# Fields

This site is intended for exploring gravitational and electrical field concepts, particularly when presenting in front of a group with a projected screen or interactive whiteboard, or in a remote teaching situation by sharing the screen.

##### g-Field Page

Explore the gravitational field around Earth in two dimensions by moving a test mass about in the field.

The "Test mass" button toggles a small test mass off/on.  The test mass can be dragged around the field using a mouse or touch.  The magenta vector shows the relative size and direction of the gravitational field at the test mass location.  The vector is not shown if the test mass moves inside the Earth's radius, as it is not meaningful in the context of this demonstration.

When the test mass is visible, a "Mark point" button will mark the g-field at the test mass location by leaving a vector arrow at that location.  This allows marking of several points in the field for comparison.  The "Clear points" button will remove all marked points, as will toggling the test mass off.

The "Vector field" button toggles a representation of the gravitational field off/on.  In this view, the strength of the field is represented by the opacity of the arrows.  The bolder the colour, the larger the field magnitude at that point.

The "Field lines" button toggles field lines on/off.

Resizing the browser window will reset everything to its original state.

##### E-Field 1 Page

Explore the electrical field around a single charge in two dimensions by moving a test charge about in the field.

Three "Test Charge" buttons allow you to select a positive or negative test charge, or to remove the test charge.  The test charge can be dragged around the field using a mouse or touch.  Since the same e-field will push positive and negative test charges in opposite directions, the magenta vector shows the relative size and direction of the force acting on the test charge at that location, not the field direction.  The vector is not shown if the test charge moves inside the central charge's radius, as it is not meaningful in the context of this demonstration.

When the test charge is visible, a "Mark point" button will mark the force at the test charge location by leaving a vector arrow at that location.  This allows marking of several points in the field for comparison.  The "Clear points" button will remove all marked points, as will removing the test charge.

The "Vector field" button toggles a representation of the electric field off/on, where the strength of the field is represented by the opacity of the arrows.  The bolder the colour, the larger the field magnitude at that point.

The "Field lines" button toggles field lines on/off.

Both the vector field and the field lines follow the accepted convention of showing the direction of an e-field as the direction it will push a positive test charge.

Resizing the browser window will reset everything to its original state.

##### E-Field 2 Page

This is similar to the E-Field 1 page, but allows exploration of the field created by two central charges, equal in magnitude.

Both the test charge and the central charges can be switched between positive and negative.  The magnitudes of the charges are fixed.

The arrow shows the direction of the force acting on the test charge, not the field at the charge's location.  The vector field and field lines follow the convention of showing the direction of an e-field as the direction it will push a positive test charge.

The "Fixed in place / Free to move" button will release the test charge so that it moves under the influence of the field.  This can be useful for addressing a common misconception that charges move in the direction of the field lines.

It is not possible to mark test charge locations on this page.