What is thermal expansion?
The increase in size or volume of a substance when heat is applied.
Give two uses of thermal expansion.
Riveting metal plates and constructing fire alarms or electric irons.
State one disadvantage of thermal expansion.
It can deform bridge structures or cause railway tracks to buckle.
Define linear expansivity \( \alpha \).
The fractional increase in length per unit length per degree rise in temperature.
Give the formula for linear expansivity.
\( \alpha = \frac{l_2 - l_1}{l_1 (\theta_2 - \theta_1)} \)
What is area expansivity \( \beta \)?
The fractional increase in area per unit area per degree rise in temperature.
State the relation between area and linear expansivity.
\( \beta = 2\alpha \)
Give the formula for area expansivity.
\( \beta = \frac{A_2 - A_1}{A_1 (\theta_2 - \theta_1)} \)
Define volume or cubical expansivity \( \gamma \).
The fractional increase in volume per unit volume per degree rise in temperature.
Give the formula for volume expansivity.
\( \gamma = \frac{V_2 - V_1}{V_1 (\theta_2 - \theta_1)} \)
State the relationship between volume and linear expansivity.
\( \gamma = 3\alpha \)
What is apparent cubic expansivity \( \gamma_a \)?
The observed increase in volume of a liquid in a container, ignoring the container's expansion.
Give a formula for apparent expansivity using volume.
\( \gamma_a = \frac{\Delta V_{\text{apparent}}}{V \Delta \theta} \)
Give a formula for apparent expansivity using mass.
\( \gamma_a = \frac{\text{mass of liquid expelled}}{\text{mass of liquid remaining} \times \Delta \theta} \)
What is real or absolute expansivity \( \gamma_r \)?
The true expansion of a liquid after accounting for the container's expansion.
Give the relation between real and apparent expansivity.
\( \gamma_r = \gamma_a + \gamma_c \)
What does \( \gamma_c \) represent?
The cubic expansivity of the container or vessel.
Why do thick glasses crack when heated unevenly?
Uneven expansion causes internal stress leading to cracks.
What unit is used to express expansivity?
Per kelvin, \( \text{K}^{-1} \)
Why must bridges have expansion joints?
To allow expansion and prevent structural damage due to thermal expansion.
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