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Complete E/M Apparatus for the Electron

Have your students measure the ratio of charge to mass for an electron.

Supplier:  Science First EP20

Catalog No. S63317ND

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Requires : Requires 115VAC 50/60Hz.



This classic experiment consists of a vacuum tube mounted inside a pair of Helmholtz Coils that provides a transverse magnetic field. An electron gun, placed inside the tube, points downward and generates a beam of electrons at an energy controlled by adjusting the Accelerating Voltage knob on the apparatus. The magnetic field inside the tube is controlled by adjusting the Coil Current knob on the unit. Electrons are bent into a circle in accordance with the Lorentz Force Law qvxB. This beam is made visible by placing a small quantity of Helium gas at low pressure in the vacuum tube, which glows when struck by the electrons.
The ratio of charge over mass for an electron can be calculated knowing the diameter of the circular path, the current applied to the Helmholtz coil, 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 highly reproducible results. Comes completely assembled with the electron tube, Helmholtz coil, and integral current and voltage power supply.

Order Info

Overall dimensions: 19 x 12 x 14-3/4 in.



Complete E/M Apparatus
115 VAC 50/60 Hz
38 cm
11.8 x 15.7 x 15 in. (30 x 40 x 38 cm)
15.7 in.
15 in.
For the electron
11.8 in.
30 cm
40 cm
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