Download Unit BS113 Electrical and Electronic Technology

Unit BS113 Electrical and Electronic Technology
What you will be expected to know and do in the exam
To know
The basic idea of an electric circuit.
Ohm's Law and Kirchhoff's Laws.
Alternating current and voltage and the
power in a.c. circuits.
Electrical energy and power.
To be able to do
Calculate voltages, currents and powers
in simple d.c. and a.c. circuits. (a.c.
circuits will be single-loop only.)
How electrical supplies are provided
both nationally and locally.
Describe the systems in outline and
explain why the arrangements are used
(especially the choice of voltages to
use)
Electrical safety -- earthing, fuses, rcds
Explain how these methods/devices are
used to make electricity safer for the
user.
Electromagnetism -- Bil, Blu and nd/dt
To explain the principles and how they
lead to being able to make motors,
generators and transformers.
Motor selection
To be able to select a type of drive for
simple application situations.
Electronics and "On-off" Control
1. To explain the use of switches and of
AND, OR, NOT logic and to design a
system to meet a reasonably simple
specification.
2. To design, and calculate the gain of,
non-inverting and inverting amplifier
circuits using an operational amplifier.
"Continuous" control
The basic ideas only as per the Week
12 lecture.
The arrangement of the exam
It will be in two sections:
Section A -- Shortish questions testing primarily knowledge of principles and
ability to perform calculations based on them. Examples for practice and to
illustrate the type of question to expect are attached. Section A will carry 70 marks.
Section B -- One longer question which will ask you about the electrical aspects of
a particular product.. You are given the guidance that the product which will be
featured in the January 2002 exam will be an electric lawnmower. Section B will
carry 40 marks. The questions set on the 2001 paper provide a good guide to the
format to expect.
There will be no question choice but it is intended that the total mark out of 110 will
NOT be scaled down in proportion except that a student obtaining more than 100
will be awarded 100 %.
Some Example Section A Questions
A4
A voltage of 5 V is applied across a 5-ohm resistor. Calculate the current
flowing in the resistor and the power dissipated in it.
(5 marks)
A6.
Explain the principle of operation of a transformer. Why is the transformer
one of the main reasons for the almost invariable use of alternating current
rather than direct current in electrical power systems ?
(6 marks)
X
Why it is usual to generate electrical power at typically 11 kV,
transmit it through the National Grid at up to 400 kV and more
locally at 11 kV, but utilise it at 240-415 V.
(8 marks)
A3.
I1
+
5V
--
6 ohm
7 ohm
4 ohm
I3
I2
+
8V
--
(a) Write down three equations from which the values of I1, I2 and I3 could
be calculated. It is not necessary to solve the equations.
(6 marks)
(b) If you knew the value of I1, how would you calculate (a) the power
supplied by the 5-V source and (b) the power dissipated in the 6 -ohm
resistor ?
(4 marks)
Y
An inductance of 0.8 H and a resistance of 120 ohm are connected in
series across the 240-V mains supply. Calculate the circuit current and
power.
Z
Explain
(i) What is meant by a 3-phase a.c. supply (a sketched graph should help !)
(ii) Why a 3-phase power supply is better than a single-phase one both for
the electrical supply industry and for industrial electricity users.
G
We want to control the door lock on a washing machine so that the door
cannot be inadvertently opened whilst the machine is operating. The door lock is
released by a current (or Logic 1 level). It must only be released in the following
circumstances:
1. An engineer's switch is operated (logic 1 or switch closed)
OR BOTH the following apply :
2. There is no water in the drum (A switch or logic 1 indicates the PRESENCE of
water)
3. The machine on-off switch is at OFF (logic 0 or switch)
Use (a) switches and (b) AND, OR and NOT gates.
In Part (a), you must say whether the switches need to be normally-open or
normally-closed.
What electrical "gadget" is likely to be used to operate the lock ? Will the output of
a logic system provide enough current ? If not, how can it be operated ?
H.
What will be the voltage gain of each of the following circuits (not the same
in each case).
12 K
1k
-
+
+
10 k
2k