An example of a somewhat complicated way of loading jQuery. Why not simply declare jQuery as a dependency and let WordPress manage the version of jQuery that is used?

trickyjQ.php

<?php
// start with setting some defaults

/**
 * Set defaults
 */
function squelch_taas_set_defaults() {
    // Default versions of external scripts
    $jquery_ver     = '1.9.1';
    $jquery_ui_ver  = '1.10.2';

    // Show welcme message
    update_option( 'squelch_taas_showmessage', 2 );

    // Default options
    set_default_option( 'squelch_taas_jquery_ui_theme',         'smoothness'    );
    set_default_option( 'squelch_taas_jquery_ver',              $jquery_ver     );
    set_default_option( 'squelch_taas_jquery_ui_ver',           $jquery_ui_ver  );
    update_option(      'squelch_taas_load_jquery',             true            );
    update_option(      'squelch_taas_load_jquery_ui',          true            );

    // Has the user set their own jQuery / jQuery UI versions?
    $update_jquery      = (get_option('squelch_taas_jquery_ver')    == get_option('squelch_taas_jquery_ver_default')    );
    $update_jquery_ui   = (get_option('squelch_taas_jquery_ui_ver') == get_option('squelch_taas_jquery_ui_ver_default') );

    if ($update_jquery)     error_log( "Going to update jquery ver");
    else                    error_log( 'jquery ver: '.get_option( 'squelch_taas_jquery_ver') );
    if ($update_jquery_ui)  error_log( "Going to update jquery ui ver");
    else                    error_log( 'jquery UI ver: '.get_option( 'squelch_taas_jquery_ui_ver') );

    update_option(      'squelch_taas_jquery_ver_default',      $jquery_ver     );
    update_option(      'squelch_taas_jquery_ui_ver_default',   $jquery_ui_ver  );

    // On upgrade, bump the version of jquery loaded UNLESS the user has overridden the versions in the config, in which case warn them
    if ($update_jquery)     update_option( 'squelch_taas_jquery_ver',       $jquery_ver     );
    else                    update_option( 'squelch_taas_upgrade_warning',  1               );
    if ($update_jquery_ui)  update_option( 'squelch_taas_jquery_ui_ver',    $jquery_ui_ver  );
    else                    update_option( 'squelch_taas_upgrade_warning',  1 );
}

// [...]   

//  set up some detection and warning messages if someone changes the default settings to load a different version of jQuery

    if ( get_option( 'squelch_taas_upgrade_warning' ) > 0 ) {
        $url        = squelch_taas_get_plugin_admin_url();
        $url_rmv    = $url.'&taas-rmvmsg=upgrade_warning';


        $update_jquery          = !(get_option('squelch_taas_jquery_ver')    == get_option( 'squelch_taas_jquery_ver_default'    ));
        $update_jquery_ui       = !(get_option('squelch_taas_jquery_ui_ver') == get_option( 'squelch_taas_jquery_ui_ver_default' ));

        if ($update_jquery || $update_jquery_ui) {
            $jquery_ver             = get_option( 'squelch_taas_jquery_ver'             );
            $jquery_ui_ver          = get_option( 'squelch_taas_jquery_ui_ver'          );
            $jquery_ver_default     = get_option( 'squelch_taas_jquery_ver_default'     );
            $jquery_ui_ver_default  = get_option( 'squelch_taas_jquery_ui_ver_default'  );

            $msg  = '<div class="error">'
                .'<p>'
                .'You have configured Squelch Tabs and Accordions Shortcodes to load ';
            if ($update_jquery && $update_jquery_ui)        $msg .= 'version '.$jquery_ver.' of jQuery and version '.$jquery_ui_ver.' of jQuery UI ';
            else if (!$update_jquery && $update_jquery_ui)  $msg .= 'version '.$jquery_ui_ver.' of jQuery UI ';
            else                                            $msg .= 'version '.$jquery_ver.' of jQuery ';
            $msg .= ''
                .'on your website, but the recommended ';
            if ($update_jquery && $update_jquery_ui)        $msg .= 'versions are now '.$jquery_ver_default.' and '.$jquery_ui_ver_default.'. ';
            else if (!$update_jquery && $update_jquery_ui)  $msg .= 'version is now '.$jquery_ui_ver_default.'. ';
            else                                            $msg .= 'version is now '.$jquery_ver_default.'. ';
            $msg .= ''
                .'It is highly recommended that you update your settings to the new versions on the '
                .'<a href="'.$url.'">settings</a> page. '
                .'<a href="'.$url_rmv.'">Remove this message</a></p></div>';
            echo $msg;
        }
    }
    
    
// [...]    

// deregister the WP bundled copy of jQuery and "hard-wire the plugin to specific versions to prevent incompatibility problems"     
/**
 * Enqueue the JavaScript and CSS.
 */
function squelch_taas_enqueue_scripts() {
    global $taas_plugin_ver;

    $load_jquery    = get_option('squelch_taas_load_jquery');
    $jquery_ver     = get_option('squelch_taas_jquery_ver');
    $load_jquery_ui = get_option('squelch_taas_load_jquery_ui');
    $jquery_ui_ver  = get_option('squelch_taas_jquery_ui_ver');

    $protocol = (!empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] !== 'off' || $_SERVER['SERVER_PORT'] == 443) ? "https:" : "http:";

    // Piggyback the Google APIs CDN but hard-wire the plugin to specific versions to prevent incompatibility problems
    if ($load_jquery) {
        wp_deregister_script( 'jquery' );
        wp_register_script(   'jquery', $protocol.'//ajax.googleapis.com/ajax/libs/jquery/'.$jquery_ver.'/jquery.min.js' );
        wp_enqueue_script(    'jquery' );
    }

    if ($load_jquery_ui) {
        wp_deregister_script( 'jquery-ui-core' );
        wp_register_script(   'jquery-ui-core', $protocol.'//ajax.googleapis.com/ajax/libs/jqueryui/'.$jquery_ui_ver.'/jquery-ui.min.js' );
        wp_enqueue_script(    'jquery-ui-core' );
    }

    // Enqueue the JavaScript
    wp_enqueue_script(
        'squelch_taas',
        plugins_url( 'js/squelch-tabs-and-accordions.js', __FILE__ ),
        array( 'jquery', 'jquery-ui-core' ),
        $taas_plugin_ver,
        true
    );