ELECTRONIC AND ELECTRICAL FUNDAMENTALS
Section A
Attempt all the questions in this section (50 marks)
1.
Convert the following numbers.
(
a
)
Binary to Decimal
11101001
2
(
b
)
Hexadecimal to Binary
E4
16
(
c
)
Decimal to Hexadecimal
215
10
2.
Identify the circuit symbols shown in Figure Q2(
a
) and Figure Q2(
b
).
(
a
)
Figure Q2(
a
)
(
b
)
Figure Q2(
b
)
3.
Determine the logic input X and Y for the gates shown in Figure Q3(
a
) and
Figure Q3(
b
) respectively.
(
a
)
X
1
1
Figure Q3(
a
)
(
b
)
0
Y
0
Figure Q3(
b
)
4.
Figure Q4 shows a current carrying conductor placed between magnetic poles.
The magnetic flux density is 0·2 Tesla. The conductor experiences a force of 1·2
N
when the current is 15
A.
N
S
Figure Q4
(
a
)
Determine the length of conductor within the magnetic field.
(
b
)
State what happens to the force when the current direction is reversed.
5.
Referring to Figure Q5, and using the supplied datasheet:
V
IN
330
?
RED
LED
L424 HDT
Figure Q5
(
a
)
state the purpose of the series resistor;
(
b
)
state the maximum forward current the diode can handle;
(
c
)
state the typical forward voltage drop;
(
d
)
determine the maximum value of input voltage that can be safely applied.
6.
A generator produces a sinusoidal current represented by the equation
i
= 12sin
?
amperes
Determine:
(
a
)
the maximum value of the current;
(
b
)
the r.m.s. value of the current;
(
c
)
the average value of the current;
(
d
)
the instantaneous value of the current when
?
= 30°.
7.
With reference to the circuit shown in Figure Q7, in which resistor R
1
is 10
k
?
and
R
V
can be varied between 5
k
?
and 15
k
?
:
V
0
100
mV
R
1
R
V
Figure Q7
(
a
)
name the circuit configuration;
(
b
)
determine the output voltage when R
V
is set to 10
k
?
;
(
c
)
determine the maximum possible output voltage when the input is 100
mV;
(
d
)
determine the minimum possible output voltage when the input is 100
mV.
8.
With reference to the circuit shown in Figure Q8:
3
?
2
A
10
?
18
V
12
V
R
Figure Q8
(
a
)
determine the voltage across the 3
?
resistor;
(
b
)
determine the current through the 10
?
resistor;
(
c
)
determine the value of resistor R.
(
d
)
A fault condition causes the 10
?
resistor to be open circuit. Determine the
new value of supply current.
9.
For the circuit shown in Figure Q9:
A
B
C
Z
Figure Q9
(
a
)
determine the Boolean expression for output Z;
(
b
)
draw the truth table for the circuit;
(
c
)
determine the circuit output Z when a faulty condition causes the output of the
invertor to be permanently low (logic 0).
[Turn over for Section B on
Section B
Attempt any TWO questions in this section (50 marks)
Each question is worth 25 marks
10.
(
a
)
State the logic output for the logic gates shown in Figure Q10(
a
)(i) and
Figure Q10(
a
)(ii).
(i)
1
0
Z=
1
Figure Q10(
a
)(i)
(ii)
1
0
Z=
1
Figure Q10(
a
)(ii)
(
b
)
Add the following binary numbers.
(i)
0101
2
+ 0101
2
(ii)
0010
2
+ 0101
2
(
c
)
Draw the logic circuit for the expression
Z = A.B + A
¯
.C
(
d
)
Determine the logic expression for the logic circuit shown in Figure Q10(
d
).
A
Z=
B
A
C
=
1
&
=
1
Figure Q10(
d
10.
(continued)
(
e
)
Figure Q10(
e
)(i) shows a logic circuit.
1
R
S
T
4
2
5
Z=
3
Figure Q10(
e
)(i)
(i)
Determine the logic expression for the circuit.
(ii)
Draw the truth table for the circuit.
