. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. Magnetic flux Figure difficult to minimize the interference by altering the plane of the loop. Fortunately it is often possible to alter the direction of the field. Radiated electromagnetic fields—Whenever an alternating electric current flows round a circuit, systems of electric and magnetic fields may be thought of as growing out of, and collapsing back into, the conductors in sympathy with the successive growth and decay of current. These fields represent energy alternatively deriv
. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. Magnetic flux Figure difficult to minimize the interference by altering the plane of the loop. Fortunately it is often possible to alter the direction of the field. Radiated electromagnetic fields—Whenever an alternating electric current flows round a circuit, systems of electric and magnetic fields may be thought of as growing out of, and collapsing back into, the conductors in sympathy with the successive growth and decay of current. These fields represent energy alternatively derived from, and returned to, the electric circuit. How- ever, not all the energy associated with each growth is returned in the subse- quent collapse. A fraction of it is 'radiated' off into space as an electro- magnetic or 'radio' wave. The effect is extremely small at 50 c/s but becomes important as the frequency is raised into the hundreds-of-kilocycles Amp (b) Figure and above. An electromagnetic wave, as the name suggests, contains both electric and magnetic field components and cannot exist unless both are present. It follows that any system of protection against either pure electric field- or pure magnetic field-borne interference will be effective against radiation, and no specific remedy is necessary. Causes of interference The most ubiquitous kind of interference is due to the supply mains, which shows up as the ail-too familiar 50 cycles wavy line on cathode ray tube traces, and as 'hum' on loudspeakers. It may be borne by electric or magnetic fields, often by both. Another variety is 'impulsive' interference, which appears as a sharp spike and is heard as a 'click'. It is usually electric- field-borne and is caused by the sudden appearance of a large when a mains circuit is broken which contains an inductive load. Switches, thermostats, commutator motors, etc., are potential sources of trouble here. The unexpected reception of the is,
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