P2 - Light-Dependent Resistors

What does LDR stand for?

Light Dependent Resistor

What is the symbol for an LDR?

A resistor symbol with a circle around it and two arrows pointing towards it

What happens to the resistance of an LDR in darkness?

The resistance increases

What happens to the resistance of an LDR in bright light?

The resistance decreases

How does light intensity affect an LDR?

As light intensity increases, the resistance of the LDR decreases

Why is the LDR useful in circuits?

Because its resistance changes with light level, so it can detect light

Is an LDR an ohmic conductor?

No, because its resistance is not constant

What does an ohmic conductor show on a current-voltage graph?

A straight line through the origin (current is directly proportional to voltage)

How is potential difference shared in a series circuit?

The total potential difference is shared between components

What happens to potential difference across an LDR in bright light?

It is low because resistance is low

What happens to potential difference across an LDR in darkness?

It is high because resistance is high

What is the effect of low LDR resistance on the other components in series?

They get a larger share of the potential difference

What is the effect of high LDR resistance on the other components in series?

They get a smaller share of the potential difference

How can an LDR be used in a mobile phone screen?

To turn off the screen when the phone is held to the ear (darkness increases resistance, reducing current to the lamp)

Why does the phone screen go dim when held to the ear?

The LDR is in darkness, so resistance increases and less potential difference is left for the screen lamp

How is an LDR used in garden lamps?

The lamp turns on when it is dark (LDR resistance increases and triggers the light circuit)

What is the relationship between light intensity and resistance in an LDR?

Inversely proportional (more light = less resistance)

Give an example of a device that uses an LDR

Mobile phone, garden light, automatic night light

In an LDR circuit, what happens if light level drops suddenly?

Resistance increases, causing the circuit to change its behaviour

Why is it important to understand LDRs in electronics?

They are used to sense environmental light levels and automatically control circuits

What is a practical example of an LDR application in real life?

Automatic street lights, phone screens, light-sensitive alarms