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  • New Section Investigates Magnets, Motors and Generators
  • A Hands-on Approach
  • Concepts Develop Intuitively
  • A Complete Curriculum (pdf download) Includes Many New Refinements to Teacher and Student Manuals




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Two versions of this kit are offered:

  • The CASTLE Kit—for two students
  • The Economy CASTLE Kit—for eight students.

 Material Safety Data Sheet

Liquid filled compass
(English – 40 KB –pdf)

 Additional User Resources

Check the User Resources Tab for:

  • MSDS
  • Replacement Parts
  • Manuals
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The CASTLE™ Approach

CASTLE (Capacitor-Aided System for Teaching and Learning Electricity) is a high school electricity curriculum that leads students from initial naive ideas to an increasingly expert understanding of electrical phenomena. A sequence of self-guided experiments uses large capacitors and transient bulb lighting to help students confront their misconceptions, grasp the physics of current propulsion and build intuitive explanatory models.

The core experiments stimulate students to model mobile charge as a compressible fluid and electric potential as "pressure" in the fluid. They learn that a pressure difference is what makes charge move through a resistor. The advanced experiments reveal two kinds of charge and distant action, which suggests modeling fields as pressure raising/lowering "halos" around ± charges. Connections between the electron, the atom and mobile charge in circuits are also explored.

CASTLE instruction gives priority to development of qualitative reasoning skills. No prior knowledge of electricity is required, making the curriculum accessible to students in all levels of high school physics.

The CASTLE approach originated in the research of Professor Melvin S. Steinberg of Smith College. The complete curriculum was developed by a team of college and high school physics teachers under a National Science Foundation grant. Extensive testing has shown superior conceptual and confidence gains. In 1994, CASTLE was certified a proven effective program by the U.S. Department of Education's Program Effectiveness Panel.

In addition, the AAPT PTRA group has adopted CASTLE as has the C3P group and the Modeling Group demonstrating that CASTLE is being chosen by the leaders of physics education as the preferred method for teaching electricity.

The Standard CASTLE Kit contains all the materials needed (except for three D batteries) for two students to work through a complete introduction to basic electricity.  The Economy CASTLE Kit contains all the materials needed (except batteries) for eight students. 

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  • 25,000 µF Capacitor -- Provides the foundation for this intuitive introduction to current electricity.
  • Wires with Alligator Clips -- Ten color-differentiated wires make circuit connections quick and easy -- no soldering or wire twisting.
  • Battery Holder -- Securely holds batteries and yet makes them very visible so that their function within the circuit is evident.
  • Miniature Light Bulbs -- Differently shaped bulbs have different resistance values.
  • Curriculum Guide Download (pdf) -- Contains a teacher's manual (pdf) with comprehensive background information and a student manual (pdf) for printing and distributing in class. Sections may be printed individually as needed.


The Standard CASTLE Kit includes all the materials needed (except for three D-cell batteries) for two students to work through a complete introduction to basic electricity.

Also includes a Material Safety Data Sheet (MSDS).

  • 25,000 µF capacitor (20 volts, nonpolar)
  • #14 light bulbs (4)
  • #48 light bulbs (6)
  • 10 Ohm Resistors (4)
  • Miniature light bulb sockets and stands (4)
  • Wires with alligator clips (10)
  • Battery holder (spring-loaded)
  • High quality compass
  • Storage box

Step 1: A capacitor is charged by a battery. By observing the bulbs and nearby compass, students can monitor the current as it flows and then slowly subsides. Note that the bulbs glow dimly with two bulbs in series.

Step 2: The battery is removed and current flows in the opposite direction (note the compass deflection) as the capacitor recharges. Students learn that charge acts like a fluid in the capacitor plates that can be compressed and depleted.

Step 3: A single bulb is lit by the same charged capacitor. The lamp glows brighter but for a shorter time. Students learn the importance of rate of flow in understanding current.

Typical Experiments

Core Curriculum

  • What is happening in the wires?
  • Where does the moving charge originate?
  • What do the light bulbs do?
  • What makes the charge move?
  • How is the "pressure" in a wire determined?
  • How are values of circuit variables measured?



Advanced Curriculum

  • How do motors and generators work?
  • Do insulators contain charge? What are electrons?
  • What causes "pressure" in distant conductors?
  • How do transistors work? What is AC?


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