I have added some fields in schema.xml of core named \"Core3\" created by me in solr v5.1. I am not referring to examples folder but using \"server\" folder to run solr server a
In the solrconfig.xml file in the conf folder located in the directory for your core. There is a way to define using a managed-schema or schema.xml for that core
To use schema.xml it says to set <schemaFactory>
to...
<schemaFactory class="ClassicIndexSchemaFactory"/>
To use the managed-schema file, which seems to be the default when you create a new core in this way (this file is not supposed to be hand edited but rather use the dynamic schema REST API to programmatically edit it) you would set it to...
<schemaFactory class="ManagedIndexSchemaFactory">
<bool name="mutable">true</bool>
<str name="managedSchemaResourceName">managed-schema</str>
</schemaFactory>
More on this can be found here... https://cwiki.apache.org/confluence/display/solr/Managed+Schema+Definition+in+SolrConfig
Or there is explanation in the solrconfig.xml file itself near the schemaFactory section.