Important sections are missing from 'Planning A' and 'Planning B', and from the Data analysis and Evaluation. Top marks have been scarificed in the effort to be brief.
The transformer, shown actual size, is made from hand wound 22 gauge copper wire on ferrite cores salvaged from an old TV line output transformer.
The research question arises out of a knowledge of standard soft iron cored transformers. The introduction should include a brief mention of transformer operation, the standard design, (with a photograph) and the way(s) in which this particular transformer differs. Without this explanation the research question stands alone without rationale.
Research questions
What is the efficiency of this hand-wound ferrite core transformer and is the efficiency dependent on the input power.
Hypothesis
The efficiency will be close to 1.
Commercial transformers have efficiencies of at least 95%. This transformer is closely wound and the core is large and strongly ferromagnetic. Most of the field of the primary will thread the secondary and the coils become only slightly warm during operation. The efficiency is therefore expected to be at least 80%.
There are two research questions and only one hypothesis.
Procedure
A small light bulb was used as a load and an AC power supply with four fixed output voltages from 2 - 12 volts was selected.
AC meters of appropriate ranges were needed. The Department has sets of moving coil AC meters in the 0-15 Volt range and current meters in the1-5 Amp range. The current meters will not read accurately from 0-1 Amps. A digital meter with a 0-200 milliamp AC range was selected. Only one digital meter was available.
Both meters were placed first on one side and then the other. The meters are not ideal, but any errors introduced will be very small because the power supply has fixed ranges.
The connections are made with crocodile clips. The wires were cleaned with sand paper to reduce any errors due to poor contacts.
Appropriate meters were selected but the procedure section is vague and difficult for a general reader to follow. A circuit diagrams showing the meter positions would be more helpful here, than it is in the Data collection section below.
Data
The circuit is shown (upper diagram). Input and output voltages and currents are listed in Table 1.
Reliable data is clearly listed wih errors.
Analysis
The power input and output, V1I1 and V2I2, respectively were calculated and are plotted with errors in Graph 1.
The graph is well plotted with errors but there is no sample calculation and no table to accompany the graph.
If the transformer were 100 % efficient the data points would lie on the straight line with slope 1 shown on Graph 1. Clearly the efficiency is about 50% and is not constant as a function of input power, since the data points lie very much below the line, and are not themselves on a straight line.
Plotting the efficiency ...
... against input power (Graph 2) shows that, within errors, the transformer is most efficient for input power in the 400 milliwatt region.
Graph 2 is well plotted but again there is no sample calculation, no table and also no explanation of how the line was fitted.
Evaluation
The selected meters were appropriate and the bulb was a suitable load. Variations in the resistance of the filament would not affect the power values. Since the power supply had fixed settings it was not necessary to measure input and output power at the same times. It would be interesting to compare the relatively low efficiency of this transformer with a commercial transformer wound on m metal rather than ferrite. The lowered efficiency at large power inputs could be accounted for if the ferrite was saturating. No satisfactory explanation can be offered for the reduced efficiency at very low power inputs.
The evaluation is incomplete in two respects.
1 There is no detailed discussion of the graphs and what they mean.
2 There is not enough discussion of possible reasons for the shape of the final graph or of ways to test the magnetic properties of the ferrite.