Chapter 1

Question 1

What is the equation for the curvature of a circle?

Answer 1

curvature = 1/r

Question 2

What is the curvature when r = ∞?

Answer 2

0

Question 3

What are waves are called when they come from a very distance point?

Answer 3

Plane wave-fronts

Question 4

Light can be thought of as [ ] fronts or [ ]

Answer 4

Wave fronts

Rays

Question 5

Which way does a ray of light point?

Answer 5

Points along the direction of motion of the wave-front and is always at right-angles to the wave-front.

Question 6

Draw light from a small source and some from a very distant point. (Ray point of view)
Draw light from a small source and some from a very distant point. (Wave point of view)

Answer 6

See book. Pg 19

https://www.kerboodle.com/api/courses/15026/interactives/109567.html

Question 7

What is a converging lens?

Answer 7

A lens that focuses light to a point behind it. It can be used to concentrate light rays. In ray terms, the lens bends the parallel light rays focusing them together at the focus. In Wave terms, the lens works by altering the curvature of the waves so that they converge on a focus.

Question 8

What is the distance between the lens and the focus?

Answer 8

The radius of the wave fronts just after passing through the lens.
Focal Length, f

Question 9

How much curvature does a converging lens add?

Answer 9

1/f

Question 10

Lens power (D) =

Answer 10

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

Question 11

Why does a converging lens make an image of the source of light (object)?

Answer 11

Because light from every part of the object goes through the lens

Question 12

Curvature of waves leaving the lens =

Answer 12

curvature of waves entering it + curvature added by the lens

Question 13

What does v represent?

Answer 13

The distance from the lens to the image of the source

Question 14

What does u represent?

Answer 14

The distance from the lens to the source

Question 15

After passing through thee lens, the waves form part of [ ] centred on a point at distance [ ]. So the curvature of the waves leaving the lens = [ ] and the curvature of the waves entering the lens = [ ]

Answer 15

spheres
v
1/v
1/u

Question 16

1 / v =

Answer 16

1/v = 1/u + 1/f
(Lens maker’s equation)
NB: ‘u’ is negative like on a number line.

Question 17

What is the focal point? Focal length?

Answer 17

The point at which parallel waves from a very distance object are brought to focus.
The focal length is the distance from the centre of the lens to the focal point, and is a constant for a particular lens with a fixed shape.

Question 18

Waves from a nearer object are brought together …

Answer 18

beyond the focal point.

Question 19

The image distance v is [ ] than the focal length f, except for [ ]

Answer 19

greater

very distant objects

Question 20

Draw diagrams for a very distance object, an object just beyond the focus and an object at the focus

Answer 20

Pg 23

Question 21

What does it mean to magnify?

Answer 21

The size of the image appears larger than the original object.

Question 22

Linear magnification m =

Answer 22

Image height (m) / Object height (m)
or
Image distance v (m) / Object distance u (m)

Question 23

What does it mean if the magnification is negative?

Answer 23

The object is inverted

Question 24

Describe where an image is focused in a digital camera

Answer 24

light - sensitive microchip called a charge-coupled device (CCD)

Question 25

What is a CCD?

Answer 25

A screen covered by millions of tiny 'picture elements' called pixels

Question 26

Explain how pixels work

Answer 26

Each pixel stores electric charge when light falls on it - the brighter the light falling on the pixel, the greater the charge stored on it. The image becomes an array of numbers, which can then be manipulated to edit the image

Question 27

What is one bit of information?

Answer 27

One pixel simply records 'high' or 'low', then only one memory location storing a 1 or 0 is needed

Question 28

What colour colour scale is usually used?

Answer 28

256 grey-scale. From 0 (black) to 255 (white)

Question 29

What is a group of 8 bits called?

Answer 29

A byte

Question 30

How many bits do you need for a 256 grey-scale?

Answer 30

8

Question 31

Work out the binary representation of 5, 9, and 26

Answer 31

``` 5 = 0101 9 = 1001 26 = 11010 ```

Question 32

What is the equation for working out the number of arrangements of bits N? And working out the number of bits available b?

Answer 32

``` N = 2ᵇ b = log₂N ```

Question 33

Define Resolution

Answer 33

The scale of the smallest detail that can be distinguished.

