Imaging

Question 1

What is curvature?

Answer 1

1/r
As r tends to infinity, curvature tends to 0. This means waves from a distant source have no curvature. They are called plane wave-fronts.

Question 2

Ways of modelling light

Answer 2

Ray point of view; arrows parallel to direction of travel.

Wave point of view; lines perpendicular to direction of travel.

Question 3

Lens power

Answer 3

Lens power (D) = 1/focal length (m)

Question 4

The Lens Equation

Answer 4

1/v = 1/u + 1/f (u is negative)
Curvature of waves leaving the lens equals the curvature of the waves entering the lens plus the curvature added by the lens.

Question 5

Position of image from varying sources

Answer 5

Very distant source = image at focus

Nearby source beyond focus = image passed the focus

Source at the focus = very distant image

Source inside the focus = virtual image

Question 6

Describing an image

Answer 6

Upright or inverted
Real or virtual
Magnified or diminished

Question 7

Image when the object is:

Greater than 2f away from lens
Between f and 2f
Within f of the lens

(with examples)

Answer 7

e.g eye or camera
inverted
diminished
real

e.g. projectors
inverted
magnified
real

e.g. magnifying glass
upright
magnified
virtual

Question 8

Magnification

Answer 8

m = image height/object height

= image distance/object distance

Question 9

CCDs

Answer 9

Grid of picture elements that store charge proportional to the light falling on them.
Wires read off the charges to form a digital image.

Question 10

Bits and Bytes

Answer 10

A bit is either a 1 or a 0
A byte is 8 bits
Decimal values can be represented by the number of various powers of 2 that make it up using 1s and 0s

Question 11

Relationship between number of bits and number of possible arrangements

Answer 11

N=2^b

b=log2(N)

Question 12

Resolution

Answer 12

Smallest distinguishable object distance on an image.

i.e. the distance represented by the width of each pixel

Question 13

Information in an image

Answer 13

Information in an image = (# of pixels) x (bits per pixel)

Question 14

Types of image processing

Answer 14

Changing brightness
Removing noise
Edge detection
Changing contrast

Question 15

Changing brightness

Answer 15

Increasing the value of each pixel until the brightest has the max value (usually 255)

Question 16

Removing noise

Answer 16

Replacing the value of each pixel with the mean or median of its value and the value of surrounding pixels

Question 17

Edge detection

Answer 17

Where adjacent pixels are subtracted to remove areas of uniform brightness and only pick out areas where the gradient of the brightness changes abruptly; e.g. at the edges

Question 18

Changing contrast

Answer 18

Spreading a narrow range of pixel values so the min is 0 and the max is 255 but in the same proportion

Question 19

Wave speed

Answer 19

speed = frequency x wavelength

Question 20

Frequency

Answer 20

Frequency = 1/Time period

Question 21

EM wavelength values (powers of 10 in m)

Answer 21

>6
radio
-1
microwave
-3
infrared
(700nm)
visible light
(400nm)
ultraviolet
-8
x-rays
-10 to -13
gamma rays

Question 22

EM waves

Answer 22

EM waves are waves of oscillating magnetic and electrical fields perpendicular to each other and the direction of travel
All EM waves can be polarised

Question 23

Unpolarised waves

Answer 23

Transverse oscillations in all planes

Question 24

Polarised waves

Answer 24

Once put through a polarising filter, waves oscillate in one plane

Question 25

Demonstrating polarisation

Answer 25

Putting light through a vertical and then a horizontal filter will result in no transmitted light
As polarised light is transmitted through another filter a detector behind it will see minimums and maximums every 90 degrees
Light can be polarised by shining a narrow beam through a tank of water containing a few drops of milk