Cl10 light reflaction and refraction
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Transcript of Cl10 light reflaction and refraction
LIGHT-REFLACTION AND REFRACTION
SUB TOPIC- REFLECTIONPrepared by- Mrs.Priya Jha
Light • Our primary source of light is the sun.• Light travels in straight lines at a speed of
186,000miles per second.• *Light waves travel faster than sound waves!• Light energy from the sun travels through
space , reaches earth, and some of it turns to heat energy and warms the earth’s air.
• Light from the sun also travels to the cells of green plants (producers) and is stored as energy.
• When light reaches an object, it is absorbed, reflected, or passes through it.
What is light really?Electromagnetic radiation waves
• Light waves are three dimensional.
• Light waves vibrate in all planes around a center line.
• The waves have high points called “crests.”
• Waves also have low points called “troughs.”
• *The distance from one crest to the next crest is called a “wavelength.”
• *The number of waves passing a given point in one second is called the “frequency.”
wavelength
Essential Knowledge, Skills, and Processes
• Diagram and label a representation of a light wave (wavelength, peak, trough)
We will investigate the following:
• Reflection of light• Spherical mirrors• Images formation by spherical mirrors• Representation of images formed by
spherical mirrors using ray diagrams• Mirror formula and magnification
Reflection of light
• Reflection – Bouncing back of light waves
. The laws of reflection are as follows
• The incident ray, the reflected ray and the normal to the reflection surface at the point of the incidence lie in the same plane.
• The angle which the incident ray makes with the normal is equal to the angle which the reflected ray makes to the same normal.
• The reflected ray and the incident ray are on the opposite sides of the normal.
- Reflection• Reflection from a mirror:
Incident ray
NormalReflected ray
Angle of incidence
Angle of reflection
Mirror
Angle of incidence
Angle of reflection
• The Law of ReflectionThe Law of Reflection
Angle of incidence = Angle of Angle of incidence = Angle of reflectionreflection
The same !
!!
The same !!!
Mirror
LIGHT & ITS USES: Mirrors
• Plane Mirrors – Perfectly flat– Virtual – Image is “Not Real” because it
cannot be projected
– Erect – Image is right side up
© 2000 Microsoft Clip Gallery
LIGHT & ITS USES: Mirrors
• Reflection & Mirrors (Cont.)– Convex Mirror
• Curves outward• Enlarges images.
– Use: Rear view mirrors, store security…
CAUTION! Objects are closer than they appear!© 2000 Microsoft Clip Gallery
Light & Its Uses: Mirrors
• Reflection Vocabulary– Optical Axis – Base line through the center
of a mirror or lens– Focal Point – Point where reflected or
refracted rays meet & image is formed– Focal Length – Distance between center of
mirror/lens and focal point
© 2000 Microsoft Clip Gallery
Spherical mirrors
• A curved mirror is a mirror with a curved reflective surface, which may be either convex (bulging outward) or concave (bulging inward). Most curved mirrors have surfaces that are shaped like part of a sphere, but other shapes are sometimes used in optical devices. The most common non-spherical type are parabolic reflectors, found in optical devices such as reflecting telescopes that need to image distant objects, since spherical mirror systems suffer from spherical aberration.
Curved mirror• A curved mirror can be thought of as
consisting of a very large number of small plane mirrors oriented at slightly different angles. The laws of reflection always apply, regardless of the shape or smoothness of the surface
Spherical mirror• A spherical mirror consists of a portion of
a spherical surface.• A converging mirror has a concave
reflecting surface. • A diverging mirror has a convex
reflecting surface.
Rules for drawing ray diagrams for converging and diverging mirrors:
• (Parenthetical remarks refer specifically to diverging mirrors. Rules 1 and 2 apply to parabolic mirrors only.)
• An incident ray that is parallel to the principal axis is reflected such that it passes through the principal focus (or appears to have originated at the principal focus).
• An incident ray passing through (or heading toward) the principal focus is reflected such that it travels parallel to the principal axis.
• An incident ray passing through (or heading toward) the centre of curvature reflects back along the same path.
