Optics Flashcards
Diffuse reflection
Light is scattered in all directions due to the rough surface
Regular reflection
Light is reflected off as it’s shown due to a smooth surface eg. Plane mirror
Laws of reflection
The incident Ray, the normal at the point of incidence & the reflected Ray all lie on the same plane
Angle of incidence =angle of reflection
Virtual image
Formed by the apparent intersection of Rays
Real image
Formed by the actual intersection of light rays
Lateral inversion
the apparent reversal of the mirror image’s left and right when compared with the object.
Mirror parallax
Apparent movement of one object relative to another due to the motion of the observer
Furthest object seems to move
State of no parallax
In the same line
No distance between them
Can be used to locate an object in the mirror
Concave mirror
Caves in
Rules for drawing a ray diagram
Parallel & focal point
Focal point & parallel
Centre of curvature
Uses of concave mirrors
Searchlights, floodlights, headlights in a car, shaving mirrors
Convex mirror
Image is always diminished upright & virtual
Uses of convex mirrors
Door mirror of a car
In shops to deter shoplifters
At concealed entrance to give a view of oncoming traffic
Mirror formula
Real image 1/u + 1/v =1/f
Virtual image 1/u - 1/v =1/f
Magnification v/u
Reflection
The bouncing of light off an object
Precautions that should be taken when measuring the distance in the focal lenght of a concave mirror experiment
Measure from the back of the mirror/ measure from the centre of the mirror/ avoid parallax error/ensure image is sharp
How to find an approximate value for the focal lentgh
focus the image of a distinct object on the screen
Measure the distance between the mirror and the screen.
Refraction
the bending of a ray of light when it goes from one medium to another
Laws of Refraction
the incident ray, the normal at the point of incidence and the refracted ray all lie on the same plane
Snell’s Law: the ratio of the sin of the angle of incidence to the sin of the angle of refraction is a constant called the Refractive Index
Refractive Index
Sini/Sinr = n where n is a constant
Refractive Index of a medium
real depth/ apparent depth
Critical Angle (C)
when light travels from a denser to a rarer medium, the angle of incidence, whose corresponding angle of refraction is 90 degrees is called the critical angle
Critical Angle Formula
n = SinC/Sin90 = SinC/1 = SinC
Refractive index in terms of relative speeds
N = C1/C2 = Speed of air/ R.I of medium
Total Internal Reflection
If the angle of incidence in the denser of the two media is greater than the critical angle, the light is reflected back into the denser medium
Application of Total Internal Reflection
Reflective road signs, Optical Fibres, Endoscopes, Periscopes
Optical Fibre
Very thin transparent rod (usually glass) through which light can travel by total internal reflection
How Optical Fibres work
Light enters one end of the fibre & strikes the boundary between the two materials, at an angle greater than the critical angle, resulting in total internal reflection
How can light escape an optical fibre?
If it’s bent too much
If it comes into contact with another fibre
Uses of an Optical Fibre
Telecommunications and Endoscopes
Advantages of Optical Fibres over copper conductors
Less interference/ boosted less often/ cheaper raw material/ occupies less space/ doesn’t corrode
Experiment: to verify Snell’s Law and Hence measure the R.I of Glass - Sources of Error/ Precautions
Using small angles of incidence result in large percentage errors
Place two dots far apart on the incident and refracted light beam to accurately locate the beams
Convex Lens
If the image is outside the focus the image is real and inverted
If it’s inside the focus the image is virtual and upright
How light refracts in a convex lens
A ray strikes the optic centre, passes straight through the lens
A ray that travels parallel to the axis strikes the focus point on the other side of the lens
A ray which passes through the focus point and then strikes the lens, emerges parallel to the axis
Concave lens diagrams
From top of the object to the lens parallel to the principal axis and up as if coming from focal point.
From top of object to the lens as if passing through the centre of curvature
The power of then lens
1/ focal length
Unit is (m) -1
Equation: if two lenses are placed in contact the focal length f of the combination is
1/f= 1/f(1) + 1/f(2)
Power of Accommodation
The eyes ability to focus a real image of an object on the retina, whether the object is near of far away from the eye
Short sighted person
Can see nearby objects but cannot bring distance objects into focus
Long sighted person
Can see distant objects but cannot bring nearby objects into focus. It is corrected with a concave lens
