Q5. A student investigated how the output voltage of a model wind turbine was affected by the number of turbine blades.

The equipment he used is shown in the diagram below.

 

(a) Suggest two factors, other than the number of turbine blades, that will affect the output voltage of the model wind turbine.

Wind strength - the speed of the airflow from the hairdryer - power setting on the hairdrier. The distance between the hairdrier and the turbine will also affect this.

The area of turbine being hit by the airflow - length / area / size / shape/ angle of incidence of the turbine blades

In questions like this you have to be careful not to give two factors that the examiner considers to be both relating to the same point.... for example distance of hairdrier from the turbine and power of the hairdrier would only give you one mark!

- Personally I think this is unfair - but I don't make the rules!

[2 marks]

(b) Some of the student's results are shown in the graph below.

(i) Plot the remaining results on the graph using the data in this table.

Number of turbine blades	Output voltage in volts
5	0.39
7	0.50
8	0.56

All three correct gives two marks - any one point incorrectly plotted lose one mark - two mistakes you get no marks.

[2 marks]

(ii) The output voltage for 6 turbine blades is lower than expected. The low value was caused by a measurement error. State the name of this type of measurement error.

Random error

[1 mark]

(iii) What two conclusions can be made from the student's results as the number of blades is increased from 1 to 4?

There is zero output voltage (or speed) with 1 blade but, as the number of blades increases, output voltage (or speed of rotation) increases.

Note it is not a directly proportional relationship.... that would need the graph to be a straight line through the origin.

[2 marks]

(c) Commercial wind turbines can be manufactured with a number of blades between 2 and 8. Suggest two factors that manufacturers would need to consider when designing and constructing commercial wind turbines.

Any two from:

• output voltage / power (required)
• mass / weight / material / area / size / shape / length of blades
• height / position / location of turbine
• cost to construct turbine or reference to 'payback time'
• environmental impact of wind turbine - for example reference to noise / visual pollution

Again, you have to be careful not to give two factors that the examiner considers to be both relating to the same point.... for example noise from the turbine and visual pollution would only give you one mark!

[2 marks max]

(Total 9 marks)