LEARNATHON

III

Competition for grade 6 to 10 students! Learn, solve tests and earn prizes!

Learn more### Theory:

You may have noticed that the land is cool in the mornings and hot in the afternoons. However, the water in a lake will be almost at the same temperature in the morning as well as in the afternoon. Both are exposed to the same amount of solar heat energy, but they react in different ways. It's because their properties are so dissimilar. Three factors determine the amount of heat energy absorbed or lost by a body in general.

- Mass of the body
- Change in temperature of the body
- Nature of the material of the body

We can understand this from the following observations.

**Observation 1**:

The amount of heat needed to raise the temperature of \(1\) litre of water is greater than the amount needed to raise the temperature of \(500\) \(ml\) of water. If \(Q\) denotes the amount of heat absorbed and m denotes the body's mass, then

$Q\propto m$

**Observation 2**:

The amount of heat energy (Q) required to bring \(250\) \(mL\) of water to \(100°C\) is greater than the amount of heat energy required to bring the temperature to \(50°C\). Here,

$Q\propto \mathrm{\Delta}T$,

where

\(ΔT\) \(-\) Change in temperature of the body.

Thus, heat lost or gained by a substance when its temperature changes by \(ΔT\) is,

$\begin{array}{l}Q\propto m\mathrm{\Delta}T\\ Q=\mathit{mC}\mathrm{\Delta}T\end{array}$

The absolute temperature and energy of a system are proportional to each other, according to the above equations. The proportionality constant is the substance's specific heat capacity (C).

$C=\frac{Q}{m\mathrm{\Delta}T}$

As a result, a substance's specific heat capacity is defined as the amount of heat required to raise the temperature of 1 kg of the substance by 10 degrees Celsius or 1 degree Kelvin. $J{\mathit{kg}}^{-1}{K}^{-1}$ is the unit of specific heat capacity. \(J/kg°C\) and \(J/g°C\) are the most commonly used units of specific heat capacity.

Water has the highest specific heat capacity of all the substances, with a value of \(4200 J/kg°K\). As a result, water absorbs a significant amount of heat per unit increase in temperature. To keep engines and other machinery parts cool, water is used as a coolant in car radiators and factories. The temperature of the water in the lake does not change much during the day due to the same reason.

Specific heat capacity of various substances.

S.no | Substance | Specific heat capacity($J{\mathit{kg}}^{-1}{K}^{-1}$) |

1. | Lead | \(130\) |

2. | Mercury | \(139\) |

3. | Brass | \(380\) |

4. | Zinc | \(391\) |

5. | Copper | \(399\) |

6. | Iron | \(483\) |

7. | Glass | \(504\) |

8. | Aluminium | \(882\) |

9. | Kerosene | \(2100\) |

10. | Ice | \(2100\) |

11. | Sea water | \(3900\) |

12. | water | \(4180\) |