Physics 6 Lesson 20: Thermal expansion of gases prepared by Le Hong Phong High School hopes to provide useful materials to help students master the lesson knowledge and achieve good results in exams and tests. on class.
Summary of Physics 6 Lesson 20
Thermal expansion of a gas
– Gases both expand when heated and contract when cooled.
For example:
Insert a small glass tube through the stopper of the flask.
Place a drop of colored water in a glass tube.
Tighten the rubber stopper with the glass tube containing colored water into the flask.
Rub your palms together to warm up, then press firmly against the flask.
Phenomenon: The drop of colored water goes up, indicating that the volume of the gas increases, the gas in the bottle expands. Stop putting your hand on the flask, the drop of colored water goes down, indicating that the volume of the gas decreases, the gas in the bottle shrinks.
Example: Hot air balloons use hot air and carry people up high. Balloons are used in science to understand the atmosphere, observe astronomical … Or sky lanterns are released on the night of the festival.
– different gases have the same thermal expansion.
Table 1. The volume increase of 1000 cm3 of some substances when the temperature is increased by 500C.
Note
Unlike solids and liquids, all gases have the same thermal expansion.
For gases, thermal expansion is also mass expansion.
Compare the thermal expansion of substances
From Table 1 we see:
Gases expand more with heat than liquids, liquids expand with heat more than solids
Solution method
explain phenomena in life
To explain the phenomena in life, we rely on the thermal expansion properties of the following gases:
– Gases both expand when heated and contract when cooled.
– gases that are different but thermally expand are the same.
– Gases expand more with heat than liquids, liquids expand with heat more than solids.
The gas is compressible and takes up the entire volume of the container.
Solve exercises in Physics textbook 6 Lesson 20
Lesson C1 (page 62 Physics Textbook 6)
What happens to the colored water droplet in the glass tube when the hand is pressed against the flask? This phenomenon shows how the volume of air in the tank changes?
The answer:
When the hand is pressed against the flask, there is a phenomenon: the drop of water is transported to the top. This phenomenon shows that the volume of air has increased as it heats up.
Lesson C2 (page 62 of Physics Textbook 6)
When we stop putting our hands on the flask, what happens to the colored water drop in the glass tube? What does this phenomenon prove?
The answer:
When we stop putting our hands on the flask, there is a phenomenon of water drops moving down the glass tube. This phenomenon shows that the volume of air in the tank decreases as it cools.
Lesson C3 (page 63 Physics Textbook 6)
Why does the volume of air in the flask increase when two hot hands are placed on the flask?
The answer:
The volume of air in the flask increases again when we put a hot hand on the flask because the temperature of the hand is higher than the temperature of the flask, causing the flask to heat up and the air in the flask also heats up, so it expands.
Lesson C4 (page 63 of Physics Textbook 6)
Why does the volume of air in the flask decrease when we stop putting our hands on the flask?
The answer:
When we stop putting our hands on the flask, the temperature of the flask is higher than the temperature of the surrounding air outside, causing the temperature of the flask and the air in the flask to drop, so it shrinks.
Lesson C5 (page 63 Physics Textbook 6)
Read table 20.1 which records the volume increase of 1000 cm3 (1 liter) of some substances, when its temperature increases by 50oC and draw comments.
Table 20.1
| Gases | Liquid | Solids |
| Air: 183cm3 | Wine: 58cm3 | Aluminum: 3.45cm3 |
| quite watery: 183cm3 | Kerosene: 55cm3 | Bronze: 2.55cm3 |
| Oxygen gas: 183cm3 | Mercury: 9cm3 | Iron: 1.80cm3 |
The answer:
* Read the table by example:
The increase in volume of 1 liter of alcohol when its temperature is increased by 50oC is 58cm3.
the rest the students read the same.
* Comment:
With the same volume, when raised to the same temperature, then:
Different gases expand because of the same heat.
+ Different liquids and solids expand because of different temperatures.
Gases expand more because of heat than liquids, and liquids expand more because of heat than solids.
Lesson C6 (page 63 Physics Textbook 6)
Choose the right word to fill in the blanks of the following sentences:
a. The volume of gas in the tank (1)… when the gas is heated.
b) The volume of gas in the tank decreases when gas (2)…….
c) Solids expand due to heat (3) ……., gases expand because of heat (4) ……
Words to fill in:
– Heat up, cool down.
– Up and down.
– The most, the least.
The answer:
a. (1) increase.
b. (2) cool down.
c. (3) the least, (4) the most.
Lesson C7 (page 63 Physics Textbook 6)
What conditions must a ping-pong ball be dipped in hot water to inflate?
The answer:
When a ping-pong ball is pressed into hot water, the air in the ball is heated, expanding, causing the ball to inflate.
Therefore, the condition for the ping-pong ball to be dented and dipped in hot water to inflate is that the air inside the ball must not be lost to the outside, ie the ball is not open to air.
Lesson C8 (page 63 Physics Textbook 6)
Why is hot air lighter than cold air? (See the article on specific gravity to answer this question.)
The answer:
The specific gravity of air is determined by the formula:
Where: m is the mass of the gas, V is the volume of the gas, and d is the specific gravity.
– As the temperature increases, the mass of the gas (m) remains the same but the volume (V) increases as the gas expands, so the specific gravity (d) decreases.