Rules of Reflection for Curved Mirrors
• 1. Any light ray traveling parallel to the principal axis is reflected by the curved mirror through the principal focus.
It either actually passes (for a concave mirror) or appears to pass (for a convex mirror) through the principal focus.
• 2. Any light ray that passes (for a concave mirror) or appears to pass (for a convex mirror) through the principal focus is reflected by the curved mirror parallel to the principal axis.
• 3. Any light ray that passes (for a concave mirror) or appears to pass (for a convex mirror) through the center of curvature retraces its initial path after reflection by the curved mirror.
• 1. Any light ray traveling parallel to the principal axis is reflected by the curved mirror through the principal focus.
It either actually passes (for a concave mirror) or appears to pass (for a convex mirror) through the principal focus.
FocusC
PRINCIPAL AXIS
i
r
• Any light ray that passes (for a concave mirror) or appears to pass (for a convex mirror) through the principal focus is reflected by the curved mirror parallel to the principal axis.
F
• Any light ray that passes (for a concave mirror) or appears to pass (for a convex mirror) through the center of curvature retraces its initial path after reflection by the curved mirror.
C F
Types of spherical mirror
Centre of Curvature : The centre of curvature of a curved mirror isdefined as the center of the hollow glass sphere of which the curvedmirror was (previously) a part.Radius of curvature :The radius of curvature of a curved mirror isdefined as the radius of the hollow glass sphere of which thespherical mirror was (previously) a part. Note that any line drawn fromthe center of curvature C to the mirror surface meets it at rightangle and equals the radius of curvature.Principal Axis :The principal axis of a curved mirror is defined as theimaginary line passing through its pole P and center of curvature C.Focus :The principal focus is defined as the point on the principal axiswhere the light rays traveling parallel to the principal axis afterreflection actually meet (for a concave mirror) or appear to meet (for aconvex mirror).
Parts of a spherical mirror
The principal focus is in front of the concave mirror and is behind the convex mirror.The focal length (denoted by FP in the figure) is the distancebetween the pole P and the principal focus F of a curved mirror. Focal length is half the radius of curvature.Focal Length = Radius of Curvature/2Pole : The pole is defined as the geometric center of the curved mirror.
Convex mirrors
• A convex mirror, fish eye mirror or diverging mirror, is a curved mirror in which the reflective surface bulges toward the light source. Convex mirrors reflect light outwards, therefore they are not used to focus light
Convex mirror• A convex mirror, fish eye mirror or diverging
mirror, is a curved mirror in which the reflective surface bulges toward the light source. Convex mirrors reflect light outwards, therefore they are not used to focus light. Such mirrors always form a virtual image, since the focus (F) and the centre of curvature (2F) are both imaginary points "inside" the mirror, which cannot be reached. As a result, images formed by these mirrors cannot be projected on a screen, since the image is inside the mirror
Effect on image of object's position relative to mirror focal point (convex)
Object's position (S),focal point (F)
Image Diagram
VirtualUprightReduced (diminished/smaller)
Mirror Ray Tracing
• Mirror ray tracing is that rays parallel to the optic axis and through the focal point are used. A third useful ray is that through the center of curvature since it is normal to the mirror and retraces its path backward.
Concave mirrors • A concave mirror, or
converging mirror, has a reflecting surface that bulges inward (away from the incident light). Concave mirrors reflect light inward to one focal point.They are used to focus light. Unlike convex mirrors, concave mirrors show different image types depending on the distance between the object and the mirror.
Effect on image of object's position relative to mirror focal point (concave)
Object's position (S),focal point (F)
Image Diagram
S < F(Object between focal point and mirror
VirtualUprightMagnified (larger)
Effect on image of object's position relative to mirror focal point (concave)
Object's position (S),focal point (F)
Image Diagram
S = F(Object at focal point)
Reflected rays are parallel and never meet, so no image is formed.In the limit where S approaches F, the image distance approaches infinity, and the image can be either real or virtual and either upright or inverted depending on whether S approaches F from above or below.
