2.2 Refraction Flashcards
What is refraction
Bending of light as it passes between materials of different refractive indexes
Why does light refract
Speed change
2 conditions necessary for refraction
Angle of incidence > 0degrees
Light has to travel between media with different refractive indexes
Speed of light in a vacuum
3x10^8
Everyday examples of refraction
Eyes
glasses
Fibre optic cables
Snells law
At a boundary between 2 media the ratio of the sine of the angle of incidence to the sine of refraction is constant
Critical angle definition
Angle of i that gives angle of r to be 90
2 conditions for total internal reflection
Ray must be incident from a medium with a higher refractive index to a lower refractive index
Angle i must be bigger than the critical angle
Describe the structure and components of an endoscope
Contains bundles of optical fibres, 1 for illumination and another for observation.
Illuminating bundle is non-coherent.
Fibres in bundle providing image is coherent/has the same spatial relationship.
Coherent bundle is attached to eyepiece.
Tubes for irrigation.
Control cables allow for change of view.
Experiment for verifying Snell’s law
Place glass block on sheet of paper and trace around it
Mark the normal on the glass block
Add the ray box so the light is travelling through the block at an angle > 0 to the normal
Mark with 2 crosses the point which the light enters and leaves the glass block
Draw the rays in showing a ray entering block, in the block and leaving the block
Measure the angles of i and r
Repeat the experiment with multiple different angles of i
Describe a Step index optical fibre (3)
Light is sent through fibre from one end to another
Refraction at the entrance
This involves total internal reflection of light at the cladding-core boundary
Equation for critical angle
sin c = 1/n
Equation for refractive index
n = sin i /sin r
Equation for n involving speed of light c
n = c1 / c2
Define magnification
Ratio of image height to object height
