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Resistors limit current.
Later in this Chapter, you will find out how to calculate a suitable value for this resistor. The 'box' symbol for a fixed resistor is popular in the UK and Europe. Transducers are electronic components which convert energy from one form into another, where one of the forms of energy is electrical. A light dependent resistor , or LDR , is an example of an input transducer . Changes in the brightness of the light shining onto the surface of the LDR result in changes in its resistance.