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HEAT ENGINE - 10th Science Notes and Question Bank



Text Book Question and Answers

Four alternatives are gives to each of the incomplete statements/questions. Choose the correct answer.

1. The energy transformation in a heat engine is,

(a) Mechanical into heat. (b) Heat into mechanical.

(c) Mechanical into potential (d) mechanical into chemical

Answer: (b) Heat into mechanical

2. Forward movement of a piston in steam engine is called.

(a) Expansion stroke (b) exhaust stroke (c) intake stroke (d) ignition stroke

Answer: (a) expansion stroke

3. In a steam engine the steam cylinder is connected to the condenser by, (a) piston (b) crankshaft (c) outlet valve (d) inlet valve

Answer: (c) outlet valve

4. Both the valve of a petrol engine is closed during.

(a) Intake stroke (b) exhaust stoke (c) compression stroke (d) fuel intake stroke

Answer: (c) compression stroke

5. An engine is designed to convert 20% of heat energy into work. If the steam in the engine has 80 K J of heat energy, the useful work done by the engine is,

(a) 16 K J (b) 100 K J (c) 40 K J (d) 50 K J

Answer: (a) 16 K J

6. If a temporary forest camp, the best way to generate electricity for several hours is, to use the following engine.

(a) Steam engine (b) petrol engine (c) hand operated dynamo (d) diesel engine

Answer: (d) diesel engine

Fill in the blanks:

1. The part of a petrol engine in which petrol vapour and air are mixed is carburettor

2. Linear movement of the piston in a heat engine is converted into circular motion by Crank shaft

3. The stroke of a heat engine in which outlet valve opens is Exhaust stroke

4. Internal combustion engine that does not use spark plug is called Diesel engine

5. The fuel used in Raichur thermal power plant is Coal

Answer the following questions

1. An engine is 40% efficient. What is the meaning of this statement?

It means 100 units of heat is supplied to an engine, 40 units of heat energy is converted to useful mechanical work.

2. Make a list of the differences between petrol engine and diesel engine

Petrol engine

Diesel engine

Petrol engine are spark ignition engines. Require spark plug.

Diesel engines are compression ignition engines. Spark plug is not required.

Petrol vapour is used as fuel.

Micells of diesel are used as fuel

The cost of petrol is comparatively high.

The coast of diesel is comparatively less.

Expansion of gaseous products with pressure impulse.

Expansion against constant pressure

Efficiency is comparatively less.

Efficiency is comparatively more.

Emits less smoke

Emits more smoke

In the intake stroke fuel air mixture enters the cylinder

In the intake stroke only air enters the cylinder

3. Make a list of the limitations of a steam engine.

a) It is bulky, hence connote be used to run small machines.

b) It cannot be started immediately

c) Its efficiency is less

d) There is risk of accident due to bursting of boiler.

4. Explain the intake stroke of a petrol engine.

The vapourised mixture of petrol and air is let in through the inlet valve. The outlet valve remains closed. Piston moves away from the spark plug.

5. Diesel engines do not require spark plug. Why?

The compression ratio of air is to fuel in the diesel engine 4:1 to 25:1, as compared to petrol engine of 4:1 to 10:1, as result of compression, high temperature around 1000k is produced inside the engine igniting the fuel air mixture, and hence a spark plug is not required.

6. Draw a neat diagram of expansion stroke of a steam engine


7. Draw a neat diagram of petrol engine and label the parts.


8. An engine is designed to convert 40% of heat energy into work. If the heat energy consumed by the engine is 60 K J, how high would this engine lift an object of mass one kilogram from the ground?(Assume g=10ms-1, W=mgh)


9. Ever increasing number of internal combustion engine vehicles is one of the causes of air pollution. How can it be controlled? What are the alternatives? Write an essay of about half a page on this.

Internal combustion engine such as reciprocating internal combustion engines produce air pollution emissions, due to incomplete combustion of carbonaceous fuel, the man derivatives of the process are carbon dioxide, water and some root are called particulate matter some additional products of the combustion process that include nitrogen oxides and sulphur and some un combusted hydrocarbons depending on the operating conditions and fuel air ratio, incomplete combustion also leads to the production of carbon monoxide. Further chemicals released are benzene butadiene’s that are also hazardous air pollutants.

