Physics: Structured Paper P3 - Topic 6

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Total Internal Reflection

Refraction is caused by the waves changing speed and direction and going into a different medium eg. solid to gas.

When waves SLOW DOWN they bend towards the NORMAL

When LIGHT enters the GLASS or PLASTIC it SLOWS DOWN

If a wave HITS a BOUNDARY at 90degrees, it will NOT change direction.

When the light hits a DIFFERENT MEDIUM some of the light will PASS THROUGH the new medium & some REFLECTED.

IT ALL DEPENDS ON THE ANGLE ON INCIDENCE (ANGLE IT HITS) 

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Total Internal Reflection Diagram

(http://www.fiberoptics4sale.com/Merchant2/fofs_img/total-internal-reflection.gif)

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Medical Uses of Light

ENDOSCOPES use bundles of OPTICAL FIBRES.
To look inside the body without risk of scars and blood loss. (KEYHOLE SURGERY) 

Pulse Oximeters use light to check the % of oxygen in the blood!!
Used for monitoring someones health before & after surgery. 

You put the pulse oximeter on your finger- 
The amount of light absorption depends on the bloods colour and oxyhaemoglobin content.

The oximeter emits red and infared light into someones finger or ear with a detector underneath. 

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