Practical electro-therapeutics and X-ray therapy : with chapters on phototherapy, X-ray in eye surgery, X-ray in dentistry, and medico-legal aspect of the X-ray / by J.M. Martin.

  • Martin, James Madison, 1866-1947.
Date:
1912
Catalogue details

Licence: Public Domain Mark

Credit: Practical electro-therapeutics and X-ray therapy : with chapters on phototherapy, X-ray in eye surgery, X-ray in dentistry, and medico-legal aspect of the X-ray / by J.M. Martin. Source: Wellcome Collection.

Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.

    25/456 (page 21)
    Simplifying Ohm's law, the following formulas will be easily remembered: EMF EMF (1) C = -ir (2) R=—£- (3) EMF = RxC. In order to fix the above rules in the student's mind, the follow- ing practical problems will be of service: Example.—During the therapeutic application of the direct current the voltage is 110, and according to the reading of the milliamperemeter the current strength is 10 milliamperes (%0o A). What is the resistance in ohms offered by the patient ? Applying the formula that the resistance is equal to the electro- motive force divided by the current strength, we have the follow- ing statement according to formula No. 2. EMF 110 V 110 V —q— = iq yr = jy x = 11,000 ohms, the resistance offered by the tissue /10° of the patient. Example.—During the therapeutic application of the direct cur- rent the voltage is 110, and according to the milliamperemeter the current strength is 20 milliamperes (%0 A). What is the resist- ance offered by the patient's tissues? EMF 110 V 110 V ■ q = 9Q ]vra = J/—T == 5)500 ohms, the resistance offered by the tissue '50 of the patient. Many other problems could be given to illustrate the application of the above rules, but we believe that every man who is qualified to take up this work will grasp the meaning of Ohm's law, and will be able to make a practical application when necessary.