Five unknown charges are shown on the screen along with vectors representing the forces on each charge.   Which charges are positive and which ones are negative?  You can click-drag on any charge to change its position.  Start

Five unknown charges are shown on the screen along with vectors representing the forces on each charge.   Which charges have like signs?  You can click-drag on any charge to change its position.  Start

Two fixed charges are shown in black. Drag the small green test charge around the screen and observe how the force vector changes magnitude and direction.  What are the magnitude and sign of the charge on the right if the fixed charge on the left has a value of +4 mC?  Start

A fixed particle is shown in the animation along with a dragable particle having a charge of 1 mC. The vector represents the force on the drag-able particle and the message box displays the magnitude of this force as you drag the particle. The force on the fixed particle is not shown but you know it exists from Newton's third law. Is the force acting between the two particles a Coulomb force?  If so, what is the charge on the fixed particle?   Start

Two like-charged 500 gram spheres attached to rigid rods form an electroscope as shown in the animation (position given in centimeters and time is in seconds). Determine the charge on each sphere. You may drag the spheres to whatever position you wish before or during the animation. You can also damp the motion by clicking the "Damp Velocity" button. Start

One fixed charge and one "test" charge is shown in each animation. In which animation is the "test" charge a true "test" charge?   You can click-drag on the "test" charge to change its position. 

A fixed particle with an unknown charge uniformly distributed about its volume is shown. The vectors shown point in the direction of the electric field and the color of the vectors represent the field's magnitude.  Distance is measured in m.  Determine the charge on the particle in Coulombs and the number of excess electrons that are on the sphere by dragging around the test charge.    Start

Double-click inside the animation to draw a field lines.  Which of the following statements is true. (Note:  Since you may draw as many field lines as you wish,  the number number of field lines will not be proportional to the magnitude of the charge as in the text.)   Start

Two charges are shown in the animation.  Double-click inside the animation to draw field lines and then decide which of the following statements is true.  Start

A  1kg, 1C charge is attached to a massless rigid string subject to the gravitational field of the earth and an electric field that points to the right as shown in the animation (position is in meters and time is in seconds). Determine the strength of the electric field. You may drag the charge and use the damping button to damp out the oscillation.  Start

An electron is fired from an electron gun into an unknown electric field created by two charged plates and is deflected as shown in the animation (position is given in centimeters and time is in seconds). Find the magnitude of the electric field. You may assume that there is no significant effect to to fringing.  Start