To know this emission tests should be conducted often and the engines should be served regularly

The alternatives are CNG, natural gas and LPG can be used instead of petrol and diesel.

10. If non-renewable sources such as petrol and diesel, get depleted over a period of time, how to run heat engines? Write an essay on this in about half a page.

A non-renewable resource is a resource that does not renew its self at sufficient rate for sustainable economic activity, original organic materials with the aid of heat and pressure becomes fuel sources such as oil or gas over a period of time. Fossil fuels such as coal petroleum and natural gas are all non-renewable resources.

Run heat engine by using metal ores and other non-renewable resources. The metals themselves are present is vast amount in the earth’s crust and are continuing concentrated and replenished over millions of years.

Metal ores as a whole are is in exhaustible because the amount vastly exceeds human demand on all time frames, though they are technically non-renewable just like with rocks and sand, humans could never deplete the world’s supply; in this way metal ores are considered vastly greater in supply to fossil fuels because metal ores are formed in the earth crust


Additional Question and Answers

1. Name the various effects of heat.

When heat is added to a substance, the following effects can occur:

a) change of physical state of the substance

b) increase in temperature

c) increase in the volume (expansion)

d) chemical change

e) Change in the shape of the substance.

2. What property of heat is used in the making of heat engines?

The transition of a substance from liquid state to vapour state through the application of heat brings about an enormous increase in the volume of the substance. This property of heat is used in the making of neat engines,

3. Explain the basis of working of a steam engine.

In a steam engine, water is heated to produce steam. The volume of steam so produced is far higher than the volume of water. Thus, steam exerts tremendous pressure. This pressure is used to do mechanical work.

4. Which are the two types of movement found in a gaseous (vapour) system? Which one of these movements is used to run heat engines?

The two types of movements found in a gaseous system are:

1) The random motion of the molecules within the system

2) The broad motion of the gaseous matter along the direction of flow.

The broad motion of the gaseous matter is used to run heat engines

5. What is the significance of the invention of the steam engine?

The invention of steam engine helped to bring about industrial revolution.

6. What is a steam engine?

An external combustion engine which uses the energy contained in the expanding steam to do mechanical work is called a steam engine

7. The main components of an external combustion engine. Mention the function of each.

The following are the major components of an external combustion engine:

i) Boiler; Produces and stores steam at high pressure.

ii) Inlet valve: Allows steam from the boiler to enter into the cylinder and not in the opposite direction.

iii) Cylinder: It is the main part of the engine where the expanding steam does the work.

iv) Piston: It is the part of the engine on which mechanical work is done by the expanding steam.

v) Connecting rod: It transfers the motion of the piston on to the crank system.

vi) Crankshaft: It converts the linear motion of the piston into rotatory motion.

vii) Outlet valve: Allows the spent steam to move out of the cylinder into the condenser.

viii) Condenser: Collects the spent steam and condenses it.

ix) Pump: It transfers the contents of the condenser to the boiler.

8. What are the advantages of internal combustion engine over external combustion engine?

a) The efficiency of an internal combustion engine is greater than that of an external combustion engine.

b) It can be started instantaneously

c) Internal combustion engine can be manufactured in a range of size. They can be fitted to small machines.

d) There is no risk of accident due to the storage of material at high pressure.

9. Give two examples for an internal combustion engine.

1. Petrol engine 2. Diesel engine.

10. Give an example for external combustion engine.

Steam Engine.

11. What is the main difference between external and internal combustion engines?

a) In an external combustion engine, fuel burns outside the engine. b) In an internal combustion engine, fuel burns inside the engine.

12. What is a heat engine?

Heat engine is a device which converts heat into useful mechanical energy.

13. Name the two types of heat engines.

A) External combustion engine B) Internal combustion engine.

14. Explain the basic principle of a heat engine.

Heat engines work on the principle of the law of conservation of energy. The law of conservation of energy states that ‘energy is neither created nor destroyed but can be converted from one form into another in a heat engine the heat energy is converted into mechanical energy.

