Modul PBD (Guru)

Explain the suitability of each features of the optical fibre in Table 11 for the use
in medicals. Determine the most suitable optical fibre. Give reason for your
choice.

Characteristics Reason
The refractive index of inner core is Easy for light ray to experience the
higher than the cladding core total internal reflection
Longer length of optical fibre Can enter deep inside the internal part
of patient
Smaller diameter of optical fibre Can enter the narrow path
High flexibility of fibre Can be bent easily

So, optical fibre R is chosen because it has higher refractive index of inner core
compared to outer cladding, has long with smaller diameter of fibre and the
flexibility of fibre is high.

12 Diagram 12 shows a crew of a submarine looking through a mirror periscope. The PL4
ship look small and blur in view.

Diagram 8
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You are required to suggest suitable modifications to make the image of the object

become sharper and bigger.

State and explain your suggestions based on the characteristic of material for the

body and additional feature for the periscope.

Characteristics Reason

Stainless steel body - durable

- rust proof

Use of prisms - to let the total internal

reflection occur so as to

produce sharper image

Use of convex lens - to magnify the image

The objective lens with bigger - to allow more light to enter

diameter the lens

- clearer image

The inner part is paint black - to avoid double reflection

colour - to absorb light that reach the

wall of the periscope

13 Presbyopia is an inability of the eye to adjust the focussing of far and near objects.
This usually happens when we get old, where the ciliary muscles is less able to
change the shape of the eye lens to focus the image on the retina, as shown in
Diagrams 13.1 and 13.2.

Diagram 13.1 Diagram 13.2

As an optician, you have three designs of lenses, X, Y and Z, in your shop. The
cross-section of X, Y and Z are shown in Diagram 13.3.

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Diagram 13.3
(a) Choose the most suitable design of lens in Diagram 13.3 to correct the sight PL5

of a person with presbyopia and explain the suitability of the design.
Design Y is the most suitable. This design contains the diverging and
converging lens.
- The diverging lens is used to focus the image from a faraway object

onto the retina.
- The converging lens is used to focus the image from a near object onto

the retina.

(b) Explain why the other two designs are not suitable.
Design X :
the image of the faraway object does not fall onto the retina so the faraway
object cannot be seen.
Design Z :
the image of a near object does not fall onto the retina so near object cannot
be seen.

14 (a) What do you understand about critical angle ? LP1
Incident angle when refracted angle is 90°

(b) Complete the sentence below using your own word. LP1

As light travel from high density to low density medium, the light refracted
away from normal.

15 State two condition that can make total internal reflection happen. LP2
i) Light travel from high density medium to low density medium
ii) Angle of incident is greater than critical angle

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16 Diagram 16 shows a laser beam trapped in a spurts of water. LP3

Diagram 16

(a) Explain why does the beam can be trapped in the water spurt. LP4

When water travel along the water spurt, it travels from high density medium

to low density medium. Laser beam makes an angle that is greater than the

critical angle. Light totally reflected back into the medium.

(b) If the refractive index of water is 1.33, what is the minimum angle of the
beam should be pointed at so that all the beam are totally reflected into the
water?
refractive index = 1.33
1 = 1.33

sin

sin c = 1

1.33

sin c = 0.75
c = sin-1 0.75
= 48.59⁰

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