Structure of the Eye

• What type of lenses do our eyes contain?

  Converging lenses
• What does the refractive index affect in the eye?

  It causes different amounts of refraction
• Through which part of the eye do light rays enter?

  Cornea
• What is the function of the cornea?

  It covers the front of the eye
• What can variations in the cornea's shape lead to?

  Problems in focusing light on the retina
• What is the refractive index of the cornea compared to air?

  High refractive index
• What happens to the pupil in a dark room?

  The iris expands, dilating the pupil

  
• What occurs to the pupil in bright sunlight?

  The iris contracts, making the pupil smaller

  
• What liquid do light rays pass through after the cornea?

  Aqueous humour
• What is the near point for 'normal sighted' people?

  25 cm
• What is the far point for 'normal sighted' people?

  Infinity
• What do ciliary muscles control in the eye?

  The focal length of the lens

  
• What happens when ciliary muscles contract?

  The lens becomes wider and more powerful

  
• What is an unaccommodated lens?

  A thinner, less spherical lens
• What is the distance from the object to the lens denoted as?

  u
• What is the distance from the image to the lens denoted as?

  v
• What is the approximate distance from the lens to the fovea in an adult human?

  2 cm
• How should lens diagrams for the eye be drawn?

  Refracting once to show total refraction

  
• What does adding the powers of the cornea and lens give?

  Total power of the eye
• What happens when the ciliary muscles relax?

  The lens becomes thinner and less powerful

  
• What is the effect of a wider lens on focusing power?

  It has a stronger focusing power
• What is the effect of a narrower lens on focusing power?

  It has a smaller focusing power
• Where is light focused after passing through the lens?

  On the retina
• How is the image formed on the retina oriented?

  Upside down

  
• What does the brain do with the inverted image?

  Interprets it as correct way up
• What happens to rays from the top of an object?

  They focus on the bottom of the retina
• What are the light-sensitive cells in the retina called?

  Rods and cones
• What is the ratio of rods to cones in the retina?

  3:1

  
• How far away is the toy the boy is looking at?

  80 cm

  
• What is the diameter of the boy's eye from the lens to the fovea?

  1.75 cm

  
• What is the first step in completing the ray diagram?

  Sketch rays from the top of the toy

  
• What happens to the rays at the cornea?

  They are refracted towards the bottom of the image
• What is the second step in completing the ray diagram?

  Sketch rays from the bottom of the toy
• What is the first step in calculating the power of the boy's eye?

  Write known values in meters
• What is the lens equation used in the calculation?

  \( \frac{1}{f} = \frac{1}{u} + \frac{1}{v} \)
• What is the calculated value of \( \frac{1}{f} \) after substituting known quantities?

  58.4
• What is the formula for power in relation to focal length?

  P = \( \frac{1}{f} \)
• What is the power of the lens calculated for the boy's eye?

  58.4 D