2: Exam Questions

Question 1

Calculating ratio, distance to A/distance to B (based on a given picture)

Answer 1

Image size ∝ 1/distance

Question 2

Explaining minimum sampling freq.

Answer 2

high f are missed, aliases appear

Question 3

Explaining why using only ‘x’ bits is sufficient

Answer 3

extra info is about details in noise not details in signal

Question 4

Advantage and Disadvantage of using wider freq. range

Answer 4

Ad) higher quality speech, Dis) greater bandwidth

Question 5

Digital samples can differ from the original analogue signals. How can you reduce that error?

Answer 5

1) more bits (per sample) 2) more sampling levels

Question 6

Explain why something can take longer to download than calculated

Answer 6

more information has to be sent
explanation : possible bottleneck in named part of system /
recognise possible need for error checking /

Question 7

Explain why a laptop will fail to communicate reliably with a hub beyond a certain distance. Consider signal strength and noise

Answer 7

signal decreases in amplitude as it spreads /
covers a wider area / signal gets absorbed by walls etc. ;
radio noise is present in environment ;
signal / noise ratio decreases as distance from hub
increases ;
noise may trigger false bits / degrade the signal
information / data link becomes inaccurate

Question 8

A single musical note is played on an oboe. Amplitude against time graph given (regular large peaks with lots of ‘wiggles’ between large peaks):
State how the waveform shows that the note has a definite pitch but that it also contains more than 1 freq. component [2]

Answer 8

waveform is periodic / (main peaks) repeats itself regularly ;

but more complex than pure sine wave / has harmonics /
higher frequency (oscillations) / other (smaller) oscillations /
smaller peaks (between large ones)

Question 9

Describe how you would estimate the bandwidth needed for transmitting the digitised information (freq. given, bits per sample given)

Answer 9

bandwidth ≈ bit rate / ≈ bit rate /2

bit rate = sampling frequency x bits per sample

Question 10

[1] state what is meant by the resolution of a measuring instrument

Answer 10

smallest difference that can be detected

Question 11

[1] One application of an ammeter is to monitor a current to check that it does not suddenly increase to a much larger value. Explain why the analogue ammeter may be a better choice than the digital ammeter

Answer 11

Easier to see sudden movement of needle than changes in

digits/ digital meter samples/has time lag (1)

Question 12

Suggest why an ammeter for use in circuits carrying large currents should have a very low resistance [1]

Answer 12

one of:
Idea of not affecting the measurement (1);
Meter will overheat and could be damaged (1);
smaller p.d. drop across the resistor (1)