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Text c rheostats

One of the technical terms for a rheostat is a variable resistor. This term is appropriate because it indicates how the rheostat works. Rheostats are also referred to as potentiometers.

A piece of resistance wire, usually in coil form, is connected at one end to a battery feed. The other end of the resistance wire isn’t attached to anything. The wire going from the rheostat to the load is attached to a movable element called a wiper. The wiper is arranged so it rubs against the length of the resistance wire. When the wiper is close to the battery-feed end of the resistance wire, the rheostat adds little extra resistance to the circuit. As you slide the wiper to the far end of the resistance wire, current flows through increasingly more resistance to get to the wiper, reducing current flow to the load.

Within the design range of the rheostat, you can dial in no resistance up to high resistance, or any amount in between. This gives you precise control over the amount of current being fed to the load. The most common use for a rheostat in a car is the dimmer for the instrument-panel illumination lamps. In most OEM headlamp switches, the dimmer rheostats is operated by twisting the headlamp knob.

Rheostats designed for automotive applications are usually not capable of carrying high current without burning out. Circuits with high currents in need of variable resistance are usually controlled by a single-pole, multiple-throw slide switch. The selector for a three-speed heater-blower motor fits this category. The selector switch regulates motor speed by selecting various

Черкаський політехнічний технікум

Тексти та завдання для ІІІ курсу спеціальності ЕА

Підготувала викладач Кудрява О.В.

resistors in series with the motor. In the ‘LOW’ position, the full set of resistors is selected. Each

higher speed bypasses one more resistor, until, in the ‘HIGH’ position, all resistors are bypassed, providing full current to the motor. The resistors are capable of carrying high current without bunting out. They do get hot, though, so they're usually located in the blower air-stream.

Exercises Unit 6 (text c)

1. Put the phrases in right order to make up a dialogue.

1. I’d like to find out more information about the length of wire and the place of its location.

2. A slider moving across the windings of the rheostat changes the value of the resistance between its terminals.

3. What is called a rheostat?

4. I am very grateful for such useful information.

5. Yes, of course. A rheostat is a wire wand device, wires for rheostat are produced of materials having high resistivity.

6. What is a rheostat used for?

7. A device used in the circuit in order to regulate its current is called a rheostat.

8. It is a very interesting question as it’s impossible to answer exactly. Commonly a comparatively short length of wire is used: it is wound on a ceramic or on some other insulator.

a) ____ b) _____ c) ______ d) ______

e) ______ f) ______ g) ______ h) ______