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A2-Phys-23-2-A1 > 1: Imaging_checked > Flashcards

1: Imaging_checked Flashcards

1
Q

Define Frequency

A

The number of whole vibrations (or oscillations), f, passing a given point each second.

Frequency is measured in Hertz, Hz

The frequency is the inverse of the period

f = 1/T

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2
Q

Define Period

A

The time, T, taken for a whole vibration (oscillation)

Unit of Period is ‘second’, s

The frequency is the inverse of the period

f = 1/T

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3
Q

Define Phase Difference

A

The amount by which one wave lags behind another wave.

Phase difference is measured in degrees or radians

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4
Q

What do lenses do?

A

Lenses change the curvature of the incident wavefront by refraction.

A lens adds curvature to waves as they pass through it. If waves are uncurved before passing through the lens, and parallel to the lens axis, they will be given spherical curvature, centred on the focus (or focal point) of the lens.

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5
Q

Explain how a converging lens curves wavefronts by changing the speed of the wave

A

A converging lens curves the wavefronts by slowing down the part of the wave (or light) travelling through the middle of the lens more than parts of wave (or light) at the lens edges.

All points on a wavefront take the same amount of time to get to the focus point.

The more powerful (thicker) the lens, the more it will curve the wavefronts that travel through it - so the shorter its focal length

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6
Q

What is the focal length?

A

The focal length, f, is the distance between the lens axis and the focus

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7
Q

What is the lens power equation (D)?

A

lens power = 1 / f (focal length in metres)

Lens power is measured in Dioptres

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8
Q

What is the curvature of wave equation

A

Curvature = 1 / r

(radius or distance in metres)

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9
Q

What is the lensmaker equation words and symbols?

A

The lens equation states: curvature of waves leaving lens = curvature of waves before entering lens + curvature added by lens

1/v = 1/u + 1/f

  • v = image distance (lens to image formed)
  • u = object distance (lens to source)
  • f = focal length
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10
Q

why is object distance (1/u) negative

A

You always measure distances from the lens axis, and count distances to the right as poitive; and distances to the left as negative

(Just like drawing graphs)

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11
Q

Describe the wavefronts of a distant light source. What curvature will a converging lens give them

A

If you’ve got a distant light source, the wavefronts approaching the converging lens will be flat (1/u = 0)

The converging lens will then give them a curvature of 1/f

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12
Q

Describe the wavefronts if the source is at the focus of the lens

A

If the source is at the focus of the lens, the wavefronts will start off curved w/ negative curvature.

This is because u is measured as a negative distance.

This -ve curvature is then cancelled out by the +ve curvature added by the converging lens - so the wavefronts will be made flat

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13
Q

What are the linear magnification equations for height and distance

A

linear magnification =

image height (m) / object height (m)

image distance (m) / object distance (m)

v/u

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14
Q

What is a bit?

A

A single binary digit {i.e. 0 or 1}

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15
Q

What is a byte?

A

A byte is a group of 8 bits

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16
Q

What is a pixel?

A

A pixel is the smallest unit of a digital image or graphic that can be displayed and represented on a digital display device.

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17
Q

What is the equation for number of arrangements [or alternatives] of bits(b)?

A

N = 2b

  • N = number of levels or alternatives ot arrangements
  • b = number of bits
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18
Q

How do you calculate number of bits, b, from number of arrangements N?

A

b = log2N

  • b = number of bits
  • N = number of levels or alternatives or arrangements
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19
Q

What is the equation to calculate image resolution?

A

Resolution = width of image / number of pixels across object

Resolution is measured in metres per pixel [mpixel-1]

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20
Q

What is the equation to calculate amount of information in an image?

A

Amount of information = total number of pixels * bits per pixel

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21
Q

In processing a digital image, what does adding a fixed number to each value of a pixel do?

A

Adding a fixed number to each value of pixel increases the brightness (if the fixed number is +ve) - each pixel has a higher number therefore has a lighter colour.

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22
Q

How do you increase the brightness of a digital image? What is the effect of this

A

Add a fixed number value to each pixel. This produces a lighter coloured image

23
Q

In digital image processing, what does multiplying each value of a pixel, by a fixed number, do?

A

Muliplying each value of pixel by a fixed number > 1 increase/improves the contrast. It also makes the processed image brighter/lighter

24
Q

How do you increase the contrast of an image effect?

A

Multiply the value of each pixel with a number greater than one, this will affect bigger numbers more than smaller numbers, increasing the contrast and so making the image more vivid

25
Q

What is noise in the context of images

A

Noise is random unwanted interference across the image. This is usually shown as bright or dark spots on the image

26
Q

Describe how to remove noise on an image.

Which is better for this, median or mean?

A

Replace each pixel with the median of itself and the 8 pixels surrounding it.

The result is that any ‘odd’ (very high/low values are removed and the image is made smoother)

Using the median instead of the mean when replacing values is better; as replacing each pixel by the mean of itself and surrounding pixels isn’t as good because the ‘odd’ value affects the new value.

27
Q

How do you carry out edge detection?

A

The Laplace rule is a method of finding edges.

Multiply the value of a pixel by four, and then subtract the value of pixels to the N, S, W and E. If the value is negative, then the pixel is treated as if its value is zero {i.e. black}

Edge detected images are usually then inverted so that white becomes black and vice versa.

The result is that any pixel not on an edge goes white, so you’re left with just the edges.

28
Q

What is the equation for wave velocity how to calculate frequency?

