# Heat - Grade 10 (SEE) Physics
## Complete Chapter Notes with All Exercises - NEB Curriculum 2080

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## 🎯 Chapter Overview
Step into the intriguing realm of **Heat Class 10 Science** as we explore the fascinating world of thermal energy! This comprehensive chapter provides deep insights into the nature of heat and its applications in our everyday lives. From understanding temperature to exploring heat transfer mechanisms, this chapter delves into the fundamental principles of heat in a clear and engaging manner.

**Weightage:** 12-15 marks in SEE examination
**Time Required:** 25-30 periods

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## 📚 Learning Objectives
After studying this chapter, students will be able to:
- Understand the concept of heat as a form of energy
- Distinguish between heat and temperature clearly
- Apply the heat equation to solve numerical problems
- Explain different modes of heat transfer
- Understand calorimetry principles
- Analyze anomalous expansion of water

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## 🔥 1. INTRODUCTION TO HEAT

### 1.1 Definition of Heat
Heat is a form of energy that gives us the sensation of warmth. Heat is the **sum total of kinetic energy** contained by the molecules in a body.

**Modern Definition:** Heat is the energy transferred due to temperature difference between two systems.

### 1.2 Heat as Energy
Heat energy is produced when molecules in a body start vibrating or moving around. The faster the molecules move, the more heat is produced in that body.

**Key Points:**
- Heat always flows from hotter body to colder body
- Heat is a cause, temperature is an effect
- Amount of heat depends on mass and average kinetic energy of molecules

### 1.3 Units of Heat
**SI Unit:** Joule (J)
**CGS Unit:** Calorie (cal)

**Relationship:** 
```
4.2 J = 1 cal
1 cal = 4.2 J
```

**Definition of Calorie:** The amount of heat required to raise the temperature of 1 gram of pure water by 1°C at standard atmospheric pressure.

### 1.4 Device to Measure Heat
**Calorimeter** is used to measure heat energy of a body.

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## 🌡️ 2. TEMPERATURE

### 2.1 Definition
Temperature is the measure of how hot or cold a body is. It is the **average kinetic energy** of molecules present in a body.

### 2.2 Difference Between Heat and Temperature

| Heat | Temperature |
|------|-------------|
| Sum of kinetic energy of molecules | Average kinetic energy of molecules |
| SI unit: Joule (J) | SI unit: Kelvin (K) |
| Measured by calorimeter | Measured by thermometer |
| It is a cause | It is an effect |
| It flows from one body to another | It doesn't flow |
| Depends on mass of body | Independent of mass |
| Energy form | Degree of hotness/coldness |

### 2.3 Temperature Scales
**Three temperature scales:**
1. **Celsius Scale (°C):** Lower fixed point = 0°C, Upper fixed point = 100°C
2. **Fahrenheit Scale (°F):** Lower fixed point = 32°F, Upper fixed point = 212°F
3. **Kelvin Scale (K):** Lower fixed point = 273K, Upper fixed point = 373K

### 2.4 Temperature Conversion Formula
```
(C - 0)/100 = (F - 32)/180 = (K - 273)/100
```

**Simplified Relations:**
- C = (F - 32) × 5/9
- F = (C × 9/5) + 32
- K = C + 273

### 2.5 Thermometer
**Device:** Thermometer is used to measure temperature
**Principle:** "Substances expand on heating and contract on cooling"
**Normal human body temperature:** 37°C or 98.6°F

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## ⚖️ 3. HEAT EQUATION

### 3.1 Derivation of Heat Equation
Let a body of mass 'm' have initial temperature 't₁' and final temperature 't₂' when heat 'Q' is supplied.

**Heat gained/lost (Q) ∝ mass of body (m)**  ... (i)
**Heat gained/lost (Q) ∝ change in temperature (Δt)** ... (ii)

Combining (i) and (ii):
**Q ∝ m × Δt**

Therefore: **Q = ms Δt**

Where 's' is the specific heat capacity of the substance.

