SQL query execution timings

Question

I am not getting the reason why query 1 is taking 10 seconds,query 2 and query 3 taking 1 second to execute even if they are same only order is different

 

1.SELECT TOP 10000 * FROM tbl1

WHERE

len(empid) = 4 and

isnumeric(empid) = 1   ORDER BY empid desc

2.SELECT TOP 10000 * FROM tbl1

WHERE

len(Employee_ID) = 4 and

isnumeric(empid) = 1 

 

3.SELECT TOP 10000 * FROM tbl1

WHERE

len(empid) = 4 and

isnumeric(empid) = 1 ORDER BY empid