P3.1 Lenses and the eye Flashcards
What is refraction?
- The CHANGE OF DIRECTION of light
- as it passes from one medium to another
How does a lens form a image?
By refracting light
What shape is a convex or converging lens?
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Where is the principal focus?
- In a converging lens
- where are PARALLEL rays of light are brought to a FOCUS
What is the focal length?
Distance from the lens to the principal focus
What are the six words used to describe an image?
Magnified/Diminished
Upright/Inverted
Real/Virtual
In what situation do light rays bend towards the normal?
When light passes from a LOWER density substance TO a HIGHER density
What kind of lens is used for a magnifying glass?
Converging
What are the 6 features of an eye?
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Retina, Lens, Cornea, Pupil /iris, Ciliary muscle, Suspensory ligaments.
What are the functions of the iris and the pupil?
Iris= CONTROLS how much LIGHT enters pupil
Pupil=Allows light through
What are the functions of the suspensory ligaments and cillary muscle?
Suspensory= CONNECTS cillary to lens. HOLDS lens. Slacken or stretch as cillary contract Cillary= ADJUSTS LENS shape
What does adjusting the lens shape do to light?
Increases or decreases the refraction of light
What are the functions of the cornea and the lens?
Cornea= REFRACTS light as it enters the eye Lens= REFRACTS light to focus it into the retina
What is the function of the retina?
Contains light receptors which trigger electrical impulses to be sent to brain when light’s detected
An object is near. Describe the (a) cillary… (b) suspensory… (c) muscle tension on lens (d) lens shape
(a) contracted
(b) slackened
(c) low
(d) fat, more curved
What is long and short sight?
LONG= eyeball too SHORT, lens can't focus SHORT= eyeball too LONG, lens can't focus
What is the power of converging lens? Positive or negative?
CONVERGING=POSITIVE
Compare the human eye to a camera. Make 3 points
-Both use converging lens
-Inverted image
IRIS= APERTURE
FILM/CCD= RETINA
FOCUSING SCREW= CILLARY MUSCLES
What is the focal length of a lens determined by?
Refractive index of lens material
Curvature of the two surfaces of the lens
The greater the focal length…
What does this mean for manufacturing?
…the flatter the lens.
The lens can be manufactured thinner
What is the concept of the critical angle?
When, beyond a certain (CRITICAL) angle, all the waves reflect back into the glass.
What is the phrase for all of the waves reflecting back into the glass?
TOTAL INTERNAL REFLECTION
What can optical fibres carry (not in the body)?
Visible light
What does a laser do and what is it used for?
- Cuts, Burns, Cauterises
- Cutting things, laser eye surgery
What else can optical fibres be used for?
ENDOSCOPES to carry light, for doctor to SEE (e.g. keyhole) and DIAGNOSE (e.g. cancer)
