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Myopia (Near-sightdness)
Nearsightedness is treated with a diverging lens, which makes up for the eye's over-convergence. The diverging lens produces the image closer to the eye than the object, allowing the nearsighted individual to clearly see it.
Comparison of Normal Vision (Left) and Myopia Vision (Right)
Light is brought to a focus in front of the retina
Distance between retina and lens is too large or the cornea-lens combination converges light to strongly
When an individual has difficulty seeing objects that are far away
Hyperopia (far Sightdness)
How do people correct this vision? What lens is used?
A converging lens is used to correct farsightedness by compensating for the eye's under convergence. The converging lens creates an image that is farther away from the eye than the object, allowing the farsighted individual to clearly see it.
Comparison of Normal Vision (Left) and Hyperopia Vision (Right)
Causes light from all nearby objects to focus behind the retina
Distance between the retina and the eye shape is too small and/or cornea lens combination is too weak
When an individual has difficulty seeing nearby objects
In a camera, the image is focused on FILM or on a DIGITAL SENSOR. The RETINA at the back of each eye cavity performs the same function as light-sensitive cells. The retina transforms light into an electrical signal that the optic nerve sends to the brain.
A camera has a CONVERGING LENS to refract light to form a sharp image. The eye also has structures, the LENS and CORNEA, that cause light to converge. The cornea is the transparent bulge on top of the pupil that focuses light. Light is refracted more through the cornea than through the lens.
The PUPIL compares to the APERTURE on a camera. This the opening in the iris through which light reaches the eye.
A camera has a DIAPHRAGM that controls the amount of light entering it. The coloured part of the eye, also known as the “IRIS” has this function as it opens and closes around a central hole to let in more or less light.
Image with all the parts of the structure of eye
Lens
Optic Nerve
Cornea
Iris
Pupil
Retina
Image above states what we find out with this equation
Image above states what we find out with this equation
Cases
Only Case- Object is at any location
NOTE: 2F and 2F' are always TWICE the distance of f and f' respectively
3) A ray through the optical center (0) passes straight through without being refracted
2) A ray that appears to pass through the secondary principal focus (F) is refracted parallel to the principal axis
1) A ray parallel to the principal axis is refracted as if it had come through the principal focus (F)
Case 5 - Object inside F
Case 4 - Object at F
Case 3 - Object is between F and 2F
Case 2 - Object is at 2F'
Case 1- Object is beyond 2F'
Rules/Steps
3) A ray through the optical center (O) passes straight through without being refracted
2) A ray through the secondary principal focus (F') is refracted parallel to the principal axis
1) A ray parallel to the principal axis is refracted through the principal focus (F)
Principal Focus "F"
F' - Secondary Principal Focus
F-Primary principal focus
Diverging Lens: Same side of the lens as the incident ray
Converging lens: opposite side of the lens as incident ray
Optical Center: The exact center of the lens "O"
F and F' are equal to length in 'O"
Principal Axis "PA": A line that passes through the center of the lens normal to the lens surfaces
ni (sin˚i) = nR (sin˚R) or n1 (sin˚1) = n2 (sin˚2)
ni=index of refraction for medium 1 nR= index of refraction for medium 2
Key Ideas of Total Internal Reflection -Only occurs when light travels from slow to fast medium -Occurs when angle of incidence is greater than the critical angle
The Critical Angle is the angle of incidence that results in an angle of refraction of 90°
Air has a index of refraction of 1.0003
***NOTE :
Angle of Refraction - Capital R -
Angle of incidence does not equal angle of Refraction
Examples of Convex Mirrors in our Everyday lives
Convex mirrors are used in convenience stores as convex mirrors have a wider field of view and can cover a larger area with a single mirror. This makes it easier to monitor the store
Case
Only Case
Rules/steps
3) A ray aimed at F is reflected parallel to the principal axis Green line on image below
2) A ray aimed at C is reflected back upon itself - Blue line on image below
1) A parallel ray that extends from the top of the object to the mirror and is reflected back to the viewer (virtual extension to focal point behind the mirror) - Red Line on image below
gets smaller in size than the object, but as the object approaches the mirror, it grows larger (maximum up to the size of the object).
Image is virtual
Concave mirrors in our Everyday lives
A Dentist uses concave mirrors to get a magnified effect to see your teeth. Therefore, the image is larger making it easier for the dentist to see
Cases for Concave Mirrors
Case 5 - Object is between F and mirror
Case 4 - Object is at F
Case 3 - Object is between C and F
Case 2 - Object is at C
Case 1 - Object is beyond C
Rules/steps for Concave mirrors
5) Where two reflected rays intersect is where the image will form
4) A ray aimed at the V obeys the laws of reflection (
3) 2nd incident ray passing through the F is reflected, parallel to the PA
2) A ray passing through the C is reflected back onto itself
1) 1st incident ray parallel to the PA is reflected through the F
Characteristics
- Can produce real and virtual images, image can enlarged, smaller, or the same size
Focal Length "f" Distance between F and V
Focal Point "F" Halfway point between C and V
Distance between C and V is the radius
Vertex "V" The point where the principal axis meets the mirror
Principle Axis "PA" The line that passes through the centre of curvature (C) to the midpoint of the mirror
Center of Curvature "C" The centre of the sphere whose surface has been used to make the mirror and all "Normals" meet at C
An image of a ray diagram with all the steps listed above
6) Repeat for each point on the object. Connect the points of the image using a dashed line
5) Using dashed lines, extend both reflected rays behind the mirror until they meet. Label this point
4) Measure the angle of incidence with a protractor. Apply the law of reflection and draw the reflect ray
3) Draw Another incident ray striking the mirror (at an angle) At that point it hits the mirror, draw a normal
2) Draw at least two incident rays (from each point on the object) and draw the reflected ray directly towards the mirror at 90 degrees
1) Draw at least two incident rays (from each point on the object)
Image that corresponds with descriptions of solide and dashed lines
Image shows where the angle of incidence and reflection is and the normal
The behavior of light: Light travels in straight lines and when emitted from a source to strike an object, it creates an incident light
When we see objects, we are actually seeing light being reflected
An example: X-rays are plaed on the placed on the right side of the spectrum as they have high frequency and more energy
An example: Radio waves are placed on the left side of the spectrum as they have low frequency and less energy
