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# Investigating a factor affecting the voltage output of a transformer.

Extracts from this document...

Introduction

GCSE Physics Coursework

## Introduction

I shall be investigating a factor affecting the voltage output of a transformer.

In order to do this I shall be measuring the range of voltages that are induced across the secondary coil of the transformer when one factor is varied. To do this as accurately as possible and to obtain a fair test I shall ensure that every other variable factor in the practical remains constant.

Background Theory

Transformers are used industrially to increase the low voltages produced in electricity generation (25 kV) to higher voltages to be transported in the grid electricity supply’s cables (250 kV), and then to decrease these voltages for use in domestic appliances (230 V).

A transformer is a device for changing the voltage of alternating current (a.c.) signals and power supplies. Two coils are wound around an iron core, which is preferably laminated so as to reduce energy loss via eddy currents. Iron is a magnetically soft metal, which thus allows it to easily be magnetised and demagnetised (i.e. it doesn’t retain a permanent magnetic field). Transformers utilise the effect of Electromagnetic Induction.  The alternating voltage in the primary coil creates an alternating current, leading to an alternating magnetic field in the primary coil. The magnetic field lines move back and forth and are cut by the secondary coils, inducing a voltage in them; thus a current flows in the secondary coil.

In a step-up transformer there are more turns on the secondary coil than on the primary; there is a larger voltage in the secondary coil than in the primary (i.e. larger secondary voltage).

In a step-down transformer the primary coil has more turns than the secondary, and so there is a smaller voltage in the secondary coil than in the primary (i.e. smaller secondary voltage).

Variables

Middle

0

3

2.33

0.36

0

4

3.20

0.42

0

5

3.75

0.48

0

6

4.42

0.49

0

7

4.90

0.52

0

8

5.50

0.53

0

9

5.90

0.54

0

10

6.10

0.54

0

11

6.34

0.55

0

12

6.70

0.54

Conditions used in preliminary;

Each coil length 1.5m, and 50 turns

Coils range of distances apart

Conditions for actual experiment;

Each coil length 3m, and 100 turns

Coils 0cm apart

## Prediction

I predict that as I increase the primary voltage, the secondary voltage will also increase, and that the primary and secondary voltages should be directly proportional.

This is because as the primary voltage is increased, so the alternating current in the primary coil also increases. This results in the magnetic field lines changing direction more frequently, and so are cut more times in a given time period by the turns on the secondary coil, increasing the voltage induced, via electromagnetic induction, in a given time. Thus increasing primary voltage increases the secondary voltage.

Yet I can be even more specific. As I will have the same number of turns on the primary and secondary coils, and they will be made with the same wire (i.e. will have same resistance), in these conditions the primary voltage should always equal the secondary voltage (in the circumstances of the transformer being 100% efficient). However due to my preliminary results I know that this is not true; the secondary voltage is less than the primary voltage in the experiment I will undertake due to losses in power, the causes of which I will discuss in my Evaluation and Analysis.

## Results

V1=Primary Voltage

V2=Secondary Voltage

 Nominal Voltage (V) V1 (V) V2 (V) MeanV1 (V) Mean V2 (V) Difference between V1 and V2 (V) 1 0.58 0.58 0.59 0.13 0.13 0.13 0.58 0.13 0.45 2 1.43 1.43 1.41 0.32 0.33 0.32 1.42 0.32 1.10 3 1.96 1.95 1.97 0.42 0.41 0.42 1.95 0.42 1.53 4 2.83 2.82 2.83 0.52 0.51 0.51 2.83 0.51 2.32 5 3.16 3.09 3.22 0.54 0.54 0.54 3.16 0.54 2.62 6 3.96 3.97 3.99 0.60 0.60 0.60 3.97 0.60 3.37 7 4.29 4.32 4.38 0.62 0.61 0.61 4.33 0.61 3.72 8 5.18 5.13 5.17 0.64 0.65 0.64 5.16 0.64 4.52 9 5.35 5.42 5.46 0.65 0.65 0.65 5.41 0.65 4.76 10 5.90 5.86 5.94 0.67 0.66 0.66 5.90 0.66 5.24 11 6.09 6.23 6.21 0.67 0.67 0.67 6.18 0.67 5.51 12 6.44 6.62 6.48 0.67 0.67 0.67 6.51 0.67 5.84

