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e/m Apparatus
Item #P6-3100
$3,459.00
Bundle Discount
| Unit Price | $3,459.00 |
| 3+ | $3,286.00 |
Measure the electron charge-to-mass ratio
Use the e/m Apparatus to demonstrate the Lorentz Force Law and measure the charge-to-mass ratio of the electron. Students reproduce J.J. Thomson’s experiment and watch a glowing beam curve in a uniform Helmholtz-coil field. Adjustable accelerating voltage and coil current change beam radius in real time.
By measuring orbit size, learners connect electric and magnetic forces to circular motion and calculate e/m quickly. Clear scales, built-in power supply, and safe controls make results fast and repeatable.
Why Teachers Love e/m Apparatus
- Affordable way to teach a core constant: delivers a true e/m measurement lab without the cost or complexity of piecemeal components.
- Self-contained and easy to run: integrated Helmholtz coils, tube, meters, and matched power supply mean fewer parts to gather and a faster setup.
- Huge visual payoff: the fluorescent electron beam makes field effects obvious and engaging.
- Quantitative, not just “wow”: students calculate e/m with repeatable, publishable-quality data
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Product Details
What You Can Teach with the e/m Apparatus
- Lorentz Force & Charged-Particle Deflection: Watch the electron beam bend in electric and magnetic fields and relate direction to qv × B.
- Circular Motion in a Magnetic Field: Measure orbit diameter to connect centripetal force, radius, and field strength.
- Helmholtz Coils & Uniform Fields: Investigate how coil spacing and current create a near-uniform magnetic field.
- Electron Charge-to-Mass Ratio (e/m): Use accelerating voltage and beam radius to calculate a fundamental constant.
- Energy of Accelerated Charges: Link electron speed to electric potential energy and conservation of energy.
How it Works
The e/m Apparatus (with power supply) consists of a vacuum tube mounted inside a pair of Helmholtz Coils that provide a transverse magnetic field. An electron gun placed inside the tube points downward and generates a beam of electrons controlled by adjusting the Accelerating Voltage knob. The magnetic field inside the tube is controlled by adjusting the Coil Current knob. Electrons are bent into a circle in accordance with the Lorentz Force Law qv x B. This beam is made visible by placing a small quantity of helium gas at low pressure in the vacuum tube; the helium glows when struck by the electrons.
The ratio of charge over mass for an electron can be calculated using the diameter of the circular path, the current applied to the Helmholtz coils, and the voltage used to accelerate the electrons. The accelerating voltage can be varied from 100 to 500 VDC and the current varied from 0-3A DC to provide a wide variety of beam energies and deflection fields. The orbit diameter itself is measured on an internal glass scale that includes fluorescent marks for easy measurement. The mark glows when the beam strikes it, making it easy to determine the exact beam diameter. Accelerating voltage and deflection current values are displayed on three-digit panel meters that allow quick and precise measurements. The voltage and current power supplies are controlled by an onboard microprocessor to ensure stable, precise, and easily reproduced results. Comes completely assembled with the electron tube, Helmholtz coils, an integral current and voltage power supply and complete usage manual.
Products being sold are not toys. They are for Educational / Laboratory use only. They are not for use by children 12 and under.
Warning: California Residents
WARNING: Cancer & Reproductive Harm — www.P65Warnings.ca.gov
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