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The World of Metals and Non-metals - Conduction of heat

Grade 7CBSE

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

🔑Concepts

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Conduction is the process of heat transfer in solids where heat energy is passed from one particle to the next without the actual movement of the particles themselves.

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Metals are generally excellent conductors of heat because they contain free electrons that move rapidly and transfer energy. For example, Silver (AgAg) and Copper (CuCu) are among the best thermal conductors.

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Non-metals (except for graphite) are typically poor conductors of heat and are known as insulators. Examples include wood, plastic, and glass.

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The flow of heat always occurs from a region of higher temperature (ThighT_{high}) to a region of lower temperature (TlowT_{low}) until thermal equilibrium is reached.

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Practical applications: Cooking utensils are made of metals like Aluminum (AlAl) or Stainless Steel for quick heating, while their handles are made of insulators like Bakelite or wood to prevent burns.

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The rate of heat transfer is directly proportional to the temperature difference (ΔT\Delta T) between the two ends of the conductor.

📐Formulae

ΔT=Thot−Tcold\Delta T = T_{hot} - T_{cold}

Q=mcΔTQ = m c \Delta T

Rate of Heat Flow∝ΔT\text{Rate of Heat Flow} \propto \Delta T

H=ΔQΔtH = \frac{\Delta Q}{\Delta t}

💡Examples

Problem 1:

A scientist measures the temperature at one end of a copper rod to be 95∘C95^{\circ}C and the other end to be 22∘C22^{\circ}C. Calculate the temperature difference (ΔT\Delta T) driving the conduction of heat.

Solution:

ΔT=95∘C−22∘C=73∘C\Delta T = 95^{\circ}C - 22^{\circ}C = 73^{\circ}C

Explanation:

Heat flows due to the temperature gradient. The difference between the hot end and the cold end is 73∘C73^{\circ}C.

Problem 2:

Why does a metal spoon feel colder to the touch than a wooden spoon when both are kept in a room at 10∘C10^{\circ}C?

Solution:

The metal spoon is a better conductor of heat than the wooden spoon.

Explanation:

Since metal is a good conductor, it quickly conducts heat away from your finger (which is at a higher temperature, approx 37∘C37^{\circ}C) compared to wood, making the metal feel colder.

Problem 3:

Calculate the total heat energy (QQ) required to raise the temperature of a 2 kg2\text{ kg} metal block if the specific heat capacity cc is 400 J/kg∘C400\text{ J/kg}^{\circ}C and the temperature increase ΔT\Delta T is 10∘C10^{\circ}C.

Solution:

Q=2×400×10=8000 JQ = 2 \times 400 \times 10 = 8000\text{ J}

Explanation:

Using the formula Q=mcΔTQ = m c \Delta T, we multiply the mass, specific heat, and temperature change to find the total heat energy.