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e/m Apparatus (Helical Method)

This experiment measures e/m, the charge to mass ratio of the electron. In the present experiment a beam of electrons is accelerated through a known potential, so the velocity of the electrons is known. A solenoid  produces a uniform and measurable magnetic field at right angles to the electron beam. This magnetic field deflects the electron beam in a circular path. By measuring the accelerating potential, the current to the solenoid, , and the radius of the circular path of the electron beam, the ratio e/m is calculated.

The e/m apparatus by helical method consists of four major parts :

  1. Standard Solenoid of multi-turned layers fitted on wooden base.
  2. Power supply for Solenoid :
    • I.C Regulated variable Power supply : 0 to 30 V @10 Amp.
    • With Digital Voltmeter and Ammeter.
  3. Cathode Ray Tube Power supply :
    • High Voltage 0 to 1000 V @100 mA.
    • With Digital Voltmeter.
  4. Cathode Ray Tube mounted to movable inner side of the standard solenoid.
  5. Connecting jack.