10th Science - Book Back Answers - Physics Unit 3 - English Medium Guides

 

SSLC / 10th - Science - Book Back Answers - Physics Unit 3 - English Medium

Tamil Nadu Board 10th Standard  Science - Physics Unit 3: Book Back Answers and Solutions

    This post covers the book back answers and solutions for Unit 3 – Physics from the Tamil Nadu State Board 10th Standard  Science textbook. These detailed answers have been carefully prepared by our expert teachers at KalviTips.com.

    We have explained each answer in a simple, easy-to-understand format, highlighting important points step by step under the relevant subtopics. Students are advised to read and memorize these subtopics thoroughly. Once you understand the main concepts, you’ll be able to connect other related points with real-life examples and confidently present them in your tests and exams.

    By going through this material, you’ll gain a strong understanding of Physics Unit 3 along with the corresponding book back questions and answers (PDF format).

Question Types Covered:

• 1 Mark Questions: Choose the correct answer, Fill in the blanks, Identify the correct statement, Match the following 
• 2 Mark Questions: Answer briefly 
• 3, 4, and 5 Mark Questions: Answer in detail

All answers are presented in a clear and student-friendly manner, focusing on key points to help you score full marks.

All the best, Class 10 students! Prepare well and aim for top scores. Thank you!

Topic: Thermal Physics

I. Choose the correct Answer

1. The value of universal  $\frac{V}{T}$ gas constant:

(a) 3.81 mol-1 K^-1
(b) 8.03 mol-1 K^-1
(c) 1.38 mol-1 K^-1
(d) 8.31 mol-1 K^-1
Answer Key:
(d) 8.31 mol-1 K^-1

 

2. If a substance is heated or cooled, the change in mass of that substance is:
(a) positive
(b) negative
(c) zero
(d) none of the above
Answer Key:
(b) negative

3. If a substance is heated or cooled, the linear expansion occurs along the axis of ______.
(a) X or -X
(b) Y or -Y
(c) both (a) and (b)
(d) either (a) or (b).
Answer Key:
(c) both (a) and (b)

4. Temperature is the average of the molecules of a substance.
(a) difference in K.E and P.E
(b) sum of P.E and K.E
(c) difference in T.E and P.E
(d) difference in K.E and T.E
Answer Key:
(b) sum of P.E and K.E

5. In the Given diagram, the possible direction of heat energy transformation is:

(a) A ← B, A ← C, B ← C
(b) A → B, A → C, B → C
(c) A → B, A ← C, B → C
(d) A ← B, A → C, B ← C
Answer Key:
(a) A ← B, A ← C, B ← C

 

II. Fill in the blanks

1. The value of Avogadro number ………..

2. The temperature and heat are ……….. quantities.

3. One calorie is the amount of heat energy required to raise the temperature of ……….. of water through

4. According to Boyle’s law, the shape of the graph between pressure and reciprocal of volume is …………

Answer Key:

1. 6.023 × 10²³

2. Inter convertible

3. 1 gram, 1°C

4. A straight line.

III. State whether the following statements are true or false.  if  false explain why?

1. For a given heat in liquid, the apparent expansion is more than that of real expansion.
2. Thermal energy always flows from a system at higher temperature to a system at lower temperature.
3. According to Charles’s law, at constant pressure, the temperature is inversely proportional to volume.
Answer key:
1. True
2. True
3. False – According to Charles law, at constant pressure, the volume is directly proportional to temperature.

IV.  Match the following  

Column I	Column II
1. Linear expansion	a. change in volume
2. Superficial expansion	b. hot body to cold body
3. Cubical expansion	c. 1.381 X 10-23 JK-1
4. Heat transformation	d. change in length
5. Boltzmann constant	e. change in area

Answer Key:

Column I	Column II
1. Linear expansion	a. change in length
2. Superficial expansion	b. change in area
3. Cubical expansion	c. change in volume
4. Heat transformation	d. hot body to cold body
5. Boltzmann constant	e. 1.381 X 10-23 JK-1

V.  Assertion & Reasoning

(a) Both the assertion and the reason are true and the reason is the correct explanation of the assertion.
(b) Both the assertion and the reason are true but the reason is not the correct explanation of the assertion.
(c) The assertion is true but the reason is false.
(d) The assertion is false but the reason is true.
1. Assertion: There is no effects on other end when one end of the rod is only heated.
Reason: Heat always flows from a region of lower temperature to higher temperature of the rod.
2. Assertion: Gas is highly compressible than solid and liquid
Reason: Interatomic or intermolecular distance in the gas is comparably high.
Answer Key:
1. (b)
2. (a)

 

VI. Answer  briefly

Question 1.

Define one calorie.

Answer Key:

One calorie is defined as the amount of heat energy required to rise the temperature of 1 gram of water through 1°C.

 

Question 2.
Distinguish between linear and superficial areal expansion.
Answer Key:

Linear Expansion	Areal and Superficial Expansion
In this expansion, length of a body increases	In this expansion, area of a body increases
Coefficient of linear expansion is different for different materials.	Coefficient of Areal expansion is different for different materials.
$\frac{△L}{L_{\circ }}={\alpha }_L△T$	$\frac{△A}{A_{\circ }}={\alpha }_A△T$

 

Question 3.
What is the coefficient of cubical expansion?
Answer Key:
The ratio of increase in the volume of the body per degree rise in temperature to its unit volume is called a coefficient of cubical expansion.