### 3.2 Heat Equation Formula
```
Q = ms Δt

Where:
Q = Amount of heat (J)
m = Mass of body (kg)
s = Specific heat capacity (J/kg°C)
Δt = Change in temperature (°C)
```

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## 🔬 4. SPECIFIC HEAT CAPACITY

### 4.1 Definition
Specific heat capacity is the amount of heat gained or lost by a substance of mass 1 kg to change its temperature by 1°C or 1K.

**Formula:**
```
s = Q/(m × Δt)

SI Unit: J/kg°C
```

### 4.2 Physical Meaning
**When we say specific heat capacity of water is 4200 J/kg°C:**
This means 4200 J of energy is needed to raise the temperature of 1 kg of water by 1°C.

### 4.3 Properties
- Different substances have different specific heat capacities
- Substances with higher specific heat capacity heat up and cool down slowly
- Substances with lower specific heat capacity heat up and cool down quickly
- Water has the highest specific heat capacity (4200 J/kg°C)

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## 🔄 5. PRINCIPLE OF CALORIMETRY

### 5.1 Statement
**"The amount of heat lost by a hotter body is equal to the amount of heat gained by a colder body when they are kept in thermal contact."**

**Mathematical Expression:**
```
Heat lost = Heat gained
m₁s₁Δt₁ = m₂s₂Δt₂
```

### 5.2 Applications
- Used in calorimeter to measure heat
- Mixing of hot and cold liquids
- Heat transfer calculations
- Finding specific heat capacity of substances

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## 🌊 6. ANOMALOUS EXPANSION OF WATER

### 6.1 Definition
The unusual behavior of water between 0°C to 4°C is called anomalous expansion of water.

### 6.2 Behavior
**Normal Expansion:** Substances expand on heating and contract on cooling
**Anomalous Expansion:** Water contracts when heated from 0°C to 4°C and expands when cooled from 4°C to 0°C

### 6.3 Key Points
- Water has **maximum density** at 4°C
- Water has **minimum volume** at 4°C
- Below 4°C, water expands instead of contracting
- Above 4°C, water shows normal expansion

### 6.4 Significance
**Preservation of Aquatic Life:**
- In winter, water at 4°C (densest) stays at the bottom
- Ice forms on the surface first
- Ice acts as insulator, protecting aquatic life below
- This prevents complete freezing of water bodies

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## 🔥 7. HEAT TRANSFER

### 7.1 Modes of Heat Transfer
Heat can be transferred by three methods:
1. **Conduction**
2. **Convection** 
3. **Radiation**

### 7.2 Conduction
**Definition:** Transfer of heat through a material without movement of the material itself.

**Process:** Heat transfers through molecular vibrations and collisions
**Medium:** Mainly occurs in solids
**Example:** Heat transfer through metal rod

**Characteristics:**
- Requires direct contact
- No movement of particles
- Efficient in metals (good conductors)
- Poor in non-metals (insulators)

### 7.3 Convection
**Definition:** Transfer of heat through movement of fluids (liquids and gases).

**Process:** Hot fluid becomes less dense, rises up; cold fluid becomes denser, sinks down
**Medium:** Occurs in liquids and gases
**Example:** Heating water in a pot, air circulation

**Characteristics:**
- Requires movement of fluid particles
- Creates convection currents
- Cannot occur in solids
- Natural and forced convection possible

### 7.4 Radiation
**Definition:** Transfer of heat through electromagnetic waves without requiring any medium.

**Process:** Heat transfers through electromagnetic radiation
**Medium:** Can occur in vacuum (no medium required)
**Example:** Heat from sun, heat from fire

**Characteristics:**
- Fastest mode of heat transfer
- Can travel through vacuum
- All objects emit and absorb radiation
- Follows laws of reflection and refraction

### 7.5 Comparison of Heat Transfer Methods

| Conduction | Convection | Radiation |
|------------|------------|-----------|
| Through direct contact | Through fluid movement | Through electromagnetic waves |
| Mainly in solids | In liquids and gases | In all media including vacuum |
| Particles don't move | Particles move | No particles required |
| Slowest | Moderate speed | Fastest |
| Does not follow reflection laws | Does not follow reflection laws | Follows reflection laws |

