What are minimum and maximum positions of rheostat?

Answer: At the time of staring shunt motor field rheostat is minimum and armature rheostat is maximum.

Why rheostat is used in generator experiment?

rheostat, adjustable resistor used in applications that require the adjustment of current or the varying of resistance in an electric circuit. The rheostat can adjust generator characteristics, dim lights, and start or control the speed of motors.

Why the adjustments are done in the field rheostat of generator and motor?

The field rheostat is connected in series with the shunt field circuit. This provides the simplest method of controlling the terminal voltage of a dc generator. … This varies the amount of resistance in the field circuit.

Why is it necessary to cut out all the resistance in the field rheostat while stopping the motor?

Precaution While stopping the motor, all the resistance in the field rheostat is cutout, so that motor speed falls to its normal value; then the line switch is opened. This procedure ensures that, the next time the motor is started, it will be with a strong field and resultant strong starting torque.

What is the purpose of rheostat?

The rheostat is a type of variable resistor that can adjust its resistance so that the amount of power running via a circuit can be modified. It changes the magnitude of the current without interrupting the flow by adjusting the rheostat’s resistance throughout the circuit.

How does a rheostat control the current in a circuit?

The rheostat is a variable resistor used to control the electric current by increasing or decreasing the resistance manually. … Two variables determine the electric current flowing through an electrical circuit. The amount of voltage applied to the circuit and the total resistance of the electrical circuit.

What is cut out position in rheostat?

Rheostat is a variable resistor. It has three terminals. 2 fixed terminals and one variable terminal to vary the resistance. It can be kept in either cut in or cut out position. If kept in cut out position it offers zero resistance.

What does happen when field rheostat gets opened in running condition in DC motor?

As mentioned above if the field circuit is opened, the back emf will drop to zero. With full armature voltage applied this will cause a very large armature current to flow which should normally blow the fuses. … In this case the motor will accelerate and run away until the fuses blow.

Why do we use over compound generators in power stations?

Cumulative compound wound generators are generally used for lighting, power supply purpose and for heavy power services because of their constant voltage property. They are mainly made over compounded. Cumulative compound wound generators are also used for driving a motor.

Why does rheostat have 3 terminals?

Rheostat is a device connected in the circuit to vary the resistance. We can provide the resistance required by just adjusting the wiper. Rheostat is generally having 3 terminals in the circuit. … (i)Rheostat is used when the circuit has to provide high voltage or current.

Why speed control is needed?

In mechanical system, speed varies with number of task so speed control is necessary to do mechanical work in a proper way. It makes motor to operate easily. Shunt motor is a special type of DC motor which runs at a constant speed. But using field and armature rheostat control method we can make it more versatile.

How does a rheostat work?

Connect one wire of your rheostat to either one of the two leads from your voltage source. Connect one lead from the electrical device you want to control to the other lead of your rheostat. Connect the other lead of the device you want to control to the other lead of your voltage source.

Does a rheostat reduce voltage?

A basic rheostat introduces a variable resistance to a circuit. As the resistance increases, voltage drops across the resistor, reducing the voltage applied to other components attached in series with the rheostat.

Why voltmeter is connected in parallel?

A voltmeter is an instrument that measures the difference in electrical potential between two points in an electric circuit. … In order for a voltmeter to measure a device’s voltage, it must be connected in parallel to that device. This is necessary because objects in parallel experience the same potential difference.

Why do potentiometers have three legs?

Notice that the potentiometer has three legs. The outer legs are used for power and ground while the middle is used as an input. This means that the value coming out of the third leg will change depending on how far the knob is turned. Pay attention to which wires are connected to which legs.

How does rheostat affect current?

When we use a rheostat in a circuit, what we are basically doing is changing the resistance of the circuit, to change the current. As the current and resistance are inversely proportional, if a decrease in current is required, we will increase the resistance of the rheostat.

Is rheostat an ohmic device?

To understand and use a rheostat, or variable resistor, in an electrical circuit. … When a material behaves in this way, it is called “ohmic.” Electrical components made from ohmic materials are called resistors.

What is the direction of electric current in an electric circuit?

The direction of an electric current is by convention the direction in which a positive charge would move. Thus, the current in the external circuit is directed away from the positive terminal and toward the negative terminal of the battery.