Question 4.

State Boyle’s law

Answer Key:

When the temperature of a gas is kept constant, the volume of a fixed mass of gas is inversely proportional to its pressure.
P ∝ 1 / V

 

Question 5.

State-the law of volume.

Answer Key:

When the pressure of a gas is kept constant, the volume of a gas is directly proportional to the temperature of the gas.
i.e., V ∝ T.
(or)
$\frac{V}{T}$= constant.

 

Question 6.
Distinguish between ideal gas and real gas.
Answer Key:

Ideal gas	Real gas
In this gas molecules or atoms of a gas interact with each other with some interatomic force.	In this gas molecules or atoms of a gas do not interact with each other.
They obey Boyle’s law, Charles law and Avogadro’s law.	They do not obey Boyle’s law, Charles law and Avogadro’s law.

Question 7.
What is co-efficient of real expansion?
Answer Key:
Coefficient of real expansion is defined as the ratio of the true rise in the volume of the liquid per degree rise in temperature to its unit volume. The SI unit of coefficient of real expansion is the K^-1.

Question 8.
What is the coefficient of apparent expansion?
Answer Key:
Coefficient of apparent expansion is defined as the ratio of the apparent rise in the volume of the liquid per degree rise in temperature to its unit volume.
The SI unit of the coefficient of apparent expansion is K^-1.

 

VII. Numerical Problems

Question 1.
Find the final temperature of a copper rod whose area of cross section changes from 10 m² to 11 m² due to heating. The copper rod is initially kept at 90 K. (Coefficient of superficial expansion is 0.0021 /K).
Answer Key:
Change in area ΔA = 11 – 10 = 1 m²
Initial temperature  T₁ = 90 K
Let Final temperature be T2K
A0 = 10 m²
Coefficient of superficial expansion is
αA = 0.0021 / k
$\frac{△A}{A_0}$ = α_AΔT
$\frac{1}{10}$= 0.0021 ΔT
∴ ΔT = 0.0021 × 10
= 0.021 

T₂ – T₁ = 0.021
T₂ – 90 = 0.021
∴ Final temperature T₂ = 90.021 K

 

Question 2.
Calculate the coefficient of cubical expansion of a zinc bar. Whose volume is increased 0.25 m³ from 0.3 m³ due to the change in its temperature of 50 K.
Answer Key:
Initial volume V0 = 0.25 m³
Final volume = 0.30 m³
Change in volume ΔV = 0.3 – 0.25 = 0.05 m³
Temperature ΔT = 50K
Coefficient of cubical expansion is 

${\alpha }_v=\frac{\Delta V}{v_0\Delta T} <br>$

$=\frac{0.05}{0.25\times 50}<br>$

$=\frac{1}{5\times 50}=\frac{1}{250}$ 

$=\frac{1000\times {10}^{-3}}{250}=4\times {10}^{-3}$ 

∴ Coefficient of Cubical expansion
αv = 0.004 /K

VIII. Answer in detail

Question 1.
Derive the ideal gas equation.
Answer Key:
The ideal gas equation is an equation, which relates all the properties of an ideal gas. An ideal gas obeys Boyle’s law and Charles’s law and Avogadro’s law.
According to Boyle’s law, PV = constant ………. (1)
According to Charles’s law,

$\frac{V}{T}$ = constant ……… (2)
According to Avogadro’s law,
$\frac{V}{T}$ = constant …….. (3)
After combining equations (1), (2) and (3), you equation. can get the following
$\frac{V}{nT}$ = constant ……. (4)
The above relation is called the combined law of gases. If you consider a gas, which contains µ moles of the gas, the number of atoms contained will be equal to µ times the Avogadro number, N0.
i.e., n = µNA
Using equation (5), in equation (4) can be written as
$\frac{PV}{\mu N_{A}T}$ = constant
The value of the constant in the above equation is taken to be KB, which is called as Boltzmann constant (1.38 × 10^-23 JK^-1). Hence, we have the following equation:
$\frac{PV}{\mu N_{A}T}$ = KB
PV = µNAKBT
µNAKB = R
which is termed as universal gas constant whose value is 8.31 J mol^-1 K^-1.

PV = RT
Ideal gas equation is also called as equation of state because it gives the relation between the state variables and it is used to describe the state of any gas.

 
Question 2.
Explain the experiment of measuring the real and apparent expansion of a liquid with a neat diagram.
Answer Key:

 

To start with, the liquid whose real and apparent expansion is to be determined is poured in a container up to a level. Mark this level as L₁. Now, heat the container and the liquid using a burner. Initially, the container receives the thermal energy and it expands. As a result, the volume of the liquid appears to have reduced. Mark this reduced level of liquid as L₂. On further heating, the thermal energy supplied to the liquid through the container results in the expansion of the liquid. Hence, the level of liquid rises to L₃. Now, the difference between the levels L₁ and L₃ is called as apparent expansion, and the difference between the levels L2 and L3 is called real expansion. The real expansion is always more than that of apparent expansion.
Real expansion =L₃ – L₂

Apparent expansion = L₃ – L₁

 

IX.  Hot questions

Question 1.
If you keep ice at 0°C and water at 0°C in either of your hands, in which hand you will feel more chillness? Why?
Answer Key:
The hand consisting of ice at 0°C would feel more chillness because, ice undergoes melting. More amount of energy (chillness) is transferred to hand. In addition ice has latent heat of fusion.