15. Draw a neat diagram of exhaust stroke of a steam engine


16. Explain with a sketch the working of a steam engine


A typical steam engine consists of a cylinder fitted with an airtight piston. The piston is connected to a crankshaft by means of a connecting rod. A boiler is connected to the cylinder through a valve called inlet valve. Cylinder is also connected to a condenser through another valve called outlet valve. The condenser is connected to the boiler through a pump. The water in the boiler is heated to generate steam which gets stored at high pressure. The steam under high pressure gets into the cylinder through the inlet valve. The expanding steam forces the piston to move outwards. This stroke is called expansion stroke. During the caparison stroke the outlet valve remains closed. At the end of the stroke the inlet valve gets closed. As the piston moves inwards the outlet valve opens. The spent steam in the cylinder is pushed into the condenser. The cycle repeats.

17. Describe with neat sketches the four strokes of a petrol engine.

(1) Intake stroke: The piston moves outwards away from the cylinder head. This results in low pressure inside the cylinder and the inlet valve opens. The fuel mixture from the carburettor enters the cylinder. The outlet valve remains closed.


(2) Compression stroke: Both the inlet and outlet valves are closed and the mixture is compressed by the piston moving towards head


(3) Power stroke: The compressed mixture is ignited by the spark produced by the spark plug. A lot of heat is released. The product of combustion consisting of carbon dioxide and water vapours expands suddenly. The piston is pushed outwards with the great force


4) Exhaust stroke: The exhaust valve opens. The piston moves back. The waste gases are pushed out of the cylinder through the exhaust valve


The above cycle is repeated. Piston moves to and fro quickly. The movement of the piston pushes the crankshaft and makes it rotate rapidly.

18. Mention the major components of a petrol engine. State the function of each.

Inlet valve: Allows the fuel mixture from the carburettor to enter into the cylinder.

Cylinder: It is the main part of the engine where the expanding gaseous products produced by burning the fuel do work.

Piston: It is the part of the engine on which mechanical work is done by the expanding gases. Connecting rod: It transfers the motion of the piston on to the crank system.

Crankshaft: It converts the linear motion of the piston into rotatory motion.

Outlet valve: Allows the exhaust gases to move out of the cylinder into the surrounding medium. Spark plug: Produces sparks at regular intervals to ignite the fuel mixture.

19. What are the limitations of a petrol engine?

Petrol engines are used in lightweight vehicles like cars, scooters and motorcycles. The cost of petrol is very high when compared to that of fuels like diesel oil. The continuous supply of petrol also results in the wastage of small quantity of petrol, as a part of the petrol does not undergo combustion completely.

20. Who invented 1.Petrol engine 2. Diesel engine

Petrol engine: Nicholas Otto.

Diesel engine: Rudolph diesel.

21. What are the functions of the following in a petrol engine?

(a)inlet valve. (b) Outlet valve. (c)Spark plug (d) Carburettor (c) Crank Shaft.

(a) Inlet valve: Inlet valve allows the fuel air mixture into the cylinder.

(b) Outlet valve: Outlet valve allows the exhaust gases to escape.

(c) Spark plug: Spark plug produced spark to ignite the fuel air mixture.

(d) Carburettor: Carburettor mixes petrol and air in proper proportions

(e) Crank Shaft: Crank Shaft converts linear motion of the piston into circular motion

22. Write the difference between internal and external combustion engine

Internal combustion engine

External combustion engine

1. Efficiency is greater than external combustion engine.

2. It can started instantly

3. Fuel is burnt inside the cylinder

4. There is no risk

5. It can be fitted in small machines also.

1. Efficiency is low

2. It cannot be started instantly

3. Fuel burnt outside the cylinder

4. Risk involved is very high

5. It can be fitted only in big machines.

23. Explain the working of diesel engine.

The construction of a diesel engine is similar to that of a petrol engine except that fuel injunction pump is fitted in place of the spark plug. A carburettor is not required in a diesel engine. The working cycle of a diesel engine also consists of the four strokes - intake, compression, power and exhaust strokes. During the intake, filtered air is taken into the cylinder and compressed during the compression stroke. The compression generates enough heat to ignite the fuel. At the end of compression stroke requisite amount of diesel is injected into the cylinder. Diesel bursts into flame instantaneously. As a result of combustion, high pressure is developed. Due to the expansion of gases the piston is pushed outwards. The momentum gained by the piston maintains the three strokes. Spent gases are thrown out of the cylinder during the exhaust stroke.


