1.1. Extended tier only

Fig. 3.1 shows a model of a wind turbine used to demonstrate the use of wind to generate electricity. The wind is blowing towards the model, as shown.

The mass of air passing through the circular area swept out by the turbine blades each second is 7.5 kg. The energy in the kinetic store of the air that passes through this circular area each second is 240 J.

(i) Calculate the speed of the air. 

speed = ........................................................ [3]

(ii) The moving air drives a generator. State the input power of the air passing through the turbine blades.

input power = ........................................................ [1]

1.2. Extended tier only

The output current of the generator is 2.0 A. The output potential difference (p.d.) of the generator is 11 V.

(i) Calculate the output power of the generator. 

  output power = ........................................................ [2]

(ii) Calculate the efficiency of the wind turbine. 

efficiency = .................................................... % [2]

1.3. The density of air is 1.3 kg / m³.

Calculate the volume of air passing through the circular area swept out by the turbine blades each second.