Electric field patterns sim
Switch on an EHT supply joined to electrodes in a dish of castor oil and watch semolina grains line up into the field pattern of a point, a charged sphere, two points or two parallel plates; drag the electrodes, show field lines running from + to −, and drop in a small + or − test charge to see the force on it.
Static electricity: electric fields · covers the O-Level, IGCSE, GCSE topic
What the sim shows
Model (beyond the syllabus): the field in the plane of the oil (two dimensions, as the electrodes stand upright through a thin layer). Each electrode is held at its terminal's voltage (+ at the set voltage, − at 0 V); the field is the sum of the fields of charges spread on the electrodes, their sizes solved so each electrode's surface is at its voltage. A pin (2 mm brass rod) is one line charge, whose field falls as 1 ÷ r (a true point charge's falls as 1 ÷ r²; the pattern's shape is the same). The disc (20 mm across, standing in for a charged sphere), the strips (76 mm "plates") and the ring are cut into short panels. The field is cut at the dish's wall; the oil, glass and air are left out. Grains turn fully into line at 12 kV/m or more, not at all below 4 kV/m (chosen), and never turn back until stirred; they are drawn larger than life. The test charge (±1 nC) is imagined: F = qE, and it does not change the field.
- The voltage knob on the EHT supply (drag it); the electrodes and the test charge drag too
- EHT supply, glass dish of castor oil with semolina grains, brass and copper electrodes, white tile, leads
Use it in your lessons
- Try it here: anyone can unlock 2 figures free, and a free account unlocks up to 5. Runs on a laptop, a Chromebook or a phone; nothing to install.
- Present it and share student links with the teacher plan, from US$5 a month, billed yearly.
- Put it on your own website or LMS for US$9, paid once, or every sim from US$29 a month.
Free guide: 12 practicals as sims, and how to run one in a lesson →
Need a version for your exact set-up? Have one made: US$49 a figure in an order of 5.
More physics sims
- Density: a regular block, an irregular stone and a liquid simMeasure a block with a rule, find a stone's volume by displacement, weigh a liquid in a cylinder, and work out ρ = m ÷ V for each.
- Digital calipers: outside, inside and depth simClose the jaws on a rod, open them in a pipe, push the depth rod into a hole, find and correct the zero error, and choose between a rule, calipers and a micrometer.
- Digital micrometer screw gauge: zero it, then measure a wire simFind and correct a positive or negative zero error, close the jaws on a wire with the ratchet, measure the diameter at three places, average, and work out A = πd²/4.
- EM spectrum explorer: radio waves to gamma rays simDrag a slider along the spectrum on a log scale: λ and f change in opposite directions while c stays 3.0 × 10⁸ m/s, and each band shows its source, detector, uses and dangers.
- Free-body diagram builder simDrag weight, normal contact, tension, friction, air resistance, driving force and push onto a book, a lamp, a box, a parachutist, a lift, a car and two joined blocks; set each size, check the diagram, and see the resultant and the motion it predicts.
- Friction: pulling a block with a newton-meter simPull a block with a newton-meter: friction matches the pull until the block slips, then drops to a smaller sliding friction. Change the surface, oil it, add masses, and plot friction against the normal force.