You are tasked to use appropriate data sheets/sources to obtain relevant information for use in various calculations.
You are required to make appropriate judgement on the level of detail required and the presentation of the results in the most suitable format.
Task 1
In the DC circuit shown above, apply Kirchoff's laws to calculate the current in each branch.
Be able to apply DC theory to solve electrical and electronic engineering problems.
Solve problems using Kirchoff's laws to calculate currents and voltages in circuits.
Pass: Apply the stated law correctly to the given circuit to enable the calculation of currents and give your answers in a neat and logical manner, referring to the diagram and/or your own sketches and using appropriate units.
Task 2
In the DC circuit shown above, apply Thevenin's theorem or Kirchoff's loop current theory to calculate the current in and the voltage across the 25 Ω resistor.
Be able to apply DC theory to solve electrical and electronic engineering problems.
Solve problems using circuit theorems to calculate currents and voltages in circuits.
Identify and apply strategies to find appropriate solutions. Effective judgements have been made.
Pass: Apply one of the stated laws correctly to the given circuit to enable the calculation of current and voltage, and give your answers in a neat and logical manner, referring to the diagram and/or your own sketches and using appropriate units.
With either theory, you should justify your judgement of how to simplify or equate the circuit to enable efficient calculation of the required information.
Task 3
For the series RC circuit shown above, where there is no initial charge across the capacitor, on closing the switch, 'S', determine:
(a) the initial value of the current,
(b) the time constant of the circuit,
(c) the current's value after 1 second from switching on,
(d) the voltage across the capacitor after 1.3 seconds from switch on,
(e) the time from switch on when the resistor voltage was 32 V.
Be able to apply DC theory to solve electrical and electronic engineering problems.
Solve problems involving current growth/decay in L-R circuits and voltage growth/decay in C-R circuits.
Task 4
From the series RL circuit shown above, where there is no initial voltage across the inductor, on closing the switch, determine:
(a) the steady-state value of the current flowing in the circuit,
(b) the time constant of the circuit,
(c) the induced voltage after 0.08 seconds,
(d) the time taken for the current to rise to 75% of its final value,
(e) the value of the current after 0.25 seconds.
Be able to apply DC theory to solve electrical and electronic engineering problems.
Solve problems involving current growth/decay in L-R circuits and voltage growth/decay in C-R circuits.
Select/design and apply appropriate methods/ techniques. 2.1 Relevant theories and techniques have been applied.
Pass: All parts need to be attempted, with solutions given to a good degree of accuracy, in a logical manner and using suitable units.
You have chosen and correctly applied a technique which allows efficient calculations to be completed.
Task 5
A resistor of 45Ω is in series with a pure inductor of 105.3 mH. This circuit is connected across a 100 V rms, 100 Hz voltage supply. Determine:
(a) the inductive reactance,
(b) the circuit impedance,
(c) the current flowing,
(d) the potential difference across the resistor,
(e) the potential difference across the inductor,
(f) the phase angle between the supply voltage and current.
All the circuit components remain unchanged but a 25 μF capacitor is placed in series with the resistor and pure inductor. Find:
(g) the current flowing,
(h) the voltage across the resistor,
(I) the voltage across the coil,
(j) the voltage across the capacitor,
(k) the phase angle between the supply voltage and current.
Be able to apply single phase AC theory to solve electrical and electronic engineering problems.
Apply AC theory to solve problems on R, L, C circuits and components.
Demonstrate convergent/lateral/creative thinking. Problems have been solved.
Pass: Parts (a) to (f) have been attempted, with solutions given to a good degree of accuracy, in a logical manner and using suitable units.
Parts (a) to (f) have been solved correctly and additionally, parts (g) to (k) have been solved, with all solutions given to a good degree of accuracy, in a logical manner and using suitable units.
Task 6
An electric motor has an output power of 5.75 kW and an efficiency of 85%. It has a power factor of 0.725 lagging when operated from a 230 V, 50 Hz supply.
It is required to improve the power factor to 0.925 by connecting a capacitor in parallel with the motor. Determine:
(a) The current taken by the motor,
(b) the supply current with the power factor correction,
(c) the current taken by the capacitor,
(d) the capacitance of the capacitor,
(e) the kvar rating of the capacitor.
Be able to apply single phase AC theory to solve electrical and electronic engineering problems.
Apply AC theory to solve problems on R, L, C circuits and components.
Task 7
(a) Explain when a sinusoidal electrical waveform conducted through a pn junction diode to a resistive load, does not appear sinusoidal across the resistor.
(b) Draw a circuit diagram and also show the waveforms from source and across the load.
(c) A complex voltage waveform is composed of harmonics and is described by the following expression:
v = 200sin(ωt + Π/6) + 150sin(2ωt - Π/3) + 75sin(3ωt + Π/5).V
is applied to the following circuits comprising of pure components of:
i) 25 Ω resistor,
ii) 25 x 10-3 H inductor,
iii) 25 x 10-6 F capacitor.
The fundamental frequency is 500 Hz. Determine the current expression flowing in each separate circuit.
Be able to apply single phase AC theory to solve electrical and electronic engineering problems.
Recognise a variety of complex waveforms and explain how they are produced from sinusoidal waveforms.
Pass: All parts have been attempted, with solutions (explanations, diagrams and expression) given using suitable supporting information and justifications.
Task 8
A 10 kVA on full-load single phase transformer has a turns ratio of 25:1 and is fed from a 5.0 kV supply.
Neglecting losses (i.e. assuming the ideal transformer) determine:
(a) the full-load secondary current,
(b) the minimum load resistance which can be connected across the secondary windings for full-load,
(c) the primary current at full-load,
(d) the input impedance seen at the primary windings,
(e) the power dissipated across the load resistance.
Be able to apply single phase AC theory to solve electrical and electronic engineering problems.
Apply AC theory to solve problems involving transformers.