(iii)
The circuit shown in Figure Q10(
e
)(i) has developed a fault, and upon
testing the outputs shown in the truth table Figure Q10(
e
)(iii) were
obtained. Explain which gate (input or output) is at fault and state the
nature of the fault.
R
S
T
Z
0
0
0
1
0
0
1
1
0
1
0
1
0
1
1
0
1
0
0
1
1
0
1
1
1
1
0
0
1
1
1
0
Figure Q10(
e
)(iii)
11.
(
a
)
For the circuit shown in Figure Q11(
a
), determine:
R
1
1
A
8A
V
S
2
A
20
A
R
3
R
5
R
6
R
7
R
4
R
2
Figure Q11(
a
)
(i)
the current flowing in R
3
;
(ii)
the current flowing in R
6
.
(
b
)
For the circuit shown in Figure Q11(
b
), determine:
R
1
1
A
10
?
20
?
10
?
20
?
V
S
4
A
3
A
R
3
R
5
R
6
R
7
R
4
R
2
Figure Q11(
b
)
(i)
the voltage drop across R
7
;
(ii)
the supply voltage;
(iii)
the power dissipated in R
7
;
(iv)
the energy consumed in 3 hours by the branch containing R
2
& R
4
.
(
c
)
A variable speed, 10
kW generator produces an output voltage of 120
V, has a
flux density of 40 milliTesla, and a conductor length of 25
m. Calculate:
(i)
the speed of the generator;
(ii)
the speed of the generator when the output voltage is 200
V;
(iii)
the maximum current the generator can supply when the output is 200
V.
(
d
)
A conductor is forced to move downwards within a magnetic field, as shown in
Figure Q11(
d
).
N
S
Figure Q11(
d
)
(i)
State the formula used to calculate the current in the conductor.
(ii)
Explain how the direction of the current can be determined.
12.
(
a
)
For the circuits shown in Figures Q12(
a
)(i) and (ii) the input voltage is
12
V
pk–pk
, 50
Hz in each circuit.
(i)
Assuming that the switch remains open, sketch the input and output
waveforms for the circuit shown in Figure 12(
a
)(i), clearly indicating the
differences between the input waveform and the output waveform.
D1
C1
V
OUT
12
V
pk–pk
R
L
Figure Q12(
a
)(i)
(ii)
Sketch the output waveform for the circuit shown in Figure 12(
a
)(ii),
clearly indicating the differences between the new output waveform and
the output waveform of Figure Q12(
a
)(i).
D1
12
V
pk–pk
D4
R
L
D2
D3
Figure Q12(
a
)(ii)
12.
(continued)
(
b
)
For the circuit shown in Figure Q12(
b
):
R
v
R
i
V
IN
=
2
V pk–pk
R
f
=100
K
V
OUT
5
Circuit
Gain = -5
1
Figure Q12(
b
)
(i)
state the circuit configuration;
(ii)
determine the output voltage;
(iii)
determine the value of R
i
;
(iv)
explain the purpose of R
v
.
(
c
)
(i)
Identify the circuit shown in Figure Q12(
c
).
(ii)
With reference to Figure Q12(
c
), identify the purpose of each of the
following components: R
1
& R
2
, C
2
& C
3
.
R
1
Ideal
Transistor
Gain = 500
R
3
C
2
1K5
I
C
R
2
R
4
C
3
6K8
1·4
V
6
V
0
V
V
CC
12
V
C
1
Figure Q12(
c
)
(iii)
Calculate the output voltage for the circuit shown in Figure Q12(
c
) when
the input voltage is 20
mV
pk–pk
.
[Turn over for Question 12(c) continued on
12.
(
c
)
(continued)
(iv)
When the input voltage is increased to 40
mV
pk–pk
the output waveform
is as shown in Figure Q12(
c
)(iv).
V
OUT
+6
V
-6
V
0
V
t (secs)
Figure Q12(
c
)(iv)
Explain why the shape of the waveform is non-sinusoidal.
(v)
Suggest two ways of preventing this.
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