Worksheet.Activate Event (Excel)
Occurs when a workbook, worksheet, chart sheet, or embedded chart is activated.
A variable that represents a Worksheet object.
This event doesn't occur when you create a new window.
When you switch between two windows showing the same workbook, the WindowActivate event occurs, but the Activate event for the workbook doesn't occur.
This example sorts the range A1:A10 when the worksheet is activated.
Private Sub Worksheet_Activate()
Range("a1:a10").Sort Key1:=Range("a1"), Order:=xlAscending