How to limit a ray to go downwards to infinity, how can I make it down only 1 float.

I have a character with a rigidbody, that casts a ray downwards, I want the ray to go downwards just one unit. This is the code.

using UnityEngine; using System.Collections;

public class TP_Controller : MonoBehaviour { public static Rigidbody Rigidbody2; public static TP_Controller Instance;

 RaycastHit hit;
 float dist;
 Vector3 dir;
 public bool isgrounded;
 

 void Awake () // Debe quedarse en awake
 {

     Rigidbody2 = GetComponent("Rigidbody") as Rigidbody;
     Instance = this;

 }
 

 void Update () 
 {
     if (Camera.mainCamera == null)
         return;

     GetLocomotionInput();

     TP_Motor.Instance.UpdateMotor();

     dist = 10;
     dir = new Vector3(0,-1,0);

     Debug.DrawRay(transform.position, dir * dist, Color.green);
 }

 void IsGrounded()
 {

     if(Physics.Raycast(Rigidbody2.transform.position, dir, out hit, dist)) // This must be edited
     
     {
         isgrounded = false; // Debe mantenerse en true
      }
 }