Light-dependent resistors

Question 1

What does LDR stand for?

Answer 1

Light-dependent resistor

Question 2

What is a light-dependent resistor (LDR)?

Answer 2

• is an electronic device that senses the amount of light falling on its surface
• it is an input device
• *see figure 11.14 and 11.15 in your book

Question 3

How is an LDR inserted into a circuit?

Answer 3

It can be inserted any way around into a circuit - because it is a non-polar device

Question 4

How does an LDR work?

Answer 4

• the electrical resistance of an LDR in a circuit decreases as the light falling on it gets brighter (or increases).
• This allows the current flowing through the circuit to increase.
• in the same way, if the light gets duller (decreases), the resistance in the circuit increases and the current flowing through the circuit decreases

Question 5

In which two ways are the LDR circuit used?

Answer 5

• 1) to amplify the LDR signal to an output device (i.e. loudspeaker)
• 2) to switch an output device on or off (i.e. lamp, buzzer or motor)