Chapter 1: Imaging

Question 1

What is the Wave Equation?

Answer 1

v = fλ

Question 2

How can images be recorded electronically?

Answer 2

With microsensors, such as charge-coupled devices (ccd)

Question 3

How can images be recorded on an atomic scale?

Answer 3

By scanning methods; such as an atomic force microscope (AFM) or a scanning tunnelling microscope (SEM and TEM)

Question 4

How are images stored digitally?

Answer 4

As an array of pixels, each of which is defined by a number.

Question 5

How can images be smoothed?

Answer 5

By different types of averaging techniques. They can also be sharpened with edge detection.

Question 6

What is the lens equation?

Answer 6

1/v=1/f+1/v

Question 7

What does the Cartesian convention state?

Answer 7

You should measure from the lens to the right as positive and from the lens to the left as negative. Therefore, u is always negative whilst v is positive.

Question 8

When does refraction occur?

Answer 8

When a wave changes speed by moving from one medium into another.

Question 9

What makes a material optically denser than another?

Answer 9

It slows down light more than another material.

Question 10

What is the purpose of a lens?

Answer 10

Lenses add curvature to wavefronts

Question 11

What is the focal length equal to for parallel incoming rays of light?

Answer 11

The image distance

Question 12

What is the lens power equation?

Answer 12

P = 1/f

Question 13

What are the units of optical power?

Answer 13

Dioptres (D)

Question 14

What is curvature defined as?

Answer 14

1/radius of curvature

Question 15

What is the equation for magnification?

Answer 15

m = size of image / size of object;

m=v/u

Question 16

What is the focal length of a lens?

Answer 16

The distance between the lens axis and the focus.

Question 17

What happens to a wave as it passes through a thin converging (convex) lens?

Answer 17

The rays of light will converge to the focal point.

Question 18

What is a bit?

Answer 18

A single digit (0 or 1)

Question 19

What is a byte?

Answer 19

8 bits

Question 20

Number of bits =

Answer 20

amount of information

Question 21

Equation for number of possible alternatives, N

Answer 21

N = 2^I
or
log_2(N)=I

Question 22

What is an image?

Answer 22

An array of pixels each needing an 8, 16 or 24 bit colour code.

Question 23

How many possible alternatives does 8 pixels give?

Answer 23

N = 2^I = 2^8 = 256

Question 24

What is a CCD?

Answer 24

Array of tiny sensors mounted on a chip, detecting light levels. Information from each sensor is recorded and converted to a pixel value.

Question 25

How do you reduce the noise in an image?

Answer 25

You replace the value of a pixel by the median value of the pixel and its eight neighbouring pixels.

Question 26

How do we detect edges?

Answer 26

Using the Laplace rule: multiply a pixel’s value by 4 and then subtract the values of the pixels to the pixel’s north, south east and west from it.

Question 27

Types of image

Answer 27

ultrasound, visible light, radar, IR, X-rays, electron scattering…

Question 28

What is RESOLUTION?

Answer 28

The smallest object or distance distinguishable.,

Question 29

What is the equation for the displacement at any one point in a wave?

Answer 29

s = A sin(2πft - ϕ)

Question 30

Name an application of gamma rays

Answer 30

Sterilisation of medical instruments; medical imaging

Question 31

Name an application of X rays

Answer 31

medical imaging

Question 32

Name an application of UV light

Answer 32

sun beds/security markers

Question 33

Name an application of visible light

Answer 33

photography, seeing

Question 34

Name an application of IR radiation

Answer 34

fibre optic communication

Question 35

Name an application of microwaves

Answer 35

cooking food; satellite communications

Question 36

Name an application of radio waves

Answer 36

broadcasting and communication

Question 37

Name a typical source of gamma rays

Answer 37

Decay of a radioactive nucleus

Question 38

Name a typical source of X rays

Answer 38

Inner shell atomic electron transitions

Question 39

Name a typical source of UV rays

Answer 39

Atomic electron transitions

Question 40

Name a typical source of visible light

Answer 40

Outer shell atomic electron transitions

Question 41

Name a typical source of infrared rays

Answer 41

vibrations of atoms and molecules

Question 42

Name a typical source of microwaves

Answer 42

electrons in resonant cavities

Question 43

Name a typical source of radio waves

Answer 43

electrons oscillating/accelerating and decelerating in an aerial.