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## 📋 8. COMPLETE EXERCISE SOLUTIONS

### **1. Choose the correct options:**

**a. Which statement defines heat?**
(i) total kinetic energy of molecules ✓
(ii) average kinetic energy of molecules
(iii) sum of kinetic energy and potential energy
(iv) energy transmitted due to difference in temperature

**Answer:** (i) total kinetic energy of molecules

**b. The SI unit of heat is:**
(i) calorie (ii) joule ✓ (iii) watt (iv) pascal

**Answer:** (ii) joule

**c. Specific heat capacity depends on:**
(i) mass (ii) volume (iii) temperature (iv) nature of substance ✓

**Answer:** (iv) nature of substance

**d. Water has maximum density at:**
(i) 0°C (ii) 4°C ✓ (iii) 100°C (iv) 37°C

**Answer:** (ii) 4°C

### **2. Answer the following questions:**

**a. Define heat. Write its SI unit.**

**Answer:** Heat is a form of energy that gives sensation of warmth OR the sum of kinetic energy of molecules present in a body.
**SI Unit:** Joule (J)

**b. What is temperature? How is it measured?**

**Answer:** Temperature is the measure of hotness or coldness of a body OR average kinetic energy of molecules in a body.
**Measurement:** Temperature is measured using thermometer.

**c. Write the relationship between joule and calorie.**

**Answer:** 4.2 J = 1 cal or 1 cal = 4.2 J

**d. State the principle of calorimetry.**

**Answer:** The principle of calorimetry states that "The amount of heat lost by hotter body equals the amount of heat gained by colder body when they are in thermal contact."

**e. Define specific heat capacity. Write its SI unit.**

**Answer:** Specific heat capacity is the amount of heat required to raise the temperature of 1 kg of substance by 1°C or 1K.
**SI Unit:** J/kg°C

**f. What is anomalous expansion of water?**

**Answer:** The unusual behavior of water between 0°C to 4°C where it contracts on heating and expands on cooling is called anomalous expansion of water.

**g. Name the three modes of heat transfer.**

**Answer:** 
1. Conduction
2. Convection
3. Radiation

**h. Convert 25°C into Fahrenheit scale.**

**Solution:**
Given: C = 25°C, F = ?

Using: (C - 0)/100 = (F - 32)/180
(25 - 0)/100 = (F - 32)/180
25/100 = (F - 32)/180
F - 32 = (25 × 180)/100 = 45
F = 45 + 32 = 77°F

**Answer:** 25°C = 77°F

### **3. Distinguish between:**

**a. Heat and Temperature**

| Heat | Temperature |
|------|-------------|
| Sum of kinetic energy | Average kinetic energy |
| SI unit: Joule | SI unit: Kelvin |
| Measured by calorimeter | Measured by thermometer |
| Cause | Effect |
| Flows from one body to another | Doesn't flow |

**b. Conduction and Convection**

| Conduction | Convection |
|------------|------------|
| Heat transfer through direct contact | Heat transfer through fluid movement |
| Occurs mainly in solids | Occurs in liquids and gases |
| No movement of particles | Movement of particles occurs |
| Slower process | Faster than conduction |

**c. Good conductors and Bad conductors**

| Good Conductors | Bad Conductors (Insulators) |
|-----------------|---------------------------|
| Allow heat to pass easily | Do not allow heat to pass easily |
| Examples: Metals (copper, iron) | Examples: Wood, plastic, air |
| Have free electrons | No free electrons |
| Used in cooking utensils | Used for insulation |

### **4. Give reasons:**

**a. Metals are good conductors of heat.**

**Answer:** Metals have free electrons that can move easily and transfer kinetic energy from one atom to another, making them good conductors of heat.

**b. Water is used in car radiators.**

**Answer:** Water has high specific heat capacity (4200 J/kg°C), so it can absorb large amount of heat with small temperature rise, making it effective coolant.

