1). (a) Explain what is meant by the Binary
number system.
(b) Explain
why the binary number system is very important for digital electronic
systems
2) The
table below contains both decimal and binary numbers.
Complete
the table by giving the equivalent binary or decimal number.
The
first row is completed for you as an example.

Decimal Number

Binary Number

(a)

8

01000

(b)

4


(c)


10100

(d)


00110

(e)

15


(f)

28


(g)


11001

(h)

19


3). (a) Show, by calculation, that if the tape
speed of a C90 Compact Cassette was
47.6mms^{1} then there would be approximately 130m of tape in
the cassette.
(b) When all of the tape is spooled onto the
one reel, its outer radius is 26mm and its
inner radius is 12mm.
Estimate, by calculation, the thickness
of the tape.
4). (a) Explain two advantages of storing
information digitally.
(b) Explain one disadvantage of storing
information digitally.
5). (a) State three devices which can store
digital information and give their approximate
capacity
(b) A typical portable digital storage
device has a capacity of 4GB. If average
size of
an MP3 music file is 5MB, estimate, by calculation, how many
music files can be
stored on this
devic
(c) How many CDs would be required to hold
the same amount of information
6). (a) Draw a labelled diagram to represents
the vertical crosssection through a CD.
(b) Explain briefly how
information is stored on a CD.
(c) Explain why a DVD will store more
information than a CD even though they are
physically the same size.
7). (a) The wavelength, in air, of the light
used to read a DVD is 650nm. If the
refractive
index of the
polycarbonate coating on the bottom of a DVD is 1.56, calculate the
wavelength of the light in the
polycarbonate coating.
(b) If destructive interference is to occur
with the light reflected from an island on a
DVD,calculate the
height of the island.
8). (a) The radius of the inner track on a CD is
22mm and the outer track is 58mm.
Calculate the area
of the CD that is used for storing data.
(b) If the spiral tracks are 1.6µm apart,
estimate the length of the spiral that is used to
store the data.
(c) If 700MB of data is to be stored on a
CD, estimate the minimum length of an island.
(d) In practice the minimum length of a
island is 830nm. Why is this value
smaller
than the calculated value in part (c).
9). The
storage of information digitally is causing many issues including those listed
below:
Storage,
Cataloguing, Moral, Ethical, Piracy, Data centres, Waste and Back up of data.
Prepare
a presentation which you could deliver to local business leaders highlighting
what you consider to be the three key
issues facing society associated with the digital storage of information.
The following responses are intended to act
as a guide for staff and students.
1). (a) Base 2 number system
(b) Enables circuits to represent numbers
based on whether they are on or off, corresponding to 1 and 0
2).

Decimal Number

Binary Number

(a)

8

01000

(b)

4

00100

(c)

20

10100

(d)

6

00110

(e)

15

01111

(f)

28

11100

(g)

25

11001

(h)

19

10011

3). (a) C90 plays for 45 minutes each side =
2700s
=>
130/0.0476 = 2731s
(b) Mean radius of tape on spool is (26 +
12) / 2 = 19mm
=>
Circumference of mean radius = 2p19 =
119.38mm
=>
Number of circles of tape = 130/0.11938 = 1089
Now
width of tape on spool = 26 – 12 = 14mm
=>
Thickness of tape = 14 / 1089 = 0.0129mm
4). (a) Can be easily copied for back ups, does
not degrade, can be encrypted etc
(b) Difficult to completely delete, easily
copied etc
5). (a) Responses to this will have to adapt to
technology. Currently examples might
include:
floppy
disk = 1.44MB
CD
= 700MB
DVD
= 4.7GB
(b) 4000 / 5 » 800 music files
(c) 4000 / 700 = 5.7 => 6CDs
6). (a) See support materials
(b) On a spiral track as a series of bumps
or islands (pits) representing binary numbers.
(c) Tracks can be closer together and the
islands can be smaller since they are scanned
by a shorter
wavelength laser.
7). (a) 650 / 1.56 = 417nm
(b) For destructive interference the path
difference should be l/2, so
therefore the
height of the
island should be l/4.
So island height is 417 / 4 = 104.25nm
8). (a) p58^{2}  p22^{2}
= 9048mm^{2}
(b) Mean radius of spiral = (58 + 22) / 2 =
40mm
Circumference
of mean track is 2p40 = 251.33mm
=>
Area of mean track is 251.33 × 0.0016 = 0.4mm^{2}
=>
Number of circular tracks = 9048 / 0.4 = 22620
=>
Taking the mean circumference total length = 22620 × 251.33 » 5.685km
(c) 700MB = 700 × 2^{20} × 8 =
5872025600 bits.
=>
5685 / 5872025600 = 0.968µm
(d) land region needed between the islands,
error correction, block headers etc
9). Appropriate
presentation dealing with the three key issues facing society associated with
the digital storage of information.