DIRECTIONS

Directions for using the software

In this software after pressing CONTINUE appears a simulation of the experiment proposed by Alan Van Heuvelen in Physics Teacher (1999)

FIRST PART: EXPLANATION OF THE SHAPE OF VOLTAGE VS. TIME IN TERMS OF MONOPOLES

PARAMTERES THAT WE CAN CHANGE IN THE FORM CHANGING THE PARAMETERS:

Solenoid (coil): Length, number of turns, radius

Magnet: Length, initial position

Curve: Angle with horizontal plane, a factor that determines the shape to be more like a classic hyperbola

Right End: We can move the end of movement of the magnet, where it comes back.

CHOICES:

A) MENU BAR OF CHANGING THE PARAMETERS

REPEAT: Calculates the voltages for a single passing of the magnet through the coil.

TIME: We observe the temporal evolution of the experiment. Vectors representing the velocities appear.

STOP: Stops the timer.

STEP: We observe the movement of the magnet step by step

GRAPHICAL REPRESENTATION

Graph with adjustable scale: Depending on the number of turns and speed the scale is adjusted. Apperas a form with the title VOLTAGE TIME. Some of the graphs are not very accurate as a compormise to speed of calculations. More accuracy is on choosing the MONOPOLES VS VOLTAGE (see below).

Graph with constant scale: This helps the student appreciate the voltage in terms of the initial choice. Appears in the form CONSTANT SCALE

EXPALANATION WITH MONOPOLES

Movement of monopole: In the form "VOLTAGE TIME" appears the total voltage as a combination of the voltages induced by two monopoles. A DRAWBACK: THE USER MUST WAIT TO FINISH THE PASSING THROUGH THE MAGNET.

Flux of a monopole: The flux as a function of position (or of time because the monopole is considered as moving with a constant speed) of a north pole: By pressing the menu item appears a form with two buttons:

Α)Motion to explain the curve: Appears a pole moving through a loop. It will be evident that the flux increases as the pole approaches the loop, but it changes sign and the flux get a negative value (equal in size to the value just before the crossing of the loop).

Β)Rate of change of flux: Gives the rate of change of flux for a the movement of the monopole. It is an important point for dealing with the difficulties connected with the negative flux after the crossing. Usually the students insist that the rate is negative because the values of the flux are negative!

Voltage induced by the monopole: It allows the observation of the voltage that appears in the ends of a coil as the superposition of the voltage due to the north pole and the voltage due to the south pole. The curve corresponds to a constant speed 4,5. To study a bigger part of the curve a bigger value of the velocity must be chosen, and to study in more detail the curve a smaller velocity must be chosen. By changing the number of turns, or the length of the magnet, or/ and the coil's length one can study the influence of these parameters to the shape of the curve.

SECOND PART: MOVEMENT OF A MAGNET AND A LOOP

This part starts by pressing the menu item LEN'S FORCE

In this second part the movement of a magnet through a loop can be studied.

The following parameters can be changed:

A) Length of a magnet (choose a long magnet so that the effects will be more prominent)

B) Magnet's mass (choose a small mass for more intense changes)

C) Initial speed of the magnet

D) Resistance of the coil.

E) Coil's mass

F) Position of the coil

G) Radius of the coil

There are the following buttons in the form "LENZ'S FORCES"

MOVEMENT, STEP, STOP, ERASE, BACK, and in a different color the following:FALL IN A COIL, FALL IN INDEPENDENT LOOPS, FALL IN A PIPE

MOVEMENT: The magnet starts and appear the following graphs: positions of magnet, coil and center of mass vs. time, speed of magnet, coil and center of mass vs. time. It can be observed that the center of mass has a constant speed over time. By choosing different parameters it can be achieved that the magnet and coil move with same final speed. There can also appear two decelerations: One upon the entrance of the magnet in the loop and one in the exit from the loop.

THIRD PART: FALL OF A MAGNET IN A LOOP

We keep the same choices of number of turns from the first form (CHANGING THE PARAMETERS)and the choices of length and mass of the magnet as also the resistance of the coil from the form LENZ'S FORCE).

3 BUTTONS IN LENZ'S FORCE: Fall in a coil, fall in independent loops and fall in a pipe.

By pressing one of these buttons appears the form FALL IN A COIL OR PIPE

ATTENTION: TO HAVE QUICK RESULTS FOR A COIL OR A SET OF INDEPENDENT LOOPS, THE NUMBER OF TURNS (from form CHANGING THE PARAMETERS) SHOULD BE KEPT LOW (FOR EXAMPLE <20)

GRAPHS
Α) Speed vs. time

Appears the graph of speed (appears a final velocity - inside the coil -for certain values of the parameters) and for comparison the speed of free fall.

Β) Position vs. time

Similarly appears the position vs. time and the position of a body that falls freely. With red lines appear the positions of the loops.

C) Acceleration vs. time

For free fall a =g. For a loop or a coil appear peaks. For a pipe appears a continues curve.

Attention: FOR FALL IN A PIPE THE LENGTH OF THE MAGNET SHOULD BE KEPT THE MINIMUM POSSIBLE (d _MAGNET =1) because the calculation were approximate to get quick results