Chapter 10: Light Flashcards
Types of light rays
Parallel
Convergent
Divergent
First law of reflection
The first law of reflection states that the incident ray, reflected ray and the normal at the point of incidence all lie in the same plane
Second law of reflection
The second law of reflection states that the angle of incidence is equal to the angle of reflection (i = r)
Reflection
The rebounding of light at a surface
Incident ray
Light ray that hits the reflecting surface
Point of incidence
The point at which the incident ray hits the reflecting surface
Normal
The perpendicular to the reflecting surface at the point of incidence
Reflected ray
Light ray that bounces off the reflecting surface
Angle of incidence
The angle between the incident ray and the normal
Angle of reflection
The angle between the reflected ray and the normal
Types of reflection
Regular
Diffuse (irregular)
Characteristics of regular reflection
Occurs at smooth surfaces eg mirrors
The law of reflection holds true for each individual ray: angle of incidence = angle of reflection
Parallel incident rays are reflected in the same direction as the surface is smooth. All rays have the same angles of incidence and reflection
The normal at all points of incidence are parallel to one another
Characteristics of diffuse reflection
Occurs at rough surfaces eg cloth
The law of reflection holds true for each individual ray: angle of incidence = angle of reflection
Parallel incident rays are reflected in different directions because the surface is uneven. The angles of incidence and reflection of one ray are different from those of another ray
The normal at all points of incidence are not parallel to one another
Characteristics of a plane mirror image
The image is of the same size as the object
Laterally inverted
Upright
Virtual
Its distance from the mirror is equal to the distance of the object from the mirror
Applications of mirrors
Vision testing
Blind corner mirror
Periscope
Refracted ray
Light ray that enters a medium and undergoes a change of direction
Refraction
The bending of light as light passes from one optical medium to another
First law of refraction
The first law of refraction states that the incident ray, refracted ray and the normal all lie in the same plane
Second law of refraction (Snell’s Law)
The second law of refraction states that, for two given media, the ratio of the sine to the angle of incidence to the sine of the angle of refraction is a constant
sin i / sin r = constant
Refractive index of a medium
The ratio of the speed of light in vacuum to the speed of light in the medium
n = c / v
n = sin i / sin r
Critical angle
The angle of incidence in an optically denser medium for which the angle of refraction in the optically less dense medium is 90 degrees
Total internal reflection
the complete reflection of a light ray inside an optically denser medium at its boundary with an optically less dense medium
conditions:
1. the light ray in an optically denser medium strikes its boundary with an optically less dense medium
2. the angle of incidence is greater than the critical angle of the optically denser medium
applications:
binoculars
periscopes
single lens reflex (SLR) cameras
Focal length
the distance between the optical centre and the focal point