⇒ So the specific gravity of hot air is less than that of cold air, i.e. hot air is lighter than cold air.
Lesson C9 (page 64 of Physics Textbook 6)
The first instrument to measure the heat and cold of mankind was invented by the Galilean anthropologist (1564 – 1642). It consists of a flask with a glass tube attached. Heat the flask and then dip the end of the glass tube into a pitcher of water. As the gas cylinder cools, water rises in the glass tube (H.20.3).
Now, based on the water level in the glass tube, one can tell whether the weather is hot or cold. Please explain why?
The answer:
– When the weather heats up, the air in the flask also heats up, expanding, pushing the water level in the glass tube down.
– When the weather cools, the air in the flask also cools, shrinking, leading to the level of water in the glass tube at that time rising.
Similarly, if a glass tube is attached to a graduated paper tape, it is possible to know when the water level drops and rises, that is, when it is hot and cold.
Physics Quiz 6 Lesson 20 (with answers)
Lesson 1: When you dip a dented ping pong ball in hot water, it will swell again. Why?
A. Because hot water causes the shell of the ball to shrink.
B. Because hot water causes the shell of the ball to expand.
C. Because hot water causes the gas in the balloon to contract.
D. Because hot water causes the gas in the balloon to expand.
The answer:
Because hot water causes the gas in the balloon to expand, ⇒ of the balloon is inflated.
ANSWER EASY
Lesson 2: When the lighter is still full of gas in the lighter, if it is exposed to the sun, it will easily explode. explain why?
A. Because when exposed to the sun, the temperature increases, the gas in liquid form will decrease in volume, causing the lighter to explode.
B. Because when exposed to the sun, the temperature increases, the gas in the gaseous form will increase in volume, causing the lighter to explode.
C. Because when exposed to the sun, the temperature increases, the gas in the gas form will decrease in volume, causing the lighter to explode.
D. Because when exposed to the sun, the temperature increases, the gas in liquid form will increase in volume, causing the lighter to explode.
The answer:
Because when exposed to the sun, the temperature increases, the gas in liquid form will increase in volume, causing the lighter to explode
Lesson 3: Which of the following is true when comparing the thermal expansion of solids, liquids, and gases?
A. Gases expand more with heat than liquids, liquids expand with heat more than solids.
B. Solids expand more heat than liquids, liquids expand more heat than gases.
C. Gases expand more with heat than solids, solids expand with heat more than liquids.
D. Liquids expand more heat than solids, solids expand more heat than gases.
The answer:
Gases expand more because of heat than liquids, liquids expand more because of heat than solids.⇒ Answer A
Exercise 4: When a gas is heated, which of the following quantities changes?
A. Both volume, density and specific gravity change.
B. Only the specific gravity changes.
C. Only the volume can change.
D. Only the density changes.
The answer:
– Mass does not depend on temperature.- Volume depends on temperature ⇒ density and specific gravity depends on temperature.
⇒Answer A
Lesson 5: When the bicycle wheel is inflated, if it is left outside in the sun, it will easily explode. explain why?
A. The increased temperature causes the wheel cover to shrink.
B. The increased temperature causes the inner wheel to expand.
C. The increased temperature causes the air in the inner wheel to contract.
D. The increased temperature causes the air in the wheel hub to expand.
The answer:
When the bicycle wheel is inflated, if it is left outside in the midday sun, the gas in the inside of the car will expand the inner wheel will easily explode⇒ Answer D
Lesson 6: Which of the following is true about the thermal expansion of air and oxygen?
A. Air expands more because of heat than oxygen.
B. Air expands because of less heat than oxygen.
C. Air and oxygen expand equally.
D. All three of the above conclusions are wrong.
The answer:
All gases expand with equal heat⇒ Answer C
Lesson 7: Choose the correct answer to fill in the blanks: the watery masses rising from the sea, rivers, and lakes are hit by sunlight, so………….., ………….., ………… and fly up to form clouds.
A. expands, heats up, lightens.
B. lighten, expand, heat up.
C. heats up, expands, lightens.
D. lighten, heat up, expand.
The answer:
Watery masses rising from the sea, rivers, and lakes are warmed by the sun’s rays, so they heat up, expand, lighten, and rise to form clouds.⇒ Answer C
Lesson 8: Which of the following statements is not true?
A. Gases expand when heated, contract when cooled.
B. different gases expand because of the same heat.
C. Gases expand more heat than liquids, liquids expand more heat than solids.
D. When a gas is heated, the volume of the gas decreases.
The answer:
When the gas is heated, the volume of the gas increases⇒ Answer D
Exercise 9: Fill in the correct word. When the temperature is decreased, the volume of…….will decrease less than the volume of…….
A. gas, liquid
B. gas, solid
C. liquid, solid
D. solid, liquid
The answer:
When the temperature is decreased, the volume of the solid will decrease less than the volume of the liquid.⇒ Answer
Lesson 10: Which of the following is true about the volume of a gas in a sealed glass vessel when heated?
A. The volume does not change because the glass jar is closed.
B. Increased volume.
C. Volume is reduced.
D. All three of the above conclusions are wrong.
The answer:
The mass of gas in a sealed glass vessel when heated, as the vessel expands, the volume of the gas in the vessel also increases.⇒ Answer B
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Physics 6 Lesson 20: Thermal expansion of gases – Solution for Physics textbook 6 Lesson 20