Light-Dependant Resistors

Question 1

When does LDR have a high resistance?

Answer 1

• Dark conditions.

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Question 2

When does LDR’s have low resistance?

Answer 2

• In the light.

Question 3

What does the light intensity to resistance graph look like?

Answer 3

• Low Light intesinty= High resistance.

- High Light Intesintity= Low resistance.

Question 4

How do mobile phones turn the screen of when in conversation?

Answer 4

• In light:
• Resistance of the LDR= Very low.
• So: Takes very little energy for the current to pass through the circuit.
• P.d across the LDR is low.
• Because p.d is shared between components in series:
• the p.d across the lamp is large.
• lightlights the screen.

Question 5

What happens when the phone is held upon someones ear?

Answer 5

• LDR is in darkness.
• Resistance of the LDR increases sharply.
• Takes a great deal of energy for the current to pass through the LDR.
  So: P.d across the LDR is high.
• Less eletrical energy is avaibale for the lamo.
• P.d cross lamp is low so lamp is dim.