus will……
Predicting Images in a Concave Mirror Any incident ray passing through the Focus will reflect parallel to the principal axis.
Predicting Images in a Concave Mirror Any incident ray striking the Vertex will reflect such that i =r.
Predicting Images in a Concave Mirror Where is the image?
Predicting Images in a Concave Mirror The object is located where the rays appear to come from.
Predicting Images in a Concave Mirror The image is also located where the rays appear to come from.
NOTE: Light rays originating from any point on the object, and reflecting off the mirror, will pass through a corresponding point on the image. Characteristic rays simply help predict image location and characteristics.
NOTE: The bottom of the object could be below the principal axis. The bottom of the image would be found the same way as the top. For simplicity, we place the bottom of the object on the principal axis.
Predicting Images in a Concave Mirror Your Turn Continue with Concave Mirrors - Handouts
Predicting Images in a Concave Mirror Object is at the Centre of Curvature.
When the Object is at C Any incident ray parallel to the principal axis will……
Any incident ray parallel to the principal axis will reflect through the Focus.
Any incident ray passing through the Focus will reflect parallel to the principal axis.
Any incident ray striking the Vertex will reflect such that i =r.
