Chapter 1

Question 1

What is the equation for the curvature of a circle?

Answer 1

Curvature = 1/r

Question 2

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

Answer 2

Plane wave-fronts

Question 3

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

Answer 3

Wave

Rays

Question 4

What is the distance between the lens and the focus?

Answer 4

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

Question 5

How much curvature does a converging lens add?

Answer 5

1/f

Question 6

Lens power (D) =

Answer 6

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

Question 7

1 / v =

Answer 7

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

Question 8

Waves from a nearer object are brought together …

Answer 8

beyond the focal point.

Question 9

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

Answer 9

greater

very distant objects

Question 10

What does it mean to magnify?

Answer 10

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

Question 11

Linear magnification m =

Answer 11

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

Question 12

What does it mean if the magnification is negative?

Answer 12

The object is inverted

Question 13

Describe where an image is focused in a digital camera.

Answer 13

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

Question 14

What is a CCD?

Answer 14

A screen covered by millions of tiny ‘picture elements’ called pixels

Question 15

Explain how pixels work

Answer 15

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 16

What is one bit of information?

Answer 16

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

Question 17

What colour scale is usually used?

Answer 17

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

Question 18

What is a group of 8 bits called?

Answer 18

A byte

Question 19

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

Answer 19

8

Question 20

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

Answer 20

N = 2ᵇ
b = log₂N

Question 21

Define Resolution

Answer 21

The scale of the smallest detail that can be distinguished.

Question 22

Resolution =

Answer 22

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

Question 23

Amount of information in an image =

Answer 23

No. of pixels * Bits per pixel

Question 24

Explain how to change the brightness of an image

Answer 24

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 25

Explain how to remove the noise of an image

Answer 25

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 26

Explain how to edge detect an image

Answer 26

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 27

Explain how to change the contrast of an image

Answer 27

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 28

What is noise in an image?

Answer 28

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

Question 29

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

Answer 29

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

Question 30

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

Answer 30

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

Question 31

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

Answer 31

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 32

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

Answer 32

Transverse.

Question 33

Describe polarised and unpolarised transverse waves

Answer 33

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

Question 34

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

Answer 34

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

Question 35

Can all electromagnetic waves be polarised?

Answer 35

Yes.

Question 36

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

Answer 36

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

Question 37

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

Answer 37

Polarising filter.

Question 38

How can you detect whether light has been polarised?

Answer 38

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 39

How can you detect polarised radio waves?

Answer 39

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 40

EM radiation is made up of ...

Answer 40

2 transverse waves vibrating in different directions.

Question 41

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

Answer 41

One direction.