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AFCAT Heat & Temperature

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This page covers AFCAT Heat & Temperature with complete concept notes, 3 graded practice MCQs, key points and exam-specific tips. Free to study.

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Concept Notes

Heat & Temperature— Rules & Concept

1.Core Concept

Read this first — the foundation of the topic

HEAT & TEMPERATURE — CORE CONCEPT Heat and Temperature are two different things. Students often confuse them. Let us understand both clearly.

Heat is a form of energy. It flows from a hotter object to a cooler object. Heat is measured in Joules (J) or Calories (cal). 1 calorie = 4.2 Joules. Temperature is the measure of how hot or cold an object is. It tells us the degree of hotness. Temperature is measured in Celsius (°C), Fahrenheit (°F), or Kelvin (K).

2.Key Rules

Core rules you must know cold
Example

A large bucket of water at 30°C has more heat energy than a small cup of water at 80°C. 4. Specific Heat Capacity (s) — This is the amount of heat needed to raise the temperature of 1 kg of a substance by 1°C. Water has the highest specific heat = 4200 J/kg°C. This is why water is used as a coolant. 5

Heat always flows by three methods

Conduction (solids), Convection (liquids and gases), Radiation (no medium needed — like sunlight).

3.Formula Block

Memorise — at least one formula appears in every paper
Heat Formula: Q = m × s × ΔT
Q = Heat energy (in Joules)
m = Mass of substance (in kg)
s = Specific heat capacity (in J/kg°C)
ΔT = Change in temperature (Final Temp − Initial Temp)
°C to °F → F = (9/5 × C) + 32
°F to °C → C = 5/9 × (F − 32)
°C to K → K = C + 273
K to °C → C = K − 273
Note: 0°C = 273 K = 32°F. Absolute Zero = 0 K = −273°C.

Where:

Temperature Conversion Formulas:

4.Exam Patterns

What examiners ask — read before attempting PYQs

RRB Group D commonly asks: - Direct conversion between Celsius, Fahrenheit, and Kelvin -

5.When to Use

Quickly decide which method to apply in the exam

of heat transfer applies to a situation (sun heating earth = Radiation) - Specific heat of water based problems - Finding Q using the formula Q = msΔT - Comparing heat content vs temperature SHORTCUT / TRICK Trick 1 — Temperature Conversion

6.Memory Hook

Remember this — never confuse the two again

To convert Celsius to Fahrenheit, remember: Double it, subtract 10%, add 32. Example: 100°C → Double = 200, subtract 10% = 180, add 32 = 212°F. ✓ Fast and accurate! Trick 2 — Kelvin is always POSITIVE. If any option shows a negative Kelvin value, reject it immediately. Minimum Kelvin = 0 K (Absolute Zero).

7.Worked Example

Solve this step-by-step before moving on
1
Step 1

Write the formula → Q = m × s × ΔT

2
Step 2

Find ΔT = 70 − 20 = 50°C

3
Step 3

Put values → Q = 2 × 4200 × 50

4
Step 4

Calculate → Q = 420,000 J = 4.2 × 10⁵ J Answer: 4,20,000 Joules or 420 kJ

8.Exam Traps

Common mistakes students make — avoid these

Students mix up Heat and Temperature. Remember: A large cold object can have MORE heat energy than a small hot object. Heat depends on mass AND specific heat AND temperature.

Temperature alone does not decide heat content. Also, never forget to add 273 when converting °C to Kelvin — losing that step costs marks.

Key Points to Remember

  • Heat is energy measured in Joules; Temperature is degree of hotness measured in °C, °F, or Kelvin.
  • Heat always flows from higher temperature to lower temperature — never the other way.
  • Formula: Q = m × s × ΔT, where Q = heat, m = mass, s = specific heat, ΔT = temperature change.
  • Specific heat of water = 4200 J/kg°C — highest among common substances, making it ideal as a coolant.
  • Temperature conversion: °C to K = add 273; °C to °F = multiply by 9/5 then add 32.
  • Absolute Zero = 0 Kelvin = −273°C — the lowest possible temperature; no negative Kelvin exists.
  • Three modes of heat transfer: Conduction (solids), Convection (liquids/gases), Radiation (no medium needed).
  • Thermal Equilibrium occurs when two bodies reach the same temperature and heat exchange stops.

Exam-Specific Tips

  • Specific heat capacity of water = 4200 J/kg°C (or 1 cal/g°C) — highest among common substances.
  • 1 Calorie = 4.2 Joules (this conversion is directly asked in MCQs).
  • Absolute Zero = 0 Kelvin = −273°C — below this temperature, nothing can exist.
  • 0°C = 273 K = 32°F — this three-way equivalence is a favourite exam fact.
  • 100°C = 373 K = 212°F — the boiling point of water in all three scales.
  • Radiation is the only mode of heat transfer that does not need any medium — this is how the Sun heats the Earth.
  • Normal human body temperature = 37°C = 98.6°F = 310 K.
  • Mercury thermometers measure temperature because mercury expands uniformly with heat and has a wide liquid range (−39°C to 357°C).
Practice MCQs

Heat & Temperature — Practice Questions

3graded MCQs · easy to hard · full solution & trap analysis

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Practice 1easy

A thermometer shows a reading of 30°C. What is this temperature in Kelvin (K)?

Practice 2medium

A metal rod of length 1 m at 0°C expands to 1.002 m when heated to 100°C. What is the coefficient of linear expansion of the metal?

Practice 3hard

A metal rod of length 1.0 m at 20°C expands to 1.002 m when heated to 70°C. What is the linear expansion coefficient (α) of the metal? (Use the formula: ΔL = α × L₀ × ΔT)

60-Second Revision — Heat & Temperature

  • Formula: Q = m × s × ΔT — memorise the order: mass × specific heat × temperature change.
  • Remember: °C to K → add 273; K to °C → subtract 273. Never skip this step.
  • Trick: To convert °C to °F quickly → double the °C, subtract 10%, then add 32.
  • Trap: High temperature does NOT mean more heat — heat also depends on mass and specific heat capacity.
  • Remember: Water has specific heat 4200 J/kg°C — highest of common substances, used as coolant in engines.
  • Three heat transfer modes — Conduction (solid), Convection (liquid/gas), Radiation (no medium) — Sun uses Radiation.
  • Absolute Zero = 0 K = −273°C. Any MCQ option showing negative Kelvin is always WRONG — eliminate immediately.
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