rheostat Flashcards
what is rheostat
The rheostat can be used to regulate current by altering either the resistance of the circuit or the potential in part of the circuit.
construction
A rheostat consists of a coil of high resistance wire wound on the insulating block with each turn insulated from adjacent turns. Contact is made via a strip from which insulation has been removed. The contact is mounted either on a straight sliding bar or on a pivot turned knob.
variable rheostat or series rheostat
In this device the rheostat is wired in series with the apparatus.
According to ohm’s law, current is inversely proportional to resistance. If all the coil of the rheostat are used, then the resistance is at it maximum and the current is at its lowest. The current increases as the number of turns included are reduced
This arrangement is not suitable for currents applied directly to patients, as it never reduces th current flow to zero.
It usually found in apparatus where an effect on the degree of heating is required, e.g. wax baths.
There is a stabilizing rheostat on ultra-violet lamps
shunt rheostat or potentiometer
The shunt rheostat is wired across the source of potential difference and any other circuit has to be taken off in parallel to it.
This is the type of current regulating mechanism found in apparatus where an electric current has go be applied directly to a patient, as the current intensity can be increased gradually from zero to maximum.