Effect on image of object's position relative to mirror focal point (concave)
Object's position (S),focal point (F)
Image Diagram
F < S < 2F(Object between focus and centre of curvature)
RealInverted (vertically)Magnified (larger)
Effect on image of object's position relative to mirror focal point (concave)
Object's position (S),focal point (F)
Image Diagram
S = 2F(Object at centre of curvature
RealInverted (vertically)Same sizeImage formed at centre of curvature
Effect on image of object's position relative to mirror focal point (concave)
Object's position (S),focal point (F)
Image Diagram
S > 2F(Object beyond centre of curvature)
RealInverted (vertically)Reduced (diminished/smaller)
Image Characteristics
• The image characteristics found in a converging mirror depend on the location of the object. The table below summarizes the characteristics of images found in a converging mirror based on the location of the object:
Object location
Magnifi-cation
Attitude Type Position
near infinity
< -1 Inverted real at F
beyond C
< -1 Inverted real between F & C
at C -1 Inverted real at C
between F and C
> -1 Inverted real beyond C
between F and V
> +1 erect virtual behind mirror
at F undefined
Sign convention for Reflection by Spherical Mirrors
New Cartesian Sign Convention
New Cartesian Sign Convention
XX’
Y
Y’
(+x, +y)(-x, +y)
(-x, -y)(+x, -y)
Convex Mirror Image
Concave Mirror Image
i. The object is always placed to the left of the mirror. This implies that the light from the objects falls on the from the left-hand side.
ii. All distance parallel to the principal axis are measured from the pole of the mirror.
iii. All the distance measured to the right of the origin (along +x-axis ) are taken as positive while those measured to the left of the origin (along -x-axis) are taken as negative.
iv. Distance measured perpendicular to and above the principal axis (along +y-axis) are taken as positive.
v. Distance measured perpendicular to and below the principal axis (along -y-axis) are taken as negative.
Mirror equation and magnification
• Gaussian form• The Gaussian mirror
equation relates the object distance =do and
• image distance =di to
• the focal length= f:
• The magnification of a mirror is defined as the height of the image divided by the height of the object:
By convention, if the resulting magnification is positive, the image is upright. If the magnification is negative, the image is inverted (upside down).
Mirror Equations• 1/f = i/do + 1/di• Magnification (M) = di/do
• f – Focal length of the mirror• di Distance of the image from the Pole
• Mirror Equations• *f is +ve in the case of concave mirror.• *f is ve• in the case of a convex mirror.• * di is +ve if the image is a real image and located on the
object's side of the mirror.• * di is ve if the image is a virtual image and located• behind the mirror
power of mirrors and lenses (in dioptres):
where f (metre) is the focal length.
(Some texts use D for the power)
curved mirror and lens equation:
,since
(The equations apply for mirrors and lenses. The derivation of the equations using similar triangles is optional.)
Sign conventions for the use of the lens equations:
• The focal length (f) is positive for converging mirrors and lenses, and negative for diverging ones.
• The object distance (do) is positive. (The distance is negative for a virtual object.)
• The image distance (di) is positive for all real images and negative for virtual images.
• Heights (Ho and Hi) are positive if measured upward from the principal axis and negative if measured downward.
• Magnification (m) is positive if the image is erect and negative when inverted.
Uses of Convex mirror• Convex mirror lets motorists see around a corner.• The passenger-side mirror on a car is typically a convex mirror. In
some countries, these are labeled with the safety warning "Objects in mirror are closer than they appear", to warn the driver of the convex mirror's distorting effects on distance perception. Convex mirrors are preferred in vehicles because they give an upright, though diminished, image. Also they provide a wider field of view as they are curved outwards.
• Convex mirrors are used in some automated teller machines as a simple and handy security feature, allowing the users to see what is happening behind them. Similar devices are sold to be attached to ordinary computer monitors.
• Some camera phones use convex mirrors to allow the user to correctly aim the camera while taking a self-portrait.
• Light travels VERY FAST – around 300,000 kilometres per second.
At this speed it can go around the world 8 times in one second.
