"End of Chapter Review" Utilization of Internal Energy PPT

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"End of Chapter Review" Utilization of Internal Energy PPT

Part One: Practical High School Entrance Examination

Test point 1: Judgment of the working process and stroke of gasoline engines

(1) A working cycle of a gasoline engine includes four strokes: suction stroke, compression stroke, power stroke, and exhaust stroke. Mechanical energy is converted into internal energy during the compression stroke, and internal energy is converted into mechanical energy during the power stroke. (2) Determine the stroke based on the opening and closing of the valve and the movement of the piston: ① The intake valve opens, the exhaust valve closes, and the piston moves downward, which is the suction stroke; ② The intake valve closes, the exhaust valve opens, and the piston moves upward The movement is the exhaust stroke; ③ both valves are closed, the piston moves upward, which is the compression stroke; ④ both valves are closed, the piston moves downward, and the spark plug ignites at the same time, which is the power stroke.

Example 1 [Taizhou High School Entrance Examination]The gasoline engine is a type of heat engine. When gasoline is burned in the cylinder, it converts ______ energy into _____ energy. Figure 14-Z-1 shows a schematic diagram of the working status of a four-stroke gasoline engine. It can be seen from the figure that it is in the _____ stroke at this time.

Test point 2 Calculation of calorific value and heat of fuel

(1) The calorific value is a characteristic of the fuel itself. It is only related to the type of fuel and has nothing to do with the shape, quality, volume, complete combustion, or amount of heat released by the fuel. (2) The formula for the heat released by fuel combustion: Q releases = qm; variant: m = Q releases q, q = Q releases m. (3) Calculation formula of heat engine efficiency: η = W useful Q discharge; variant form: W useful = η Q discharge, Q discharge = W useful η. (4) The efficiency of a heat engine cannot reach 100%; the main way to improve the efficiency of a heat engine is to increase the utilization rate of fuel.

Example 2 - Liuzhou High School Entrance Examination 4.2×103 J/(kg·℃), assuming that the heat released is completely absorbed by water] ()

A. 2 kgB. 20kg

C. 50kg　D． 500kg

Example 3 [Jingzhou High School Entrance Examination] During the wheat harvest season every year, farmers often pile wheat straw in the fields and burn it, which not only pollutes the environment but also wastes resources. According to calculations, 1 t of wheat straw can produce 270 m3 of biogas in a biogas digester, and the remaining residue is still high-quality organic fertilizer. Statistics show that a village in Jingzhou City can generally produce 500 tons of wheat straw every year. If these wheat straws are used to generate biogas in a biogas digester, the generated biogas can release _________J heat after complete combustion; under standard atmospheric pressure, these wheat straws The amount of heat can boil a __________ kettle containing water with a mass of 2.5 kg and an initial temperature of 20°C. [The calorific value of biogas is 1.9×107 J/m3, and the specific heat capacity of water is 4.2×103 J/(kg·℃)]

Test Point 3: Transformation and Conservation of Energy

(1) Various phenomena in nature are interconnected, and under certain conditions, various forms of energy can be transformed into each other.

(2) Before and after the change, if the form of energy does not change, it is classified as energy transfer; if the form of energy changes, it is classified as energy transformation.

(3) Energy will neither be destroyed nor created out of thin air. It will only be converted from one form to other forms, or transferred from one object to other objects. In the process of transformation and transfer, the total amount of energy constant.

(4) All energy conversion processes obey the law of conservation of energy.

Review PPT at the end of the chapter, part 2: Entering the majors and high schools

Advantage 1: The working process of gasoline engines and the efficiency of heat engines

The working process of a gasoline engine covers knowledge such as speed, inertia, pressure, pressure, mechanical work and power, combustion heat of fuel, energy conversion, heat engine efficiency, etc. It is a hot topic in the high school entrance examination and can appear in various forms of comprehensive questions. The more difficult part is to solve the work caused by gas pressure during the power stroke, which requires students to not only understand the operating conditions of the piston in the cylinder, but also accurately use the formula W=Fs to calculate the amount of work.

