Light is a form of energy that could be obtained from a luminous source or reflected off a non-luminous source into our eyes. When a ray of light strikes any surface, it will reflect and changes its direction of travel.
Terms used for reflection of light:
Incident ray: ray of light that strikes the surface
Reflected ray: Ray of light that is reflected off the surface
Normal: Imaginary line that is perpendicular to the surface at the point of incidence
Angle of Incidence: angle between the incident ray and the normal
Angle of Reflection: angle between the normal and the reflected ray
Laws of Reflection:
1) The incident ray, reflected ray, and the normal at the point of incidence all lie in the same plane
2) Angle of incidence = Angle of reflection
Differences between specular reflection and diffused reflection:
1) A specular reflection is all reflected in the same direction while a diffused reflection is reflected in different directions.
2) A specular reflection reflects on smooth surfaces while a diffused reflection reflects on rough surfaces.
3) A specular reflection results in a clear image formed while a diffused reflection results in a blur image formed.
Notes:
-All reflected rays and incident rays are to be drawn in solid lines, while working lines such as the normal is to be drawn in dotted lines.
-When drawing the reflected rays and incident rays, an arrowhead must be present to indicate the direction of a particularly light ray.
-Always use pencil to draw ray diagrams and protractor to ensure the normal is perpendicular to the surface
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Ray Diagram drawing for Reflection:
Every ray that is reflected off the mirror always follows the law of reflection (angle of incidence = angle of reflection). The image behind the mirror is virtual because light rays do not actually pass through the image and it could not be captured by a screen.
Steps for drawing ray diagram:
1) Draw a similar image in the mirror (Refer to the segment on image characteristics below to know the points to take note of when drawing images)
2) Draw 2 light rays from a point of the virtual image to the eye
3) Draw 2 solid light rays from the real object to the points of reflected rays on the mirror.
4) Draw the arrowheads to indicate the direction (Object -> mirror -> Observer)
Notes:
1) Always use ruler to measure the distance between the mirror and the object to ensure an accurate diagram
2) Use solid lines in front of the mirror and dotted lines behind the mirror and for working lines
Image characteristics of a Mirror
The image that we see on the mirror is formed when the light rays reflect off you, strike the mirror, and eventually travel to your eyes.
Characteristics of an image formed in plane mirror:
1) Same size as the object
2) Same distance behind the mirror as the object is in front of the mirror
3) Same orientation as the object, Ex, both the object and the image is upright
4) Laterally inverted
5) Virtual
Images formed in different types of mirror:
-Plane mirror:
Object position: Anywhere
Image position: on the opposite side of the mirror as the object/ same distance behind the mirror as the object is in front of it
Type of image: Virtual
Orientation of image: Same as object
Size of Image: Same as object
-Concave mirror:
Object position: Near mirror (inside focal point)
Image position: on the opposite side of the mirror as the object
Type of image: Virtual
Orientation of image: Same as object
Size of Image: Magnified
-Concave mirror:
Object position: Far from mirror (outside focal point)
Image position: same side of the mirror as the object
Type of image: real
Orientation of image: opposite of object
Size of Image: diminished
-Convex mirror:
Object position: Anywhere
Image position: on the opposite side of the mirror as the object
Type of image: Virtual
Orientation of image: Same as object
Size of Image: diminished
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