Explain linear expansivity and solve a problem involving the difference in length of brass and iron rods when heated.

Here are the solutions to your questions:

9 (a) (i)
Explain linear expansivity.

Linear expansivity is the fractional increase in length per unit rise in temperature of a substance. It is a material property that describes how much a material expands or contracts in length for each degree Celsius or Kelvin change in temperature.

9 (a) (ii)
A brass rod and an iron rod differ in length by $24 \text{ cm}$ at $20^\circ \text{C}$. What should be the original length of the iron rod for the difference in length to remain the same when both rods are heated to $90^\circ \text{C}$?
Linear expansivity of brass = $1.9 \times 1