Add formula to compute electric power (#805)

* Add formula to compute electric power

Electric power is defined as P = U * I (Power equals potential times current)

Author: pgrawehr

UnitsNet.Tests/CustomCode/ElectricCurrentTests.cs

@@ -34,5 +34,12 @@ public void ElectricCurrentTimesElectricResistanceEqualsElectricPotential(float
             ElectricPotential potential = ElectricCurrent.FromAmperes(current) * ElectricResistance.FromOhms(resistance);
             Assert.Equal(expected, potential.Volts);
         }
+
+        [Fact]
+        public void ElectricCurrentMultipliedByElectricPotentialEqualsPower()
+        {
+            Power p = ElectricCurrent.FromAmperes(2) * ElectricPotential.FromVolts(10);
+            Assert.Equal(20, p.Watts);
+        }
     }
 }

UnitsNet.Tests/CustomCode/ElectricPotentialTests.cs

@@ -40,5 +40,12 @@ public void ElectricPotentialDividedByElectricResistanceEqualsElectricCurrent(fl
             ElectricCurrent current = ElectricPotential.FromVolts(potential) / ElectricResistance.FromOhms(resistance);
             Assert.Equal(expected, current.Amperes);
         }
+
+        [Fact]
+        public void ElectricPotentialMultipliedByElectricCurrentEqualsPower()
+        {
+            Power p = ElectricPotential.FromVolts(10) * ElectricCurrent.FromAmperes(2);
+            Assert.Equal(20, p.Watts);
+        }
     }
 }

UnitsNet.Tests/CustomCode/PowerTests.cs

@@ -127,5 +127,19 @@ public void PowerDividedBySpecificEnergyEqualsMassFlow()
             MassFlow massFlow = Power.FromWatts(15.0) / SpecificEnergy.FromJoulesPerKilogram(3);
             Assert.Equal(massFlow, MassFlow.FromKilogramsPerSecond(5));
         }
+
+        [Fact]
+        public void PowerDividedByElectricCurrentEqualsElectricPotential()
+        {
+            ElectricPotential u = Power.FromWatts(10) / ElectricCurrent.FromAmperes(2);
+            Assert.Equal(5, u.Volts);
+        }
+
+        [Fact]
+        public void PowerDividedByElectricPotentialEqualsElectricCurrent()
+        {
+            ElectricCurrent i = Power.FromWatts(20) / ElectricPotential.FromVolts(5);
+            Assert.Equal(4, i.Amperes);
+        }
     }
 }

UnitsNet/CustomCode/Quantities/ElectricCurrent.extra.cs

@@ -11,5 +11,12 @@ public partial struct ElectricCurrent
         {
             return ElectricPotential.FromVolts(resistance.Ohms * current.Amperes);
         }
+
+        /// <summary>Calculate <see cref="Power"/> from <see cref="ElectricPotential"/> multiplied by <see cref="ElectricCurrent"/>.</summary>
+        /// <remarks>Electric power is defined as P = U * I.</remarks>
+        public static Power operator *(ElectricCurrent current, ElectricPotential potential)
+        {
+            return Power.FromWatts(potential.Volts * current.Amperes);
+        }
     }
 }

UnitsNet/CustomCode/Quantities/ElectricPotential.extra.cs

@@ -32,5 +32,12 @@ public AmplitudeRatio ToAmplitudeRatio()
         {
             return ElectricCurrent.FromAmperes(potential.Volts / resistance.Ohms);
         }
+
+        /// <summary>Calculate <see cref="Power"/> from <see cref="ElectricPotential"/> multiplied by <see cref="ElectricCurrent"/>.</summary>
+        /// <remarks>Electric power is defined as P = U * I.</remarks>
+        public static Power operator *(ElectricPotential potential, ElectricCurrent current)
+        {
+            return Power.FromWatts(potential.Volts * current.Amperes);
+        }
     }
 }

UnitsNet/CustomCode/Quantities/Power.extra.cs

@@ -92,5 +92,19 @@ public PowerRatio ToPowerRatio()
         {
             return Area.FromSquareMeters( power.Watts / heatFlux.WattsPerSquareMeter );
         }
+
+        /// <summary>Calculate <see cref="ElectricCurrent"/> from <see cref="Power"/> divided by <see cref="ElectricPotential"/>.</summary>
+        /// <remarks>Electric power is defined as P = U * I, so I = P / U.</remarks>
+        public static ElectricCurrent operator /(Power power, ElectricPotential potential)
+        {
+            return ElectricCurrent.FromAmperes(power.Watts / potential.Volts);
+        }
+
+        /// <summary>Calculate <see cref="ElectricPotential"/> from <see cref="Power"/> divided by <see cref="ElectricCurrent"/>.</summary>
+        /// <remarks>Electric power is defined as P = U * I, so I = P / U.</remarks>
+        public static ElectricPotential operator /(Power power, ElectricCurrent current)
+        {
+            return ElectricPotential.FromVolts(power.Watts / current.Amperes);
+        }
     }
 }