**c. We feel cool under a tree.**

**Answer:** Trees provide shade, blocking direct sun's radiation. Also, transpiration from leaves cools the surrounding air through evaporation.

**d. Ice floats on water.**

**Answer:** Due to anomalous expansion, ice has lower density than water at 0°C, so it floats on water surface.

**e. Aquatic animals can survive in frozen lakes.**

**Answer:** Due to anomalous expansion of water, ice forms only on the surface while water remains liquid below, allowing aquatic life to survive.

**f. We can see the heat waves above a hot road.**

**Answer:** Hot air above the road has different density than cooler air, causing light to bend and creating visible heat waves through refraction.

**g. Woolen clothes keep us warm in winter.**

**Answer:** Wool traps air between its fibers. Air is a poor conductor of heat, so it acts as insulation, preventing body heat from escaping.

### **5. Numerical Problems:**

#### **Problem Type 1: Heat Equation**

**Q1:** Calculate the amount of heat required to change temperature of 3 kg iron from 30°C to 200°C. (Specific heat capacity of iron = 460 J/kg°C)

**Given:**
- m = 3 kg
- Initial temperature (t₁) = 30°C
- Final temperature (t₂) = 200°C
- s = 460 J/kg°C

**Solution:**
Δt = t₂ - t₁ = 200 - 30 = 170°C
Q = msΔt = 3 × 460 × 170 = 234,600 J

**Answer:** Heat required = 234,600 J or 234.6 kJ

**Q2:** 2400 J heat is given to 2 kg iron at 20°C. Find final temperature. (s = 460 J/kg°C)

**Given:**
- Q = 2400 J
- m = 2 kg
- t₁ = 20°C
- s = 460 J/kg°C

**Solution:**
Q = msΔt
2400 = 2 × 460 × (t₂ - 20)
2400 = 920 × (t₂ - 20)
t₂ - 20 = 2400/920 = 2.61
t₂ = 20 + 2.61 = 22.61°C

**Answer:** Final temperature = 22.61°C

#### **Problem Type 2: Calorimetry**

**Q3:** Hot water at 100°C is mixed with 300g of water at 0°C until final temperature becomes 40°C. Find mass of hot water added.

**Given:**
- Hot water temperature = 100°C
- Cold water mass = 300g = 0.3 kg
- Cold water temperature = 0°C
- Final temperature = 40°C

**Solution:**
Let mass of hot water = m₁

Using principle of calorimetry:
Heat lost by hot water = Heat gained by cold water
m₁ × s × (100 - 40) = 0.3 × s × (40 - 0)
m₁ × 60 = 0.3 × 40
m₁ = (0.3 × 40)/60 = 0.2 kg

