What is rheostat function?
A variable resistor used to regulate current is called a rheostat. It is a wire that has been wounded and its resistance varies.
It comprises a bare manganin wire stretched over an insulating cylinder. The ends of the wire are connected to fixed terminals A and B, while a sliding contact attached to a third terminal C allows for the adjustment of resistance by moving along the wire. Rheostat act as a variable resistor and as a potential divider.
Brief History
Sir Charles Wheatstone invented the rheostat in the nineteenth century. He used a long tube with coiled wires wrapped around it and an adjustable slider.Rheostat Symbol
 |
| Rheostat symbol diagram |
The symbol for a
rheostat is typically represented as a zigzag line, often with an arrow
indicating the direction of increasing resistance. This symbol is commonly used
in circuit diagrams to denote the presence of a variable resistor or rheostat.
Working of Rheostat
An electric circuit's three primary parameters are the circuit's resistance, the current flowing through it, and the voltage applied to it.We now understand the interdependence of these parameters. In other words, we can adjust the circuit resistance or the applied voltage to alter the current.
Basically, all we're doing when we can use a rheostat in a circuit is adjusting the circuit resistance in order to adjust the current. Since the resistance and current have an inverse relationship, we will increase the rheostat's resistance if a decrease in current is necessary. Similarly, we would only lower the rheostat's resistance if we needed to increase the current.
It's also essential to remember that each rheostat has a resistance rating. The minimum resistance and maximum resistance of a rheostat with a 500 kΩ rating are 0 and 500 kΩ, respectively.
It is possible to adjust the resistance of any given rheostat. Three factors are known to influence resistance: Length, Type, and cross-section Area.
The resistance of the rheostat can only be changed by adjusting the effective length with the help of a sliding contact. The length between the fixed terminal and the sliding terminal's position is known as the effective length. The resistance of the rheostat varies with the effective length.
Types of Rheostat
Linear Rheostat
These are the rheostat varieties with a linear resistive lane that allows for smooth movement of the sliding terminal over the lane. One of the two permanent terminals has a connection to the slider. Because of the cylindrical aspect of its resistive element, the linear rheostat is often referred to as a cylindrical rheostat. These rheostats are used in educational and scientific settings in laboratories.Rotary Rheostat
These are the varieties of rheostats that have a resistive lane that rotates. These rheostats are commonly known as circular rheostats since the resistive element used in them has a circular shape. The wiper or slider travels in a straight line. The shafts hold the wiper in place. Power applications frequently use these rheostats.Preset Rheostat
They are referred to as trimmers or preset rheostats, and these are the rheostat types that are utilized in printed circuit boards. These are tiny and frequently seen in calibrating circuits.Rheostat as a Variable Resistor :
A rheostat can be used as variable resistor. It can be utilized as a variable resistor by inserting the sliding terminal C and one of the fixed terminals, let's say A, into the circuit as shown in figure. The resistance between terminal A and the sliding contact C is adjusted. Shifting the sliding contact away from terminal A increases the wire's length, thereby increasing resistance. If the sliding contact is moved towards A then length of wire decreases and as a result result resistance also decreases.
Rheostat as a Potential Divider:
A potential difference applied between points A and B with the help of a battery. If R is the resistance of the wire of length AB and I is the current flowing through it then according to ohm law:
V = IR
I = V/R .....(1)
To use it as potential divider the output is taken between the points B and C which gives the difference of potential between these two points as show in the figure. If r is the resistance of the wire due to the sliding contact C at any point then the difference of potential between B and C will be
VBC = I x r
Putting value of current in above equation
VBC = (V/R) x r .....(2)
This circuit can be provide potential difference varing from 0 to the full potential difference of the battery. If the sliding contact C is moved towards B then the length of wounded wire decreases and hence the resistance(r) of the wire decreases, so according to the equation(2) the potential difference between two points B and C also decreases.
On the other hand if the sliding contact is moved towards the end A and away from B the length of wounded wire increases and resistance r of the wire increases, so according to the equation(2) the potential difference between the two points B and C also increases.
Use of Rheostat :
Rheostats have several practical applications due to their
ability to regulate electric current. Some common uses include:
1. Dimmer Switches: In lighting systems, rheostats control the brightness of lamps and bulbs by adjusting the flow of current.
2. Motor Speed Control: Rheostats are used to regulate
the speed of electric motors in various devices such as fans, drills, and small
machinery.
3. Heating Control: They control the amount of heat
generated in devices like electric heaters, ovens, and stoves by adjusting the
resistance in the heating elements.
4. Laboratory Equipment: Rheostats are integral
components in laboratory setups for conducting experiments that require precise
control over electrical parameters.
5. Process Control: In industrial applications,
rheostats regulate variables like temperature, pressure, and flow by adjusting
the current passing through heating or cooling elements.
6. Educational Demonstrations: Rheostats are often used
in educational settings to demonstrate the principles of electric circuits and
resistance.
Difference between Rheostat and Potentiometer
| Rheostat | Potentiometer |
|---|---|
| It's a device that uses resistance adjustments to control current. |
It is a device that uses voltage changes to measure electromotive force. |
It doesn't always make use of all three of its terminals. |
It employs all three of its terminals. |
| It is not suitable for use as a potentiometer. |
It's always functional as a rheostat. |
It is employed in the control of lights, motors, etc. Given its ability to manage increased voltage and current. |
It is also used in electronic regulators and reference setters. |
Rheostatic Braking :
Rheostatic braking is a method of slowing down electric motors that entails converting the motor's kinetic energy into heat energy and dispersing it through resistors. This method is widely applied in both electric trains and industrial machinery.FAQs:
What is rheostat in physics ?
A rheostat is a type of variable resistor that is used to adjust the resistance in order to control the amount of electric current flowing.
What distinguishes resistance from a rheostat?
Rheostats and resistances vary in that rheostats are electrical resistors with two terminals, whereas resistances are parameters that may be continually adjusted by turning a knob.
Why is a rheostat used?
An electric circuit's resistance can be adjusted with the use of a rheostat. By adjusting the resistance, a rheostat, a variable resistor, enables manual control over the flow of electric current. Electric current flow can be managed in a circuit by utilizing a rheostat.
Which principle does the rheostat use?