A

Wave velocity = frequency * wavelength

Frequency = 1 / time period

29
Q

Describe a longitudinal wave, give an example

A

In longitudinal waves, the vibrations are along the wave’s direction of travel

Example of longitudianl wave: Sound

30
Q

Describe a transverse wave

A

The vibration is at a right angles to the waves direction of travel.

Example of transverse waves: electromagnetic waves

31
Q

What is an electromagnetic wave made of?

A

Electromagnetic waves are transverse waves consisting of electric and magnetic fields oscillating at right angles

32
Q

Property of electromagnetic waves?

A

EM waves can be polarised

33
Q

What is the defining characteristic of a polarised wave? Give an example

A

Polarized waves are EM waves in which the vibrations occur in a single plane.

The process of transforming unpolarized light into polarized light is known as polarization

Only transverse waves can be polarised

34
Q

What is an indication that light is a transverse wave?

A

The fact it can be polarised - only transverse waves can be polarised

35
Q

How do you investigate polarising microwaves?

A
  1. Put a metal grille between the microwave transmitter and receiver
  2. The intensity of the microwaves is at a maximum when the direction of the vibration of the microwaves and the wires are at right angles to each other
  3. As you rotate the grille, the intensity decreases, so the reading on the voltmeter (connected to receiver) decreases
  4. When the wires of the grilare alignedle with the direction of the polarised waves, no signal will the shown on the voltmeter because the metal grille will absorb the energy of the wave
36
Q

Explain what happens when microwaves pass through a grille

A
  1. The vibrating electric field of the microwave excites electrons in the metal grille
  2. The energy of the incoming microwaves is absorbed by the grille and re-emitted in all directions
  3. Only a few of the re-emitted waves are vibrating in the direction of the receiver
  4. The receiver only receives waves in one plane, so even if the re-emitted wave travels toward the receiver, it might not be picked up
  5. When the wires of the grille and the vibrations of the wave are aligned, more electrons are excited than when they’re at right angles to each other - all the energy is absorbed and the intensity reading drops to zero.
  6. When the wires & vibrations are at right angles to each other, some electrons in the grille are still excited so there is still a small drop in intensity
37
Q

Why do you only need one grilleª when investigating the polarisation of microwaves?

A

The microwave transmitter transmits polarised waves so you only need one grille

38
Q

Explain why how and why the intensity of the microwaves changes when the metal grille is rotated.

A
  1. When wires and vibrations are aligned, more electrons are excited than when they’re at right angles to each other - all the energy is absorbed and the intensity reading drops to 0
  2. When the wires and vibrations are at right angles, some electrons in the grille are still excited and so there is still a small drop in intensity
39
Q

Why does the intensity drop to 0 when the wires are aligned to the direction of polarisation of the microwaves?

A

The grille is absorbing their energy

40
Q

Why can you not polarise microwaves using a polarising filter? How do you polarise them?

A

The wavelength of the microswaves is too long.

Metal grilles can be used to polarise microwaves instead

41
Q

State 2 examples of polarising filters

A
  1. 3D films use polarised light to create depth- the filters in each lens are at right angles to each other, so, each eye gets a slightly different picture
  2. Polaroid sunglasses use polarising filters - reflected light is partially polarised so the sunglasses block out some light to prevent glare
42
Q

What happens if you try to pass light through 2 polarising filters at right angles to each other?

A

No light will get though, all directions of vibration will be blocked

43
Q

Describe how you would investigate the polarisation of light using 2 polarising filters

A
  1. Align the transmission axes of 2 polarising filters so they are both vertical. Shine unpolarised light on the first filter. Keep the position of the first filter fixed and rotate the second one
  2. Light that passes through the first filter will be vertically polarised
  3. As you rotate the 2nd filter, the amount of light that passes through the second filter varies:
  4. When the 2nd polariser is displaced from 0deg to 90deg - the intensity will drop from a maximum to zero;
  5. As the filter is displaced from 90deg to 180deg the intensity will increase again from 0 to a maximum at 180deg; from 180 to 270 deg: max to zero; 270deg to 360deg: zero to max
44
Q

What is approximate value for radiowave wavelength?

A

Approximate wavelength range for radiowaves: 106m to 10-1m

45
Q

What is the approx value for microwave wavelength?

A

Approximate wavelength range for microwaves: 10-1m to 10-3m

46
Q

What is the approx value for infrared wavelength?

A

The infrared range of wavelength is: 10-3m to 7 x 10-7m

47
Q

What is the approx value for visible light wavelength?

A

The visible wavelngth range is: 7x10-7m to 4x10-7m

48
Q

What is the approx range for uv light wavelength?

A

Range: 4 x 10-7m to 10-8m

49
Q

What is the approx range for x-ray wavelength?

A

X-ray wavelength range: 10-8m to 10-13m

50
Q

What is the approx range for gamma ray wavelength?

A

Gamma wavelength range: 10-10m to 10-16m

51
Q

how to remember EM spectrum

A

Rich Men In Vegas Use Save Xpensive Gifts

52
Q

why is 1/u the negative of 1/v?

A

when 1/v = 0, 1/f = -1/u + 0 -> 1/f = -1/u

when 1/u = 0, 1/f = 1/v + 0 -> 1/f = 1/v

53
Q

Intensity of a wave equation

A

Intensity of a wave

I=P/A
I = intensity (W/m^2)
P = Power (W)
A = Area (m^2)

A2-Phys-23-2-A1 (61 decks)

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