The working cycle of a typical diesel engine consists of four strokes: Intake stroke, Compression stroke, Expansion stroke or power stroke and Exhaust stroke. The changes that take place in the engine during each of the strokes are described below:

(a) Intake stroke: The piston moves slightly away from the head of the engine causing a low pressure region inside the cylinder. This opens up the inlet valve. Filtered air enters the cylinder through the inlet valve. The outlet valve remains closed during this stroke. As the piston reaches the dead end during the intake stroke, the cylinder is filled completely with filtered air and the inlet valve gets closed.

(b) Compression stroke: Both the inlet and the outlet valves remain closed during this stroke. The piston moves towards the head of the cylinder causing the air inside the cylinder to compress. The compression of air causes enough heat to ignite the fuel. The compression stroke comes to an end with the piston reaching the dead end.

(c) Expansion stroke: Both the valves remain closed during this stroke. Just before the commencement of this stroke, a definite amount of diesel is injected into the hot air through the sprayer. The fuel immediately bursts into flame. The combustion products produced by burning of the fuel exert immense pressure on the piston. The piston gets a ‘kick’ and moves away from the head of the cylinder with great force. This stroke is also called the ‘power stroke’. This is the stroke during which mechanical work is done. The movement of the piston is transferred to the crank. The crank changes the linear motion into circular motion.

(d) Exhaust stroke: On completion of the expansion stroke, the outlet valve opens while the inlet valve continues to remain closed. The piston moves inwards towards the head of the cylinder. This pushes the exhaust gases out of the cylinder into the external environment.

The power generated during the expansion stroke sustains the motion of the piston for the next three strokes and the cycle repeats.

24. Why is a diesel engine more efficient than a petrol engine?

Diesel is a better combustible than petrol. Therefore, less diesel fuel is required to generate the same power as petrol. Secondly, petrol does not undergo combustion completely and hence there is a small wastage of fuel. This is why diesel engine is more efficient than petrol engine.

25. What is the compression ratio in a petrol engine?

The compression ratio in a petrol engine varies from 4:1 to 10:1.

26. What is the compression ratio in a diesel engine?

The compression ratio in a diesel engine varies from 4:1 to 25:1.

27. How does the fuel get ignited in a diesel engine?

Diesel engine has high compression ratio. The compression of air during the compression stroke generates high enough temperature to ignite the fuel.

28. Make a list of the uses of diesel engines.

Diesel engines are used in heavy transport vehicles. They are used in generators to produce electricity. They are used in heavy machines like concrete mixers, road construction devices where tar is mixed with crushed stones, drilling tube wells, automated sugarcane crushers etc.

29. Write a note on Emission test.

Carbon monoxide released by the automobiles as an exhaust gas, along with other gasses, is the most poisonous among them. About 70-80% of carbon monoxide entering the air is due to automobile exhaust. Even the best of the petrol or diesel engines produces carbon monoxide. Proper maintenance of an engine can reduce the production of carbon monoxide. For each type of automobiles the limit of carbon monoxide emission is prescribed by the Government through an act. This is different for different type of vehicles. For example the permitted level of emission of carbon monoxide for cars is 3%. The amount of carbon monoxide released is determined by an instrument called ‘the gas analyser’. The test conducted to determine the percentage of carbon monoxide released by an automobile is called the emission test.

30. What is spent gases?

During the power stroke, due to the enormous heat produced, the products of combustion expand suddenly pushing the piston with a great force. These gases are incapable of any further work; hence they are called spent gases.

31. Define efficiency of heat engine

The efficiency of heat engine is defined as the fraction of heat converted into useful mechanical work. It is usually expressed as a percentage.


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  1. sir can u put the notes and question banks soon coz tmrw we hav science exm and der are 12 lessons stil 1 chapter is pending.but its really helpful for us

  2. thank helped me a lot.if you can please put the additional fill in the blanks also.