Lecture 36: FRI 17 APRGeometrical OpticsPlane MirrorsPowerPoint PresentationSlide 5Slide 6Spherical mirrorsImages from spherical mirrorsSlide 9Slide 10Slide 11ExampleSlide 13Hubble, Hubble, Toil and TroubleSlide 15Lecture 36: FRI 17 APRLecture 36: FRI 17 APRPhysics 2102Jonathan Dowling34.1–4: Geometrical Geometrical opticsopticsQuickTime™ and a decompressorare needed to see this picture.QuickTime™ and a decompressorare needed to see this picture.QuickTime™ and a decompressorare needed to see this picture.QuickTime™ and a decompressorare needed to see this picture.Geometrical OpticsGeometrical Optics• “Geometrical” optics (rough approximation): light rays (“particles”) that travel in straight lines.• “Physical” Classical optics (good approximation): electromagnetic waves which have amplitude and phase that can change. • Quantum Optics (exact): Light is BOTH a particle (photon) and a wave: wave-particle duality.Plane MirrorsPlane MirrorsLight rays reflect on a plane mirror, and produce a virtual image behind the mirror. What’s a virtual image? It means the light rays are NOT coming from a real point, there is no light where the image appears.i= -p for a plane mirrorobjectimageQuickTime™ and a decompressorare needed to see this picture.Ray Tracing Plane (Flat) Mirror• Draw Perpendicular Line to Mirror From Each Point.• Use i=r To Draw Reflected Rays to Eye. • Draw Two Rays From Object to Point on Mirror.• Extend Reflected Rays Behind Mirror to Find Virtual ImageQuickTime™ and a decompressorare needed to see this picture.Ray Tracing Plane (Flat) MirrorImage distance is minus Object distance, do?=?–di , means image is behind (minus) the mirror and | do?|=?|di| means image is behind mirror same distance object is in front.Virtual image means no light actually is at the image location (optical illusion). Magnification m?=?+1 means image has same height as object (|m|=1) and image is right-side up (m is plus). hohi=+ho?=?–dom?=?ho/hi?=?+1Spherical mirrorsSpherical mirrors• Focal point is at half the curvatuire radius: f= - r/2 .•Rays parallel to the axis, reflect through the focal point.• Rays hitting the mirror after going to the focal point, emerge parallel.• Rays going through the center of curvature, reflect back on themselves.Concave mirrors: r > 0 Convex mirrors: r < 0Images from Images from spherical mirrorsspherical mirrorsfip111=+Consider an object placed between the focal point and the mirror. It will produce a virtual image behind the mirror.When the object is at the focal point the image is produced at infinity.If the object is beyond the focal point, a real image forms at a distance i from the mirror.Check the signs!!pim −=lateralmagnificationRay Tracing Concave Mirror: Image Outside Focal Point• Ray Through Focal Point Bounces into Horizontal• Image is Real (Light At Image), Inverted, and Shrunk (m=ho/hi is minus and |m|< 1) and do and di are both positive (to left) • Horizontal Ray Bounces Through Focal Point• Ray Through Center Bounces Straight Back At’cha! • Rays Cross at Image Point QuickTime™ and a decompressorare needed to see this picture.Ray Tracing Concave Mirror: Image Inside Focal Point• Ray Through Focal Point Bounces into Horizontal• Image is Virtual (no light), Upright, and Enlarged (m=ho/hi is plus and > 1) And do = + and di = – are on opposite sides of mirror. • Horizontal Ray Bounces Through Focal Point• Ray Through Center Bounces Straight Back At’cha! • Project Behind Mirror to Cross at Virtual Image QuickTime™ and a decompressorare needed to see this picture.Ray Tracing Convex Mirror• Ray Towards Focal Point Bounces into Horizontal• Image is Virtual (no light), Upright, and Shrunk (m=ho/hi is plus and < 1) And do = + and di = – are on opposite sides of mirror. • Horizontal Ray Bounces Into Line of Focal Point• Ray Towards Center Bounces Straight Back At’cha! • Project Rays Behind Mirror Cross at Virtual ImageQuickTime™ and a decompressorare needed to see this picture.ExampleExampleAn object 2cm high is located 10cm from a convex mirror with a radius of curvature of 10cm. Locate the image, and find its height. Focal length: f= r/2= -10cm/2= -5cm.Image position: 1/i=1/f-1/p= -1/5cm –1/10cm= -3/10cm i= - 10/3cm = -3.33 cm: the image is virtual.Magnification: m= -i/p= - (-3.33cm)/(10cm)=+0.33 (upright, smaller).If the object image is 2cm, the image height is 0.33 x 2cm=0.67 cm.QuickTime™ and a decompressorare needed to see this picture.Newton’s Reflecting TelescopeHubble, Hubble, Toil and Hubble, Hubble, Toil and TroubleTroubleHubble mirror screw up: The central region of the mirror was flatter than it should be - by just one-fiftieth of the width of a human hair. This is equivalent to only four wavelengths of visible light, but it was enough. One insider said that the Hubble mirror was "very accurate, very accurately the wrong shape". A star seen with a ground telescope and with “old” HubbleThe same star seen with the “new” HubbleBefore and after...QuickTime™ and a decompressorare needed to see this picture.QuickTime™ and a decompressorare needed to see this picture.QuickTime™ and a decompressorare needed to see this picture.QuickTime™ and a decompressorare needed to see this
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