Fig 1 shows standard circuit symbols used in electronic design. A student is designing a light-sensing circuit for an outdoor garden lamp that switches on a...
Question 1 Report
Fig 1 shows standard circuit symbols used in electronic design. A student is designing a light-sensing circuit for an outdoor garden lamp that switches on automatically when darkness falls. The circuit uses several components. One of the symbols shown in Fig 1 represents a component whose resistance changes with light level.
(a) State the name of the electronic component shown in Fig 1. [1]
Answer Details
(a) The component shown in Fig 1 is a Light Dependent Resistor (LDR). [1]
The circuit symbol shows a rectangular resistor body with two arrows pointing toward it. These arrows represent incoming light, which is the standard convention for distinguishing an LDR from a plain resistor or a thermistor. An LDR is a passive component whose resistance decreases when the intensity of light falling on it increases. In darkness, its resistance can be as high as several megaohms; in bright light, it can fall to a few hundred ohms. This property makes it ideal for the automatic garden lamp described: as daylight fades, the LDR's resistance rises, which can be used in a potential divider or transistor switching circuit to trigger the lamp.
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