**Answer:** Mass of hot water = 0.2 kg or 200g

**Q4:** Find specific heat capacity of water if 2.1 × 10⁵ J heat raises temperature of 2 kg water from 40°C to 65°C.

**Given:**
- Q = 2.1 × 10⁵ J
- m = 2 kg
- t₁ = 40°C, t₂ = 65°C

**Solution:**
Δt = 65 - 40 = 25°C
s = Q/(m × Δt) = (2.1 × 10⁵)/(2 × 25) = 210,000/50 = 4200 J/kg°C

**Answer:** Specific heat capacity = 4200 J/kg°C

#### **Problem Type 3: Temperature Conversion**

**Q5:** Convert 37°C to Fahrenheit scale.

**Solution:**
F = (C × 9/5) + 32 = (37 × 9/5) + 32 = 66.6 + 32 = 98.6°F

**Answer:** 37°C = 98.6°F

**Q6:** Convert 273K to Celsius scale.

**Solution:**
C = K - 273 = 273 - 273 = 0°C

**Answer:** 273K = 0°C

#### **Problem Type 4: Mixed Problems**

**Q7:** How much heat is needed to raise temperature of 5 kg water from 20°C to 100°C?

**Given:**
- m = 5 kg
- t₁ = 20°C, t₂ = 100°C
- s = 4200 J/kg°C

**Solution:**
Q = msΔt = 5 × 4200 × (100 - 20) = 5 × 4200 × 80 = 1,680,000 J = 1680 kJ

**Answer:** Heat required = 1680 kJ

**Q8:** If 50,000 J heat is supplied to 10 kg water, what is the rise in temperature?

**Given:**
- Q = 50,000 J
- m = 10 kg
- s = 4200 J/kg°C

**Solution:**
Δt = Q/(ms) = 50,000/(10 × 4200) = 50,000/42,000 = 1.19°C

**Answer:** Temperature rise = 1.19°C

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## 📈 9. IMPORTANT FORMULAS SUMMARY

### **Heat and Temperature**
- Q = msΔt (Heat equation)
- s = Q/(mΔt) (Specific heat capacity)
- (C-0)/100 = (F-32)/180 = (K-273)/100 (Temperature conversion)

### **Temperature Conversions**
- F = (C × 9/5) + 32
- C = (F - 32) × 5/9
- K = C + 273

### **Calorimetry**
- Heat lost = Heat gained
- m₁s₁Δt₁ = m₂s₂Δt₂

### **Constants**
- 1 cal = 4.2 J
- Specific heat of water = 4200 J/kg°C
- Water density maximum at 4°C

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## 🎯 10. EXAM PREPARATION TIPS

### **Theory Questions (2-3 marks)**
- Learn exact definitions with SI units
- Understand anomalous expansion clearly
- Practice temperature conversion formulas
- Remember all three modes of heat transfer

### **Numerical Problems (3-4 marks)**
- Master the heat equation Q = msΔt
- Practice calorimetry problems extensively
- Temperature conversion problems are common
- Show all calculation steps clearly

### **Give Reason Questions (2-3 marks)**
- Connect to daily life examples
- Use scientific principles to explain
- Focus on anomalous expansion applications
- Explain heat transfer in real situations

### **Long Questions (5-6 marks)**
- Complete derivation of heat equation
- Detailed explanation of calorimetry principle
- Modes of heat transfer with examples
- Anomalous expansion and its significance

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## 🏆 11. PREVIOUS YEAR SEE QUESTIONS PATTERN

### **Theory Questions**
- Definition of heat and temperature
- Principle of calorimetry
- Anomalous expansion of water
- Modes of heat transfer
- Specific heat capacity concept

### **Numerical Questions**
- Heat equation problems
- Temperature conversion
- Calorimetry calculations
- Specific heat capacity finding
- Mixed hot and cold water problems

### **Common Diagrams**
- Temperature vs time graph for water
- Heat transfer modes illustration
- Calorimeter diagram
- Anomalous expansion graph

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## ✅ 12. CHAPTER CHECKLIST

**Before SEE Exam, ensure you can:**
- [ ] Define heat and temperature clearly
- [ ] Apply heat equation Q = msΔt correctly
- [ ] Solve calorimetry problems step by step
- [ ] Convert between temperature scales
- [ ] Explain anomalous expansion of water
- [ ] Describe all three heat transfer modes
- [ ] Give scientific reasons for daily phenomena
- [ ] Draw and interpret temperature graphs

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## 🎊 CONCLUSION

Heat is a fundamental chapter that connects thermal energy concepts with daily life applications. The chapter builds strong foundation for understanding energy transfer, temperature effects, and thermal properties of matter. Master the heat equation, practice numerical problems regularly, and understand the scientific explanations behind everyday thermal phenomena.

**Success Formula:** 
Clear Concepts + Formula Practice + Daily Life Connections = Perfect Heat Mastery!

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*This comprehensive note covers the complete Heat chapter as per NEB curriculum 2080, designed to enhance your scientific knowledge and help you grasp the significance of heat in our everyday lives. Through detailed explanations and practical examples, unlock the secrets of thermal energy in an informative and enjoyable way!*

**📞 Need Help?** Practice more numerical problems and focus on understanding the principle of calorimetry for complete chapter mastery.

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