P3.1 Lenses and the eye

Question 1

What is refraction?

Answer 1

• The CHANGE OF DIRECTION of light

- as it passes from one medium to another

Question 2

How does a lens form a image?

Answer 2

By refracting light

Question 3

What shape is a convex or converging lens?

Answer 3

()

Question 4

Where is the principal focus?

Answer 4

• In a converging lens

- where are PARALLEL rays of light are brought to a FOCUS

Question 5

What is the focal length?

Answer 5

Distance from the lens to the principal focus

Question 6

What are the six words used to describe an image?

Answer 6

Magnified/Diminished
Upright/Inverted
Real/Virtual

Question 7

In what situation do light rays bend towards the normal?

Answer 7

When light passes from a LOWER density substance TO a HIGHER density

Question 8

What kind of lens is used for a magnifying glass?

Answer 8

Converging

Question 9

What are the 6 features of an eye?

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Answer 9

Retina, Lens, Cornea, Pupil /iris, Ciliary muscle, Suspensory ligaments.

Question 10

What are the functions of the iris and the pupil?

Answer 10

Iris= CONTROLS how much LIGHT enters pupil

Pupil=Allows light through

Question 11

What are the functions of the suspensory ligaments and cillary muscle?

Answer 11

Suspensory= CONNECTS cillary to lens. HOLDS lens. Slacken or stretch as cillary contract
Cillary= ADJUSTS LENS shape

Question 12

What does adjusting the lens shape do to light?

Answer 12

Increases or decreases the refraction of light

Question 13

What are the functions of the cornea and the lens?

Answer 13

Cornea= REFRACTS light as it enters the eye
Lens= REFRACTS light to focus it into the retina

Question 14

What is the function of the retina?

Answer 14

Contains light receptors which trigger electrical impulses to be sent to brain when light’s detected

Question 15

An object is near. Describe the (a) cillary… (b) suspensory… (c) muscle tension on lens (d) lens shape

Answer 15

(a) contracted
(b) slackened
(c) low
(d) fat, more curved

Question 16

What is long and short sight?

Answer 16

LONG= eyeball too SHORT, lens can't focus
SHORT= eyeball too LONG, lens can't focus

Question 17

What is the power of converging lens? Positive or negative?

Answer 17

CONVERGING=POSITIVE

Question 18

Compare the human eye to a camera. Make 3 points

Answer 18

-Both use converging lens
-Inverted image
IRIS= APERTURE
FILM/CCD= RETINA
FOCUSING SCREW= CILLARY MUSCLES

Question 19

What is the focal length of a lens determined by?

Answer 19

Refractive index of lens material

Curvature of the two surfaces of the lens

Question 20

The greater the focal length…

What does this mean for manufacturing?

Answer 20

…the flatter the lens.

The lens can be manufactured thinner

Question 21

What is the concept of the critical angle?

Answer 21

When, beyond a certain (CRITICAL) angle, all the waves reflect back into the glass.

Question 22

What is the phrase for all of the waves reflecting back into the glass?

Answer 22

TOTAL INTERNAL REFLECTION

Question 23

What can optical fibres carry (not in the body)?

Answer 23

Visible light

Question 24

What does a laser do and what is it used for?

Answer 24

• Cuts, Burns, Cauterises

- Cutting things, laser eye surgery

Question 25

What else can optical fibres be used for?

Answer 25

ENDOSCOPES to carry light, for doctor to SEE (e.g. keyhole) and DIAGNOSE (e.g. cancer)