City University, London. Foundation to Engineering Programme
Science Assignment. Submit by Monday November 20 2017
Attempt all Sections. Weighting 30% of Science Unit Marks.
Section 6 Semiconductor Devices
(A) A Germanium atom has 4 valence electrons.
(i) What property can be determined by valence electrons? [1 Mark]
(ii) Explain, with the aid of a sketch, how COVALENT bonds hold Germanium
atoms within a crystal structure. [2 Marks]
(iii) Describe how a p type extrinsic Germanium semiconductor material is
produced. [2 Marks]
(iv) In a PN semiconductor diode, what is the depletion region?
With reference to the depletion region, how does a PN semiconductor diode
function in forward and reverse bias modes? [4 Marks]
(v) Draw the voltage–current characteristic for the COMPLETE DIODE model.
Explain, with the aid of equivalent forward and reverse bias electrical circuits
how the COMPLETE DIODE is derived.
Fully label the characteristic and equivalent circuits. [5 Marks]
(B) RESEARCH Question.
The Science Museum has a few electronic devices displays.
(i) Describe how aLIQUID CRYSTAL is produced.
Explain how liquid crystals are used in displays. [5 Marks]
(ii) Describe how RARE EARTH MAGNETS are produced.
Describe 2 uses of rare earth magnets. . [5 Marks]
(C) Section 5 Electromagnetic Waves
(i) Explain how electromagnetic waves are produced and transmitted. . [4 Marks]
(ii) What are transverse waves and longitudinal waves?
(iii) In what fundamental way does a sound wave differ from an electromagnetic wave? [2 marks]
(D) Section4 Waves
(i) Explain the phenomenon of the Doppler effect in Waves
(ii) How does the phenomenon of the Doppler Effect differ between sound and electromagnetic (EM) waves? [3 marks]
(iii) For EM waves, with a source speed u that is small compared to c, the observed frequency f ’ from a source with frequency f is given by:
f ' = f (1 ± u/c)
What do the above statement and corresponding equation describe?
[3 Marks]
(E) Intensity of Sound
A point source of sound that emits uniformly in all directions is located in
the middle of a large, open field.
The intensity of sound at a distance r1 directly north of the source is I1.
The intensity of sound at a distance r2 directly west of the source is I2.
Explain whyI2 = (r1/r2 )2. I1 [3 Marks]
-2-
(F) Section 2 Vectors
Vector has a magnitude of 20 units and points in the positive x direction.
A second vector, has a magnitude of 45 units and points at an angle
Ф = -65o below the positive x axis. ( see Figure 1 below)
_
A= 20 units, Ф = -65o
Figure 1 _
( Not to scale) B = 45units
(i) Measure, by drawing a vector diagram to scale, the resultant of A and B.
(ie Determine the magnitude and angle of the resultant by completing the
parallelogram). [5 Marks]
_ _
(ii) By measurement, which vector A or B has the greater xcomponent.
[1 Marks]
(iii) Use the horizontal and vertical component method to confirm your
answers in parts (i) and (ii). [3 Marks]