Millikan's Basement

Choose a mode along the top: Beam line, Mystery particle or Millikan.
On the Beam line, choose a Particle under the apparatus.
Set each value on its module: turn the knob, or tap the display and type.
Press FIRE. The path is drawn in slow motion and the numbers appear in the Data panel.
When you are ready, turn on Predict and try a challenge.

Knobs: drag round. The scroll wheel over a knob or display also steps the value.
Displays: tap to type. Enter confirms, Esc cancels, and tapping anywhere else confirms. The amber box is the edit box.
Small chips on a module flip a polarity or the direction of B. Plates, B field and Screen under the apparatus switch each part on or off.
+, − and ⤢ zoom in, zoom out and fit the view. Ctrl + scroll also zooms. When zoomed in, drag to pan.
The controls are locked while Predict is on.
Rebuild the bench (below) runs the first-visit tour again: the bench starts bare and you place each piece of equipment yourself. In the Millikan room it rebuilds the oil-drop apparatus.

A charge is accelerated from rest through V_acc, passes between plates (separation d, length L, plate p.d. V_p), can cross a magnetic field region, and lands on a screen a distance D beyond the plates.
The colour key in the Data panel shows d, L, D and y. y is measured from the centre line, with up positive.
Display options: Time dots, v components, Force arrow and Right-hand rule.

Turn on Predict, choose a challenge, and type a value with its unit, or choose an answer.
Press Lock in prediction, then FIRE. The tolerance can be set from ±1 % to ±10 %.
The worked solution is shown afterwards, even when you are right, because a right answer can be a lucky guess.
Download log (CSV) saves your challenge log.

A guided investigation, as practice for an IA: find q/m for an unknown particle and identify it.
Each question must be attempted before the next one opens.
For each value of B, press FIRE, read s on the magnified ruler, type it and press Record. Take 3 trials at 5 or more values of B.
Open in SGL sends your table to the SGL graphing tool, set up to plot s against 1/B with max/min lines.
Your progress is saved in this browser. Download my answers saves them to hand in.

Press SPRAY, tap a drop in the eyepiece, then press Start a record.
Field OFF: time the drop falling a number of graticule divisions (1 division = 0.100 mm).
Field ON: set V so the drop rises steadily. If it falls faster instead, press POL. If it never rises, it is uncharged: choose another drop.
Find r from the falling speed, q from the rising speed and n = q / e, then press Check.

The Data panel lists the values for the last shot: exit speed, kinetic energy, the deflection between the plates, the motion in the field and the spot on the screen.
Results go to SGL through a link that keeps every value exactly as you typed it, with its uncertainty. Strict precision is on, so values must match the decimal places of their uncertainty.

Right and up are positive, so left and down are negative. g = −9.81 m s⁻².
Worked solutions show the equation, the rearrangement until the variable is isolated, the substitution, and a step-by-step evaluation.
Table headings are in IB style, for example s / cm ± 0.05.

In the mystery lab, V and B fluctuate slightly from shot to shot, and you judge the centre of the spot on the ruler yourself.
Oil drops wander because of Brownian motion (it can be switched off), and you start and stop the stopwatch by hand.
Scatter between trials is expected. Explaining it is part of the experiment.