Typical example 1 (Extended material questions) Read the passage and answer the questions.

car engine

The engine is the power source of the car. The gasoline engine uses gasoline as fuel to make the piston reciprocate in the cylinder. A working cycle goes through four strokes: suction, compression, power and exhaust. The performance of the gasoline engine is related to the cylinder displacement. Cylinder displacement refers to the volume that the piston passes through the cylinder in one stroke. It depends on the area of ​​the piston and the distance the piston moves up and down (stroke length). If the engine has several cylinders, the sum of the "working volumes" of all cylinders is called the engine displacement. In fact, cars often use multi-cylinder engines.

As shown in Figure 14-Z-3, the engine has four cylinders (labeled 1, 2, 3, and 4 in the figure), and the pistons of the four cylinders are connected to a crankshaft through connecting rods. The work process of each cylinder is staggered. In each half cycle of the flywheel rotation, one cylinder is doing work, and the other three cylinders are in the suction, compression and exhaust strokes respectively.

(1) When a gasoline engine works, it converts the internal energy obtained from fuel combustion into ________ energy.

(2) If the displacement of a cylinder is V and the average pressure of the gas on the piston is p, then the work done by the gas on the piston during a power stroke is ________ (expressed by letters).

(3) If the car engine outputs constant power and slows down when climbing a hill, the purpose is to ____________.

(4) In a four-cylinder engine, cylinder No. 1 is in the power stroke, and cylinder No. 4 is in the stroke ________. (fill in the serial number)

A. Inhale B. Compression C. Doing work D. exhaust

Typical Example 2 (Final Question of High School Entrance Examination) [Shaanxi High School Entrance Examination] A certain gasoline-electric hybrid car has the characteristics of fuel economy and high energy utilization. The relevant information is as follows. In a certain horizontal road test, the car traveled 170 kilometers at a medium speed and a constant speed, consuming a total of 10 L of gasoline. During the test, the internal combustion engine not only provides energy to the wheels, but also charges the battery. At the same time, the battery transfers part of the energy to the wheels through the electric motor. At this time, the internal combustion engine and the electric motor jointly drive the vehicle forward. Afterwards, the staff conducted a braking test and drew an image of the relationship between the braking distance (the distance from the start of braking to the stop of the car) and the speed during braking, as shown in Figure 14-Z-4.

(1) It can be seen from the image that the higher the vehicle speed, the longer the braking distance.

(2) What is the pressure on the horizontal ground when the car is stationary without load? (g is taken as 10 N/kg)

(3) In a constant speed driving test on a level road, if the average resistance is 1000 N, how much work is done by the traction force?

(4) In the test of driving at a medium speed and constant speed on a level road, if the efficiency of the car's internal combustion engine is 53%, how much energy does this process ultimately add to the battery? (Ignore the heat loss of the battery and electric motor, ρ gasoline is 0.7×103 kg/m3, q gasoline = 4.6×107 J/kg)

Advantage 2: Law of Conservation of Energy

Using energy conversion to analyze physical phenomena is another way to explore physical phenomena and their laws, and is an important content to further study in the future. To solve such problems at the junior high school level, students are required to master the concept of energy, common energy and its influencing factors, the law of conservation of energy, calculation of work, etc. In particular, they must know that the conversion between different forms of energy is through work. to achieve.

Typical example 3 (open inquiry question) [Wenzhou High School Entrance Examination] According to the law of conservation of energy, under the condition that there is no heat transfer with the outside world, the increase in the internal energy of an object is equal to the amount of work done by the outside world on the object. In order to verify this rule, an interest group designed an experiment as shown in Figure 14-Z-5: A certain mass of water is placed in the container, a rotating shaft with blades is installed in the middle, a rope is wound around the rotating shaft, and the other end of the rope is passed through The pulley is connected to a heavy object; when the heavy object drops, the rope pulls the shaft to rotate, driving the blades to rotate, causing the temperature of the water in the container to rise. Combined with the specific heat capacity of the water, the increased internal energy of the water is calculated to verify the increase in the internal energy of the water. Is the work done by the weight of the heavy object equal to that of the weight?

(1) In order to complete this experiment, in addition to the electronic balance for measuring mass, the measuring tools also required are _______________.

(2) The interest group discovered during the experiment that the increase in the internal energy of water is less than the work done by the heavy object. Please write down one reason for this phenomenon ____________________________.

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For more information about the "Utilization of Internal Energy End of Chapter Review" PPT courseware, please click the "Utilization of Internal Energy ppt End of Chapter Review ppt" tag.

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