Question 34

Resolution =

Answer 34

Width of object in image / No. of pixels across object

Question 35

Amount of information in an image =

Answer 35

No. of pixels * Bits per pixel

Question 36

Explain how to change the brightness of an image

Answer 36

A dim image can be brightened by increasing the value on each pixel by the same amount until the brightest pixel in the image is coded at 255

Question 37

Explain how to remove the noise of an image

Answer 37

Noise can be reduced by smoothing, where the value of each pixel is replaced with the median or mean of its value and those around it.

Question 38

Explain how to edge detect an image

Answer 38

To enhance edges in an image the average value of the pixel's neighbours is subtracted from each pixel. This removes uniform areas of brightness and picks out the places where the gradient of the brightness changes abruptly - at the edges

Question 39

Explain how to change the contrast of an image

Answer 39

An image with little contrast will not use the full range of pixel values. Eg, using the range 76-100. To improve the contrast this range is stretched across the 256 possible values so that the the value 76 becomes 0 and 100 becomes 255.

Question 40

What is noise in an image?

Answer 40

Noise in images refers to the random speckles across the image Unwanted interference affecting a signal

Question 41

Give an example of something with polarising lenses. Why do they have them?

Answer 41

Snow goggles and sunglasses. It dramatically cuts down the glare in bright environments

Question 42

``` Waves: Frequency f (Hz) = ```

Answer 42

1 / T | where T = time period (s)

Question 43

What is the speed of all electromagnetic waves?

Answer 43

c = 3.00 * 10⁸ m/s

Question 44

List the electromagnetic waves from largest to smallest and the wavelengths (m)

Answer 44

Radio (>10^6 - 10^-1), Micro- (10^-1 - 10^-3), Infrared (10^-3 - 7*10^-7), Visible (7-4 * 10^-7), Ultraviolet (4*10^-7 - 10^-8), X-rays (10^-8 - 10^-10), Gamma rays (10^-13 - <10^-16)

Question 45

Electromagnetic waves can be polarised. This is a property of [ ] waves.

Answer 45

Transverse

Question 46

Describe polarised and unpolarised transverse waves

Answer 46

Polarised: They vibrate in one plane only Unpolarised: Vibrate in randomly changing plane

Question 47

Electromagnetic waves are waves of [ ] magnetic and [ ]. The two fields are at right-angles to [ ] and to the [ ].

Answer 47

oscillating magnetic and electric fields | Each other and the direction of travel of the wave

Question 48

Can all electromagnetic waves be polarised?

Answer 48

Yes

Question 49

What does it mean if a wave is plane-polarised? Unpolarised?

Answer 49

The direction of oscillation remains fixed. | The direction of the oscillation will not be fixed

Question 50

Unpolarised light is polarised when it is passed through a [ ]

Answer 50

Polarising filter (look at the diagram on pg 31)

Question 51

How can you detect whether light has been polarised?

Answer 51

By observing it through a single polarising filter and rotating the filter. If the intensity of the light remains constant, the light source is emitting unpolarised light. If the intensity varies as the filter rotates, the source is emitting polarised light.

Question 52

How can you detect polarised radio waves?

Answer 52

By rotating the receiving aerial. The aerial will pick up the strongest signal when it is set up parallel to the plane of polarisation of the radio waves

Question 53

EM radiation is made up of ...

Answer 53

2 transverse waves vibrating in different directions

Question 54

Light that has passed through the polarising filter will only be vibrating in ...

Answer 54

One direction

Question 55

Describe microwaves going through a metal grille (Short)

Answer 55

The intensity drops to 0 when the wires are aligned with the direction of polarisation because the grille is absorbing the energy

Question 56

Describe microwaves going through a metal grille (Extended)

Answer 56

1) The virbrating electric field of the microwaves 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 those re-emitted waves are vibrating in the direction of the microwave receiver 4) The receiver only receives microwaves in one plane so even if the re-emitted waves travels towards the receiver it might not be picked up 5) When the wires and vibrations of waves are aligned, more electrons are excited than when they are at right angles to each other - all the energy is absorbed and the intensity reading drops to 0 6) When the wires and vibrations are at right angles to each other, some electrons in the grille are still excited and so there is a small drop in intensity

Question 57

How do converging lenses work?

Answer 57

They change the curvature of wavefronts by refraction It adds curvature. It curves the wavefronts by slowing down the light travelling through the middle of the lens more than lights at the edges All points on a wavefront take the same amount of time to reach the focus

Question 58

What is false colour used for?

Answer 58

Highlight certain features | Used in remote sensing of data

Question 59

How do you 'false colour'?

Answer 59

False colour is where you add different values to different colour values in order to accentuate that feature colour