Solve problems involving the conversion between binary numbers and decimal numbers. Students should be aware of the term bit. An awareness of the least-significant bit (LSB) and most-significant bit (MSB) is required. Problems will be limited to a maximum of five bits in digital numbers.
14.1.2
Describe different means of storage of information in both analogue and digital forms. Students may consider LPs, cassette tapes, floppy disks, hard disks, CDs, DVDs, and so on.
14.1.3
Explain how interference of light is used to recover information stored on a CD. Students must know that destructive interference occurs when light is reflected from the edge of a pit.
14.1.4
Calculate an appropriate depth for a pit from the wavelength of the laser light.
14.1.5
Solve problems on CDs and DVDs related to data storage capacity.
14.1.6
Discuss the advantage of the storage of information in digital rather than analogue form. Students should consider quality, reproducibility, retrieval speed, portability of stored data and manipulation of data.
14.1.7
Discuss the implications for society of ever-increasing capability of data storage. Teachers should consider moral, ethical, social, economic and environmental implications.
14.2
Data capture; digital imaging using charge-coupled devices (CCDs)
4
14.2.1
Define capacitance.
14.2.2
Describe the structure of a charge-coupled device (CCD). Students should know that a CCD is a silicon chip divided into small areas called pixels. Each pixel can be considered to behave as a capacitor.
14.2.3
Explain how incident light causes charge to build up within a pixel. Students are required to use the photoelectric effect.
14.2.4
Outline how the image on a CCD is digitized. Students are only required to know that an electrode measures the potential difference developed across each pixel and this is then converted into a digital signal. The pixel position is also stored.
14.2.5
Define quantum efficiency of a pixel. Quantum efficiency is the ratio of the number of photoelectrons emitted to the number of photons incident on the pixel.
14.2.6
Define magnification. Students are required to know that magnification is the ratio of the length of the image on the CCD to the length of the object.
14.2.7
State that two points on an object may be just resolved on a CCD if the images of the points are at least two pixels apart.
14.2.8
Discuss the effects of quantum efficiency, magnification and resolution on the quality of the processed image.
14.2.9
Describe a range of practical uses of a CCD, and list some advantages compared with the use of film. Students should appreciate that CCDs are used for image capturing in a large range of the electromagnetic spectrum. They should consider items such as digital cameras, video cameras, telescopes, including the Hubble Telescope, and medical X-ray imaging.
14.2.10
Outline how the image stored in a CCD is retrieved.
