CH 1- Light Flashcards
Laws of reflection of light
Law 1: the incident Ray, the normal at the point of incidence and the reflected Ray all lie on the same plane
Law 2: the angle of incidence is equal to the angle of reflection (i=r)
Virtual image
Image formed by the apparent intersection of Ray’s
Is the same distance behind mirror as object in front
On perpendicular from object to mirror
Parallax
The apparent movement of one object relative to another to to the motion of the observer
Object farthest appears to move
Reflection
The bouncing of light off an object
When objects are in a state of no parallax they must be
In the same line and the same distance from the observer
Use this to locate image of object in plane mirror
Real image
Image formed by the actual intersection of Rays
Can be located by screen or method of no parallax
For a concave mirror
If image is outside focus it is real and located in front of the mirror
If real: 1/u + 1/v = 1/f
If image is inside or at focus it is virtual and behind mirror
If virtual: 1/u - 1/v = 1/f
MAGNIFICATION
Note:when finding m, v is always positive as distance is always positive
Magnification =
height of image Image distance
—————- = —————
height of object Object distance
Magnification= v/u
For a convex mirror
Image is always virtual and located behind mirror
Image is always diminished- the nearer to the mirror the object is the bigger the image
1/u - 1/v = - 1/f
Refraction
The bending of light as it passes from one medium to another
1) when light travels from a rarer to a denser medium it is refracted ______
2) when light travels for a denser to a rare medium it is refracted _____
1) towards the normal
2) away from the normal
Laws of refraction of light
Law 1 and snell’s law
Law 1) the incident Ray, the normal at the point of incidence and the refracted Ray all lie on the same plane
Law 2) the ration of the sine of the angle of incidence to the sine of the angle of refraction is a constant, n
n is the refractive index between two media
Refractive index of a medium
The ratio of the sine of the angle of incidence to the sine of the angle of refraction when light travels from a vacuum into that medium
For any two media x and y
xNy = 1 / yNx
aNg = sin i
—–
Sin r
gNa = sin r
—–
Sin i
Refractive index of a medium
Apparent depth
Of object
( when viewed from air with perpendicular line of view)
If the speed in medium one is c1 and the speed in medium two is c2 it follows that ___
1n2 = C1
—
C2
ie:
C1. Sin i
— = —–
C2. Sin r
It follows that refractive index of a medium= speed of light in air over speed of light in medium
Critical angle
When light travels from a denser to a rare medium the angle of incidence whose corresponding angle of refraction is 90 degrees is Called the critical angle (C) for those two media
Total internal reflection
When light going from a denser to a rarer medium strikes the second medium with an angle of incidence greater than the critical angle, it is reflected back into the denser medium, this is called TIR
Refractive index of a medium
SinC
Optical fibre
A very thin transparent rod through which light can travel by total internal reflection
Transmission of light through optical fibre
Light enters fibre and strikes inside at angle greater than critical angle
Ray is reflected to opposite side and TIR occurs again
This process continues and light travels
Dangers:
If fibre is bent through too large an angle light can escape
Light can escape when it comes into contact with another fibre or itself
How to overcome flaws of fibre optics
Coat fibres in material of lower refractive index
Uses and advantages of optical fibres
Telephones- light pulses
Energy losses in optical fibres are smaller than losses in electrical cables
Optical fibres smaller than electrical
Much less interference
Mirages
Refractive index of air changes with temperature
This causes mirages
Road absorbs heat and heats air above it
Hot air is thinner than cold and has lower refractive index
Light swerves
Goes down and up
