Efficiency shows the attitude of useful work which is performed by the mechanism or the device, to spent. Often take amount of energy which consumes the device to perform work for the spent work.
It is required to you
- - car;
- - thermometer;
- - calculator.
Instruction
1. To calculate the efficiency (E) divide useful work of Ap into work the spent Az, and result increase by 100% (efficiency = Ap/Az100 of %). Receive result as a percentage.
2. When calculating efficiency thermalof engine, useful work consider the mechanical work performed by the mechanism. Take the amount of heat allocated by the burned-down fuel which is a power source for the engine for the spent work.
3. Example. The average force of draft of the engine of the car is 882 N. On 100 km of a way it consumes 7 kg of gasoline. Determine the efficiency of its engine. At first find a useful job. It is equal to the work of force of F on S distance overcome by a body under its influence by Ap of =F∙S. Determine the amount of heat which will be allocated when burning 7 kg of gasoline, it also will be the spent work of Az =Q=q∙m where q is the specific heat of combustion of fuel, for gasoline it is equal 42∙10^6 to J/kg, and m is the mass of this fuel. Efficiency of the engine will be equal to efficiency = (F∙S) / (q∙m) of ∙100% = (882∙100000) / (42∙10^6∙7) 100%=30%.
4. Generally to find efficiency, any thermal machine (the internal combustion engine, the steam engine, the turbine, etc.) where work is performed by gas, has the efficiency equal to the difference of the warmth given by the Q1 heater and received by the Q2 fridge find the difference of warmth of the heater and fridge, and divide into warmth of the efficiency heater = (Q1-Q2)/Q1. Here efficiency is measured in submultiple units from 0 to 1 to transfer result to percent, increase it by 100.
5. To receive the efficiency of the ideal thermal car (cars Carnot), find the relation of a difference of temperatures of the T1 heater and T2 fridge to temperature of the KPD=(T1-T2)/T1 heater. It is extremely possible efficiency for concrete type of the thermal car with the set temperatures of the heater and fridge.
6. For the electric motor find the spent job as the work of power for the period of its performance. For example, if the electric motor of the crane with a power of 3.2 kW lifts cargo weighing 800 kg on height of 3.6 m for 10 with, then its efficiency is equal to the relation of useful work of Ap of =m∙g∙h where m is the mass of cargo, to m/s g≈10² the acceleration of gravity, h there is height on which lifted cargo, and the spent work of Az = Pt where P – engine capacity, t – time of its work. Receive a formula for determination of efficiency = Ap/Az100%= (m∙g∙h) / (Pt) ∙100%= %= (800∙10∙3,6) / (3200∙10) 100%=90%.