Unit 3

Question 0

Define: CT scan

Answer 0

Stands for Computerised Tomography. Gives a 360o scan of the body. Can distinguish between soft tissues.

Question 1

Define: X-rays

Answer 1

Part of the electromagnetic spectrum with a very short wavelength. They cause ionisation.

Question 2

Define: Mutation

Answer 2

A change to the DNA of a living thing.

Question 3

Define: Charge-Coupled Device

Answer 3

Allows formation of electronic images when using X-rays

Question 4

Define: Ultrasound

Answer 4

Sounds above 20,000Hz i.e. above the range of human hearing

Question 5

Define: Media

Answer 5

Different materials with differing properties

Question 6

Define: Refraction

Answer 6

Change of direction of light as it passes from one medium to another

Question 7

Define: Lens

Answer 7

Forms an image by refracting light. Often made of glass.

Question 8

Define: Converging lens

Answer 8

Parallel rays of light are brought to a focal point (the principal focus). Also known as a convex lens. Has positive power.

Question 9

Define: Diverging lens

Answer 9

Forms a virtual image on the same side as the original image. Has negative power.

Question 10

Define: Focal length

Answer 10

Distance from the lens to the principal focus

Question 11

Define: Refractive index

Answer 11

Measure of how greatly a substance slows the velocity of light

Question 12

Define: Snell’s Law

Answer 12

Refractive index = sin i ÷ sin r

Question 13

Define: Virtual image

Answer 13

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.

Question 14

Define: Real image

Answer 14

Formed at the point where the light rays converge (cross). Can be put on a screen.

Question 15

Define: Ray diagram

Answer 15

Diagram showing the image that will form with a particular lens and an object in a particular location

Question 16

Define: Retina

Answer 16

The light sensitive cells around the inside of the eye

Question 17

Define: Lens

Answer 17

Focuses light onto the retina

Question 18

Define: Cornea

Answer 18

A transparent layer that protects the eye and helps focus light onto the retina

Question 19

Define: Iris

Answer 19

Coloured ring of muscle that controls the amount of light entering the eye

Question 20

Define: Pupil

Answer 20

The central hole formed by the iris. Light enters the eye through the pupil

Question 21

Define: Ciliary muscle

Answer 21

Attached to the lens by suspensory ligaments. The muscles change the thickness of the eye lens

Question 22

Define: Suspensory ligaments

Answer 22

Hold the lens in place

Question 23

Define: Vitreous humour

Answer 23

Transparent jelly-like substance that supports the back of the eye

Question 24

Define: Aqueous humour

Answer 24

Transparent watery liquid that supports the front of the eye

Question 25

Define: Blind spot

Answer 25

Region where the retina is not sensitive to light because no light sensitive cells are present.

Question 26

Define: Optic nerve

Answer 26

Carries nerve impulses from the retina to the brain.

Question 27

Define: Eye muscles

Answer 27

Move the eye in the socket

Question 28

Define: Long sight

Answer 28

Where the eyeball is too short or the lens is unable to focus. Corrected with a converging lens

Question 29

Define: Short sight

Answer 29

Where the eyeball is too long or the lens is unable to focus. Corrected with a diverging lens

Question 30

Define: Range of vision

Answer 30

25cm - infinity

Question 31

Define: Near point

Answer 31

Closest the eye can focus (25cm)

Question 32

Define: Far point

Answer 32

Furthest the eye can focus (infinity)

Question 33

Define: Total internal reflection

Answer 33

Occurs when the angle of incidence of a light ray in a transparent substance is greater than the critical angle

Question 34

Define: Critical angle

Answer 34

The angle of incidence of a light ray in a transparent substance that produces refraction along the boundary

Question 35

Define: Refractive Index

Answer 35

1/sin c where c is the critical angle

Question 36

Define: Endoscope

Answer 36

An optical fibre that uses total internal reflection to allow transmission of light

Question 37

Define: Lasers

Answer 37

Used as an energy source for cutting, cauterising and burning