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Question

I found the mention of 'oscillograph' in a numerical under the electrostatics chapter. Pls could you explain to me what this oscillograph actually is??

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Solution

The Oscillograph is an instrument for indicating and recording time-varying electrical quantities, such as current and voltage. The two basic forms of the instrument in common use are the electromagnetic oscillograph and the cathode-ray-Oscillograph, the latter is also known as a cathode-ray-oscilloscope, which, strictly speaking, is purely an indicating instrument, while the oscillograph can make permanent records.

The former type is the one you have to study. It is basically a galvanometer(coil connected to a needle with permenent magnet inside) with a pen attached to its end. the pen moves when there is changein the the current flow due to electromagnetic interaction. The pen traces an ink record on a moving paper chart. The most common device of this nature is the electrocardiograph, which employs a coil of fine wire with many turns and is used for studying heart action.

The light-beam oscillograph has much less weight to move than does the pen-writing instrument and so responds satisfactorily to higher frequencies, about 500 Hz, or cycles per second, compared with 100 Hz for the pen assembly. It uses a coil to which a small mirror is attached. A beam of light is reflected from the mirror onto a photographic film moving at a constant speed. The cathode-ray oscillograph makes use of a sharply focused electron beam to display the relationship between variable quantities on a luminescent screen similar to that used in a television. It may be either a three- or a four-dimensional recording device, the latter being very versatile. Recording is by transfer of energy to a light-sensitive record, using either an optical-lens system or a fibre-optic faceplate. It can be employed at frequencies in the megahertz range.


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