Conditions on day for experiment;

Each coil length 2m, and 70 turns

Coils 0cm apart

As I predicted, the power supply tripped out very quickly towards the upper end of my nominal voltage range; particularly from around 9V onwards. While my results are therefore unlikely to be accurate, I believe they are reliable as I read every voltage after the power supply had been turned on for three seconds.

Suitability

I believe that some aspects of my procedure were suitable to gain good results, whilst others were not.

## Analysis

As can be seen in my results table, increasing the primary voltage increases the secondary voltage. In this way my results support my prediction.

I plotted these results on a graph so that this relationship can be seen more clearly. I then constructed lines to see whether the secondary voltage is directly proportional to the primary voltage, as I predicted.

 Primary Voltage (V) Secondary Voltage (V) 0.50 0.11 1.00 0.22 2.00 0.43 4.00 0.6 0.75 0.16 1.50 0.33 3.00 0.53 6.00 0.67

Conclusion

I have described the reasons why I don’t believe my results are accurate in the Analysis section. By looking at my results graph it is possible to see that V1 is certainly not always directly proportional to V2, as the graph curves instead of being straight. Nevertheless I do believe my results to be reliable on account of the smooth trend their averages have produced, and as no anomalies were obtained. Furthermore the ranges, in which replicates from the same nominal voltage lie, are very small. This is illustrated in the table below:

 Nominal Voltage (V) V1 (V) Range between V1 s (V) V2 (V) Range between V2 s (V) 1 0.58 0.58 0.59 0.01 0.13 0.13 0.13 0.00 2 1.43 1.43 1.41 0.02 0.32 0.33 0.32 0.01 3 1.96 1.95 1.97 0.02 0.42 0.41 0.42 0.01 4 2.83 2.82 2.83 0.01 0.52 0.51 0.51 0.01 5 3.16 3.09 3.22 0.13 0.54 0.54 0.54 0.00 6 3.96 3.97 3.99 0.03 0.60 0.60 0.60 0.00 7 4.29 4.32 4.38 0.09 0.62 0.61 0.61 0.01 8 5.18 5.13 5.17 0.05 0.64 0.65 0.64 0.01 9 5.35 5.42 5.46 0.11 0.65 0.65 0.65 0.00 10 5.90 5.86 5.94 0.08 0.67 0.66 0.66 0.01 11 6.09 6.23 6.21 0.14 0.67 0.67 0.67 0.00 12 6.44 6.62 6.48 0.18 0.67 0.67 0.67 0.00

While the method gave reliable results I do believe it would be possible to improve their accuracy. I have stated earlier in the Evaluation what improvements could be made.

I think that I do have enough evidence to draw a conclusion, yet carrying out more replicates and performing the experimental procedure for a greater number of nominal voltages (e.g. every 0.5V) would improve the reliability of my results and the accuracy of their graph’s best-fit line. I would like to perform the experiment for nominal voltages over 10V to find out whether the graph truly levels off, as my results suggest. The more data I collect the more faith I can have in any conclusions drawn.

To further investigate factors affecting the voltage output of a transformer I should like to experiment by varying the number of coils on the primary, the number of coils on the secondary, the ratio of N1 to N2, the size of the iron core, the metal used for the coil wire and the gap between the primary and secondary coils. With this information I would be able to understand better how a transformer works and is affected by different variable factors. Overall I think the experiment worked well.

This student written piece of work is one of many that can be found in our AS and A Level Fields & Forces section.

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