Curved Mirrors: Concave
Applied Physics and Chemistry
Reflection Lecture 2
Curved mirrors
• What if the mirror isn’t flat?
– light still follows the same rules, with local
surface normal
• Parabolic mirrors have exact focus
– spherical mirrors may experience distortion
– used in telescopes, backyard satellite dishes,
etc.
– also forms virtual image
education.jlab.org/powerpoint/0708_optics_mirrors_and_lenses.ppt
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82a425d7
Concave Mirrors
• Curve inward
• May be real or virtual image
education.jlab.org/powerpoint/0708_optics_mirrors_and_lenses.ppt
Concave Mirror
• The center C of a concave mirror is outside the
mirror.
• Focal point F is also outside the mirror, half way
between the center and the surface of the mirror.
• The focal length f is half of the radius of curvature.
www.physics.umd.edu/courses/Phys106/FL11.ppt
Image from a concave mirror: case 1
Step 1
Step 3
Step 2
Step 4
www.physics.umd.edu/courses/Phys106/FL11.ppt
Image from a concave mirror: case 1
www.physics.umd.edu/courses/Phys106/FL11.ppt
Properties of the Image
• If we put an object outside of the center of a
concave mirror, we find the image is
– Real, in the sense that all light rays pass through
the image.
– Inverted, in the sense that the direction of the
arrow has been changed.
– The image is smaller!
www.physics.umd.edu/courses/Phys106/FL11.ppt
Animation for case 1
www.physics.umd.edu/courses/Phys106/FL11.ppt
Image for a concave mirror: case 2
www.physics.umd.edu/courses/Phys106/FL11.ppt
• If the object is in between the center and the
focal point, the image is
– Real
– Inverted
– Magnified in the sense that the image is bigger
than the real object.
www.physics.umd.edu/courses/Phys106/FL11.ppt
Animation for case 2
www.physics.umd.edu/courses/Phys106/FL11.ppt
Image from a concave mirror: case 3
www.physics.umd.edu/courses/Phys106/FL11.ppt
Image from a concave mirror: case 3
www.physics.umd.edu/courses/Phys106/FL11.ppt
Animation for case 3
www.physics.umd.edu/courses/Phys106/FL11.ppt
Properties of the image
• If the object is closer to the mirror than the
focal point F, the image is
– Virtual, it is behind the mirror
– Upright, not inverted
– Magnified
www.physics.umd.edu/courses/Phys106/FL11.ppt
Java Applet
• http://www.microscopy.fsu.edu/primer/java/
mirrors/concave.html