Purpose
This interactive provides three-dimensional animated view of the effects of a uniform magnetic field on a moving charge.

Using the Interactive
Configure the interactive using the FIELD CONTROLS template on the right-hand side.

• The blue lines indicate the line along which the magnetic field is oriented.
• The red ball is the charged particle. It is always red regardless of the sign of its charge.
• The three arrows show the directions of the velocity (red), magnetic field (blue), and acceleration (green).
• The black circles indicate the region in which the magnetic field is contained if that feature is selected (see below).
• To orient your view click TOP or SIDE at the bottom right, or drag your mouse anywhere in the scene.

The Controls

• Use the slider bars to alter the STRENGTH of the magnetic field, CHARGE on the particle, the particle's MASS, the magnitude of the particle's VELOCITY, and the ANGLE of the particle's velocity with respect to the horizontal.
• Select INFINITE and the field fills all of space; select CONTAINED and the field is confined to within the black circles.
• Play begins the animation of the particle's motion.
• Select FOCUS VIEW ON PARTICLE to fix the particle in the center. That is, you are in the particle's rest frame.

1			Drag your mouse (slightly down and left works well) so that the directions of all three vectors are visible. Note the sign of the charge and verify that the vectors are consistent with the right-hand rule. What will happen if you increase the magnitude of the charge?
			A)	Only the acceleration vector will get longer.
			B)	Only the acceleration vector will get shorter.
			C)	Both the velocity and acceleration vectors will get longer.
			D)	Both the velocity and acceleration vectors will get shorter.
			E)	Everything will stay the same.
2			What will happen if you make the charge positive and increase the magnitude?
			A)	Only the acceleration vector will get longer, in the opposite direction as before.
			B)	Only the acceleration vector will get longer, in the same direction as before.
			C)	The acceleration will remain zero.
3			What will happen if you decrease the magnitude of the magnetic field?
			A)	Only the acceleration vector will get longer.
			B)	Only the acceleration vector will get shorter.
			C)	Only the magnetic field vector will get shorter.
			D)	Only the magnetic field vector will get longer.
			E)	Both the magnetic field and acceleration vectors will get longer.
			F)	Both the magnetic field and acceleration vectors will get shorter.
4			What will happen if you increase the magnitude of the magnetic field in the opposite direction from before?
			A)	Both the magnetic field and acceleration vectors will get longer in the same directions as before.
			B)	The magnetic field will get longer in the opposite direction as before while the acceleration will get longer in the same direction as before.
			C)	Both the magnetic field and acceleration vectors will get longer in the opposite directions as before.
			D)	Both the magnetic field and acceleration vectors will get longer in the opposite directions as before while the velocity vector also reverses direction.
5			Given the present situation (of charge, field, and velocity), describe the motion of the particle?
			A)	The charge will move in a circular path, clockwise as viewed from above.
			B)	The charge will move in a circular path, counterclockwise as viewed from above.
			C)	The charge will move in an elliptical path, clockwise as viewed from above.
			D)	The charge will move in an elliptical path, counterclockwise as viewed from above.
			E)	The charge will move in an helical path, spiraling along the direction of the magnetic field.
			F)	The charge will move in an helical path, spiraling in the opposite direction of the magnetic field.