SubSection | Atomic Physics and Radiation | PHYSICS A. Helmholtz Coils
Connected to a suitable d.c. supply, the coils provide a substantially uniform field in the central space. Each coil has a moulded plastic former 152mm diameter with 320 turns of 22 s.w.g. enamelled wire giving a mean diameter of 136mm. The former is mounted on a boss provided with 2, 4mm sockets and is fitted with a support rod. The rod has a sliding boss which locks into the tapered hole in the base of the Universal Stand.
Dimensions of coil and support rod 305 x 152 x 25mm. Use with the Universal Stand.
Supplied complete with instructions. Direct Delivery – up to 2 weeks E8A49475
B. Planar Diode
The diode is used to show the basic thermionic effects in vacuum tubes, including:
Current flow between an incandescent filament and a cold electrode (the Edison effect). Determination of e/m by the displacement method using Helmholtz coils.
Characteristic anode current/anode voltage curves for different filament temperatures.
Application of a diode as a rectifier.
The diode consists of a basic glass spherical body with a cylindrical neck, containing a tungsten filament with 4mm connections sockets in the plastic cap on the neck and a circular anode plate connected to a 4mm plug connection on the sphere. Use with the Universal Stand.
• Optimum anode voltage: max 500V • Maximum anode current: 2.5mA at 300V • Maximum filament voltage: 7.5V Supplied complete with instructions. Direct Delivery – up to 12 weeks E8A49505
C. Perrin Tube
The Perrin tube may be used to show that charge can be accumulated in the Faraday pail incorporated, that the charge does not disappear when the filament is switched off and therefore that the cathode rays must consist of charged particles. Electron deflection sensitivity may be measured using Helmholtz coils to deflect the beam.
Cathode ray tube operation may also be demonstrated, using a ‘secondary coil’ for the transverse field. The tube comprises a standard spherical glass body with a cylindrical neck containing a diode electron gun with filament and cylindrical anode, and a Faraday’s pail in the sphere, at 45° to the axis. Connections to the diode electron gun are via 4mm sockets in the moulded cap and the Faraday’s pail connection is via a 4mm plug in 1 of the side caps. The end of the sphere has an internal phosphor coating providing a luminescent screen. Use with the Universal Stand.
• Maximum filament voltage: 7.5V. • Anode voltage: 2000 to 5000V.
• Typical operation at 4000V: anode current 1.8mA beam current 4µA.