When a copper plate with a hole is heated, it expands uniformly in all directions due to thermal expansion. The hole behaves as if it were made of copper itself. The diameter of the hole is a linear dimension, and it increases with temperature, just like the outer dimensions of the plate. The change in diameter (ΔD) is given by ΔD = D₀ * α * ΔT, where D₀ is the original diameter, α is the coefficient of linear expansion, and ΔT is the temperature change.

Therefore, the diameter of the hole will always increase.

Final Answer: always increase