diff --git a/js/ohms-law/view/ControlPanel.js b/js/ohms-law/view/ControlPanel.js
index eef4f4f..dff8950 100644
--- a/js/ohms-law/view/ControlPanel.js
+++ b/js/ohms-law/view/ControlPanel.js
@@ -14,6 +14,7 @@ define( require => {
   const HBox = require( 'SCENERY/nodes/HBox' );
   const inherit = require( 'PHET_CORE/inherit' );
   const MathSymbols = require( 'SCENERY_PHET/MathSymbols' );
+  const merge = require( 'PHET_CORE/merge' );
   const ohmsLaw = require( 'OHMS_LAW/ohmsLaw' );
   const OhmsLawA11yStrings = require( 'OHMS_LAW/ohms-law/OhmsLawA11yStrings' );
   const OhmsLawConstants = require( 'OHMS_LAW/ohms-law/OhmsLawConstants' );
@@ -22,8 +23,8 @@ define( require => {
   const SliderUnit = require( 'OHMS_LAW/ohms-law/view/SliderUnit' );
   const StringUtils = require( 'PHETCOMMON/util/StringUtils' );
   const Util = require( 'DOT/Util' );
-  const ValueChangeUtterance = require( 'SCENERY_PHET/accessibility/ValueChangeUtterance' );
   const utteranceQueue = require( 'SCENERY_PHET/accessibility/utteranceQueue' );
+  const ValueChangeUtterance = require( 'SCENERY_PHET/accessibility/ValueChangeUtterance' );
 
   // strings
   const resistanceString = require( 'string!OHMS_LAW/resistance' );
@@ -62,7 +63,7 @@ define( require => {
 
     const self = this;
 
-    options = _.extend( {
+    options = merge( {
       xMargin: 30,
       yMargin: 10,
       lineWidth: 3,
diff --git a/js/ohms-law/view/CurrentSoundGenerator.js b/js/ohms-law/view/CurrentSoundGenerator.js
index 2426b62..fd68b7a 100644
--- a/js/ohms-law/view/CurrentSoundGenerator.js
+++ b/js/ohms-law/view/CurrentSoundGenerator.js
@@ -11,6 +11,7 @@ define( require => {
   'use strict';
 
   // modules
+  const merge = require( 'PHET_CORE/merge' );
   const ohmsLaw = require( 'OHMS_LAW/ohmsLaw' );
   const OhmsLawConstants = require( 'OHMS_LAW/ohms-law/OhmsLawConstants' );
   const SoundClip = require( 'TAMBO/sound-generators/SoundClip' );
@@ -31,7 +32,7 @@ define( require => {
      */
     constructor( currentProperty, options ) {
 
-      options = _.extend( {
+      options = merge( {
         initialOutputLevel: 1
       }, options );
       options.loop = true; // must be a loop to work properly
diff --git a/js/ohms-law/view/FormulaNode.js b/js/ohms-law/view/FormulaNode.js
index 3d42cd6..9a5562e 100644
--- a/js/ohms-law/view/FormulaNode.js
+++ b/js/ohms-law/view/FormulaNode.js
@@ -12,6 +12,7 @@ define( require => {
   // modules
   const inherit = require( 'PHET_CORE/inherit' );
   const MathSymbols = require( 'SCENERY_PHET/MathSymbols' );
+  const merge = require( 'PHET_CORE/merge' );
   const Node = require( 'SCENERY/nodes/Node' );
   const ohmsLaw = require( 'OHMS_LAW/ohmsLaw' );
   const OhmsLawA11yStrings = require( 'OHMS_LAW/ohms-law/OhmsLawA11yStrings' );
@@ -48,7 +49,7 @@ define( require => {
    */
   function FormulaNode( model, tandem, options ) {
 
-    options = _.extend( {
+    options = merge( {
 
       // a11y
       labelContent: ohmsLawEquationString,
diff --git a/js/ohms-law/view/ReadoutPanel.js b/js/ohms-law/view/ReadoutPanel.js
index 647bffe..92a1261 100644
--- a/js/ohms-law/view/ReadoutPanel.js
+++ b/js/ohms-law/view/ReadoutPanel.js
@@ -11,6 +11,7 @@ define( require => {
   // modules
   const HBox = require( 'SCENERY/nodes/HBox' );
   const inherit = require( 'PHET_CORE/inherit' );
+  const merge = require( 'PHET_CORE/merge' );
   const ohmsLaw = require( 'OHMS_LAW/ohmsLaw' );
   const OhmsLawConstants = require( 'OHMS_LAW/ohms-law/OhmsLawConstants' );
   const OhmsLawModel = require( 'OHMS_LAW/ohms-law/model/OhmsLawModel' );
@@ -38,7 +39,7 @@ define( require => {
   function ReadoutPanel( model, tandem, options ) {
 
     assert && assert( !options.tandem, 'Tandem should be supplied as a parameter' );
-    options = _.extend( {
+    options = merge( {
       xMargin: 30,
       yMargin: 8,
       lineWidth: 3,
diff --git a/js/ohms-law/view/ResistorNode.js b/js/ohms-law/view/ResistorNode.js
index 5f60d8b..7f92fe1 100644
--- a/js/ohms-law/view/ResistorNode.js
+++ b/js/ohms-law/view/ResistorNode.js
@@ -13,6 +13,7 @@ define( require => {
   const inherit = require( 'PHET_CORE/inherit' );
   const LinearFunction = require( 'DOT/LinearFunction' );
   const LinearGradient = require( 'SCENERY/util/LinearGradient' );
+  const merge = require( 'PHET_CORE/merge' );
   const Node = require( 'SCENERY/nodes/Node' );
   const ohmsLaw = require( 'OHMS_LAW/ohmsLaw' );
   const OhmsLawA11yStrings = require( 'OHMS_LAW/ohms-law/OhmsLawA11yStrings' );
@@ -73,7 +74,7 @@ define( require => {
    */
   function ResistorNode( resistanceProperty, tandem, options ) {
 
-    options = _.extend( {
+    options = merge( {
 
       // a11y
       tagName: 'li' // this assumes that it is a child of a 'ul'
diff --git a/js/ohms-law/view/WireBox.js b/js/ohms-law/view/WireBox.js
index 57a865b..968f6db 100644
--- a/js/ohms-law/view/WireBox.js
+++ b/js/ohms-law/view/WireBox.js
@@ -11,6 +11,7 @@ define( require => {
   // modules
   const BatteriesView = require( 'OHMS_LAW/ohms-law/view/BatteriesView' );
   const inherit = require( 'PHET_CORE/inherit' );
+  const merge = require( 'PHET_CORE/merge' );
   const Node = require( 'SCENERY/nodes/Node' );
   const ohmsLaw = require( 'OHMS_LAW/ohmsLaw' );
   const OhmsLawA11yStrings = require( 'OHMS_LAW/ohms-law/OhmsLawA11yStrings' );
@@ -41,7 +42,7 @@ define( require => {
    */
   function WireBox( model, tandem, options ) {
 
-    options = _.extend( {
+    options = merge( {
 
       // phet-io
       tandem: tandem,