Chapter 1 Flashcards
What is the equation for the curvature of a circle?
Curvature = 1/r
What are waves are called when they come from a very distant point?
Plane wave-fronts
Light can be thought of as [ ] fronts or [ ]
Wave
Rays
What is the distance between the lens and the focus?
The radius of the wave fronts just after passing through the lens.
Focal Length, f
How much curvature does a converging lens add?
1/f
Lens power (D) =
Lens power (D) = 1 / focal length (m)
1 / v =
1/v = 1/u + 1/f
(Lens maker’s equation)
NB: ‘u’ is negative like on a number line.
Waves from a nearer object are brought together …
beyond the focal point.
The image distance v is [ ] than the focal length f, except for [ ]
greater
very distant objects
What does it mean to magnify?
The size of the image appears larger than the original object.
Linear magnification m =
mage height (m) / Object height (m)
or
Image distance v (m) / Object distance u (m)
What does it mean if the magnification is negative?
The object is inverted
Describe where an image is focused in a digital camera.
light - sensitive microchip called a charge-coupled device (CCD)
What is a CCD?
A screen covered by millions of tiny ‘picture elements’ called pixels
Explain how pixels work
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.
What is one bit of information?
One pixel simply records ‘high’ or ‘low’, then only one memory location storing a 1 or 0 is needed
What colour scale is usually used?
256 grey-scale. From 0 (black) to 255 (white)
What is a group of 8 bits called?
A byte
How many bits do you need for a 256 grey-scale?
8
What is the equation for working out the number of arrangements of bits N? And working out the number of bits available b?
N = 2ᵇ b = log₂N
Define Resolution
The scale of the smallest detail that can be distinguished.
Resolution =
Width of object in image / No. of pixels across object
Amount of information in an image =
No. of pixels * Bits per pixel
Explain how to change the brightness of an image
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.
Explain how to remove the noise of an image
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.
Explain how to edge detect an image
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.
Explain how to change the contrast of an image
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.
What is noise in an image?
Noise in images refers to the random speckles across the image
Unwanted interference affecting a signal
Give an example of something with polarising lenses. Why do they have them?
Snow goggles and sunglasses. It dramatically cuts down the glare in bright environments.
Waves: Frequency f (Hz) =
1 / T
where T = time period (s)
List the electromagnetic waves from largest to smallest and the wavelengths (m)
Radio (>10^6 - 10^-1), Micro- (10^-1 - 10^-3), Infrared (10^-3 - 710^-7), Visible (7-4 * 10^-7), Ultraviolet (410^-7 - 10^-8), X-rays (10^-8 - 10^-10), Gamma rays (10^-13 - <10^-16)
Electromagnetic waves can be polarised. This is a property of [ ] waves.
Transverse.
Describe polarised and unpolarised transverse waves
Polarised: They vibrate in one plane only
Unpolarised: Vibrate in randomly changing plane
Electromagnetic waves are waves of [ ] magnetic and [ ]. The two fields are at right-angles to [ ] and to the [ ].
oscillating electric
Each other and the direction of travel of the wave
Can all electromagnetic waves be polarised?
Yes.
What does it mean if a wave is plane-polarised? Unpolarised?
The direction of oscillation remains fixed.
The direction of the oscillation will not be fixed.
Unpolarised light is polarised when it is passed through a [ ]
Polarising filter.
How can you detect whether light has been polarised?
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.
How can you detect polarised radio waves?
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.
EM radiation is made up of …
2 transverse waves vibrating in different directions.
Light that has passed through the polarising filter will only be vibrating in …
One direction.
