Admob with android app

Question

i tried to integrate admob with android app but its working fine in enumulator but not with real time device 

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

xmlns:ads="http://schemas.android.com/apk/res-auto"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

tools:context="com.example.android_addmob_ads.MainActivity" >

<TextView

android:id="@+id/textView1"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="@string/hello_world" />

<com.google.android.gms.ads.AdView android:id="@+id/adView"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

ads:adUnitId="ca-app-pub-xyz"

ads:adSize="BANNER"/>

</RelativeLayout>

AdView adView = (AdView)this.findViewById(R.id.adView);

AdRequest adRequest = new AdRequest.Builder().build();

adView.loadAd(adRequest);