krit.club logo

Heat - Methods of Heat Transfer (Conduction, Convection, Radiation)

Grade 7ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

Heat is a form of energy that flows from a body at a higher temperature to a body at a lower temperature until thermal equilibrium is reached.

•

Conduction is the process of heat transfer in solids where heat energy is passed from one particle to another through collisions without the actual movement of the particles from their positions.

•

Good conductors (like CuCu and AlAl) allow heat to pass easily, while insulators (like wood, plastic, and glass) do not.

•

Convection is the mode of heat transfer in fluids (liquids and gases) where heat is carried by the actual movement of the heated particles of the medium, forming convection currents.

•

Radiation is the transfer of heat that does not require any material medium; it travels through vacuum in the form of infra-red electromagnetic waves at the speed of light (3×108 m/s3 \times 10^8 \text{ m/s}).

•

A black or dull surface is a better absorber and a better radiator of heat compared to a white or shiny surface.

•

Sea Breeze: During the day, land heats up faster than the sea. Warm air above land rises, and cool air from the sea blows towards the land.

•

Land Breeze: At night, land cools down faster than the sea. Warm air above the sea rises, and cool air from the land blows towards the sea.

📐Formulae

C5=F−329\frac{C}{5} = \frac{F - 32}{9}

K=C+273.15K = C + 273.15

Q=m⋅c⋅ΔTQ = m \cdot c \cdot \Delta T

ΔT=Tfinal−Tinitial\Delta T = T_{final} - T_{initial}

💡Examples

Problem 1:

Convert a body temperature of 37∘C37^\circ C into Fahrenheit (∘F^\circ F).

Solution:

F=(95×37)+32=66.6+32=98.6∘FF = \left( \frac{9}{5} \times 37 \right) + 32 = 66.6 + 32 = 98.6^\circ F

Explanation:

Using the temperature conversion formula, we substitute C=37C = 37 to find the equivalent temperature on the Fahrenheit scale.

Problem 2:

Why are the handles of cooking utensils often made of plastic or wood?

Solution:

To prevent heat from reaching the hand via conduction.

Explanation:

Plastic and wood are insulators (poor conductors of heat). They do not allow the heat energy from the metal pot to transfer to the user's hand, ensuring safety.

Problem 3:

Calculate the amount of heat energy required to raise the temperature of 2 kg2 \text{ kg} of water by 10∘C10^\circ C. (Specific heat capacity of water c=4200 J/kg∘Cc = 4200 \text{ J/kg}^\circ C)

Solution:

Q=2 kg×4200 J/kg∘C×10∘C=84,000 JQ = 2 \text{ kg} \times 4200 \text{ J/kg}^\circ C \times 10^\circ C = 84,000 \text{ J}

Explanation:

Using the formula Q=m⋅c⋅ΔTQ = m \cdot c \cdot \Delta T, where m=2m = 2, c=4200c = 4200, and ΔT=10\Delta T = 10.