FUNPHYS 22 - Refraction, Fibre-optics and Endoscopy Flashcards
Define Refractive Index (n).
The Refractive Index (N) of a medium is defined as the ratio of the speed of light in a vacuum (C) to the speed of light in the medium (V).
- C = 3 x 10^8 m/s
- Refractive Index >= 1
- Refractive Index is similar to acoustical impedance in sound
When does refraction occur?
Refraction occurs when light travels from one medium to another medium with a different refraction index.
What is Snell’s Law?
Snells’s Law is the relationship between the angle of incidence and the angle of refraction. There are two cases:
- When light travels from a LESS dense medium to a MORE dense medium, the refracted angle bends TOWARDS the normal.
- When light travels from a MORE dense medium to a LESS dense medium, the refracted angle bends AWAY from the normal.
What happens ONLY when light travels from a more dense medium to a less dense medium, and what happens to each type of light?
When light travels a more dense medium to a less dense medium some light is refracted and some light is reflected. As the angle of refraction increases (moves away from the normal), the angle of refraction intensity decreases, and the angle of reflection intensity increases.
What is a critical angle?
The angle of incidence becomes a critical angle when the refracted angle is equal to 90 degrees and lies parallel to the surface. This is when Total Internal Reflection begins
What is Total Internal Reflection?
Total Internal Reflection is when the incident angle is greater than the critical angle, causing all light to be reflected and none to be refracted. No light intensity is lost between the incident beam and the reflected beam during Total Internal Reflection.
Why does TIR only occur from when light travels from a more dense medium to a less dense medium?
TIR only occurs when a light travels from a more dense medium to a less dense medium because reflection only occurs when light travels from a more dense medium to a less dense medium.
How does a fiber-optic cable work?
Fiber-optical cables use the concept of TIR to pass a ray of light through the cable. The consists of a core surrounded by cladding that has a higher Refractive Index than the core, to allow reflection to occur. As long as the ray of light exceeds the critical angle for the fiber, TIR will occur and light intensity will not diminish throughout the entire cable. Single fiber optic cables cannot transmit multiple images because multiple reflections within the cable will cause the object to be scrambled.
What is Numerical Aperture? (N.A.)
It is a measure of the amount of light that can be collected by an optical system. It is dependent on the Acceptance angle. The larger the acceptance cone, the higher the Numerical Aperture. The smaller the acceptance cone, the smaller the Numerical Aperture.
What is endoscopy?
Endoscopy is the examination and inspection of the interior of body organs, joints, or cavities through an endoscope to allow physicians to see through the body’s passageways. There are two types:
- flexible endoscopy
- surgical endoscopy
What are the different types of flexible endoscopy?
- Laryngoscopy (larynx)
- Gastroscopy (oesophagus -> small intestine)
- Colonoscopy (colon)
- Proctoscopy (anus & rectum)
- Bronchoscopy (lungs)
- Thoracoscopy (chest cavity)
- Cystoscopy (bladder)
What are the different types of surgical endoscopy?
- Laparoscopy (incision in the abdomen)
- Arthroscopy (incision in the skin near a joint)
- Nasopharyngoscopy (nose)
- Proctoscopy: (rectum)
What is capsule endoscopy?
A disposable flash camera, that resembles a vitamin pill, that is digested by a patient. The minicamera takes pictures in the small intestine and the images are transmitted to a recorder that the patient wears around their waist. After 8hrs the capsule runs out of battery and is eliminated through the faeces. Then the recorder’s images are downloaded to a computer to be viewed.
What is an endoscope?
An endoscope consists of two bundles of fiber-optic cables - illuminating fibers (requires large diameter cables) and viewing fibers (requires smaller diameter cables), a biopsy channel, and an air/water channel. Together they provide light and visualization of the interior of a joint or cavity. The quality and resolution of the image are dependent on the diameter and the quantity of each fiber-optic cable.
