 Since we have been talking about the multi-stage machines where each stage consists of a stator followed by a rotor, the degree of reaction of a stage may be defined more or less in the same manner as for a rotor. So the degree of reaction of a stage is defined as the enthalpy change, static enthalpy change across the rotor divided by the stagnation enthalpy change across the entire stage consisting of a stator and a rotor. Since there is no work interaction in a stator, H02 equal to H01, so this expression may be written as H2 minus H3, the static enthalpy change across the rotor divided by the stagnation enthalpy change across the stage or equivalently at the rotor itself. So it's almost identical to the expression that we wrote down. The degree of reaction for a rotor as we mentioned earlier usually varies between 0 and 1. In the case of a stage, the degree of reaction can actually be negative in some cases if the design is very poor or it can actually be again more than 1 in the case of a stage. So we will not go into these two extreme situations. So we will look at this degree of reaction of a stage almost in the same manner as that of a rotor itself. The only difference is that 1 refers to the inlet of the stator, 2 refers to the exit of the stator or rotor inlet and 3 refers to rotor exit, which would also be the inlet to the following stator that is the notation that we will use. Let us look at a couple of examples to illustrate how we calculate the degree of reaction for a stage. The first example reads like this. In an axial turbine, the rotor and stator blades of the same shape that are reversed in direction show that the degree of reaction of the stage is 40%. So let us just quickly go back and take a look at the blade shape here using the notation that we have just given. So let us look at the turbine stage here. So here is 1, 2 and 3. So the blade shapes are the same, but they are reversed in direction is the information that is given, which means that alpha 2, which is the flow angle at the exit of the stator should be equal to the blade angle at the exit of the rotor. So alpha 2 is equal to beta 3 and alpha 1, which is the flow angle at entry to the rotor is also equal to alpha 3 because that is the same angle at which the flow enters the stator in the following stage, so alpha 1 equal to alpha 3 and which in turn is equal to the blade angle at entry to the rotor, so that means alpha 1 equal to alpha 3 equal to beta 2. So to summarize alpha 2 equal to beta 3 and alpha 1 equal to alpha 3 equal to beta 2 is what we will have if the blades are symmetric for just reversed in direction. So that is what we have written here, alpha 2 equal to beta 3 and alpha 1 equal to alpha 3 equal to beta 2. Now if you construct a velocity triangle with this information for an axial rotor it should be very easy to show that C2 is equal to V3 and C3 equal to V2 in this case, I urge the student to actually go through this construction and convince themselves of this fact. Therefore the enthalpy change across the rotor H2 minus H3 is C3 square minus C2 square over 2 since H plus C square over 2 is constant for an axial machine and if we substitute for the relative velocity from here we get this to be equal to V2 square minus V3 square over 2. Now the change in stagnation enthalpy across the rotor H02 minus H03 is nothing but the specific work and we may write it like this using Euler turbine equation and after setting U2 equal to U3 because it is an axial machine. If we substitute again for the relative velocities from here we get the change in specific stagnation enthalpy to be equal to V2 square minus V3 square. So the degree of reaction which is defined as H2 minus H3 divided by H02 minus H03 then comes out to be identically equal to 1 half.