Unit 3 Flashcards
Define: CT scan
Stands for Computerised Tomography. Gives a 360o scan of the body. Can distinguish between soft tissues.
Define: X-rays
Part of the electromagnetic spectrum with a very short wavelength. They cause ionisation.
Define: Mutation
A change to the DNA of a living thing.
Define: Charge-Coupled Device
Allows formation of electronic images when using X-rays
Define: Ultrasound
Sounds above 20,000Hz i.e. above the range of human hearing
Define: Media
Different materials with differing properties
Define: Refraction
Change of direction of light as it passes from one medium to another
Define: Lens
Forms an image by refracting light. Often made of glass.
Define: Converging lens
Parallel rays of light are brought to a focal point (the principal focus). Also known as a convex lens. Has positive power.
Define: Diverging lens
Forms a virtual image on the same side as the original image. Has negative power.
Define: Focal length
Distance from the lens to the principal focus
Define: Refractive index
Measure of how greatly a substance slows the velocity of light
Define: Snell’s Law
Refractive index = sin i ÷ sin r
Define: Virtual image
Where the light rays appear to have come from. An image which doesn’t form on a screen, but can be seen with an eye or captured by a camera. Formed where virtual rays converge.
Define: Real image
Formed at the point where the light rays converge (cross). Can be put on a screen.
Define: Ray diagram
Diagram showing the image that will form with a particular lens and an object in a particular location
Define: Retina
The light sensitive cells around the inside of the eye
Define: Lens
Focuses light onto the retina
Define: Cornea
A transparent layer that protects the eye and helps focus light onto the retina
Define: Iris
Coloured ring of muscle that controls the amount of light entering the eye
Define: Pupil
The central hole formed by the iris. Light enters the eye through the pupil
Define: Ciliary muscle
Attached to the lens by suspensory ligaments. The muscles change the thickness of the eye lens
Define: Suspensory ligaments
Hold the lens in place
Define: Vitreous humour
Transparent jelly-like substance that supports the back of the eye
Define: Aqueous humour
Transparent watery liquid that supports the front of the eye
Define: Blind spot
Region where the retina is not sensitive to light because no light sensitive cells are present.
Define: Optic nerve
Carries nerve impulses from the retina to the brain.
Define: Eye muscles
Move the eye in the socket
Define: Long sight
Where the eyeball is too short or the lens is unable to focus. Corrected with a converging lens
Define: Short sight
Where the eyeball is too long or the lens is unable to focus. Corrected with a diverging lens
Define: Range of vision
25cm - infinity
Define: Near point
Closest the eye can focus (25cm)
Define: Far point
Furthest the eye can focus (infinity)
Define: Total internal reflection
Occurs when the angle of incidence of a light ray in a transparent substance is greater than the critical angle
Define: Critical angle
The angle of incidence of a light ray in a transparent substance that produces refraction along the boundary
Define: Refractive Index
1/sin c where c is the critical angle
Define: Endoscope
An optical fibre that uses total internal reflection to allow transmission of light
Define: Lasers
Used as an energy source for cutting, cauterising and burning
