code to generate serial number based on number of records

I have a data in Sheet1 with few records as mentioned below. I want the result in sheet2 with column "A" serial number (number should start from A2 and should be equal to the number of records in Sheet1 (Excluding heading) Example given below. I will be adding the records in sheet2 from time to time.

DATA

Sheet1
"A"
Name (Heading)
Sam
Lucas
Wilfred
Anthony
Josephine

RESULT NEEDED

Sheet2
"A" | "B"
Sr No. | Name
1 | Sam
2 | Lucas
3 | Wilfred
4 | Anthony
5 | Josephine

In sheet 2
A2 B2
=IF(B2<>"",ROW()-1,"") =IF(Sheet1!A2<>"",Sheet1!A2,"")

and drag down

Thank you very much for the code. But I want VBA to drag it automatically in sheet2 till the end of record available in sheet1.

Because I want to use the same in more than 20 sheets. So every time dragging manually is bit lengthy process