LDR's

Question 1

What is an LDR?

Answer 1

• A resistor that changes resistance depending on the light intensity.

Question 2

What happens to the resistance of an LDR as you increase the light intensity?

Answer 2

• Higher light intensity = lower resistance.

Question 3

Why does your phone screen switch off in dark? Link to LDR’s?

Answer 3

• Dark –> High resistance –> High voltage across LDR (energy transferred)
• Less energy is transferred to the bulb, making it very dim.

Question 4

Explain how street lights switch on in the dark. Mention LDR.

Answer 4

• Light intensity = dull
• Resistance = High
• Potential Difference across LDR increases
• P.D of bulb increases and lights up.

Question 5

If a component has a high resistance, what kind of potential difference would be required?

Answer 5

• High potential difference: more energy to push electrons along (current) , past metal ions in component.

Question 6

Why does the potential difference of a component increase when it has more resistance?

Answer 6

• Because it takes more energy for the current to pass through the component, so potential difference is high.
  More energy transferred

Question 7

Why is a fixed resistor used in street lights?

Answer 7

• Prevent high current
• Which could break components

Question 8

What happens to the overall current of the circuit if the resistance of the LDR increases?

Answer 8

• The overall current will decrease.

Question 9

What is the relationship between light intesnity and resistance?

( 2 points)

Answer 9

• As light intensity increases, resistance decreases.
• Non- linear relationship

Question 10

What is a “potential divider” circuit?

Answer 10

• When P.D is split amongst 2 or more components.

Question 11

Q.)

Explain why the potential difference across the LDR decreases, as the light intensity increase.

Answer 11

• Light intesity up = low resistance
• The fixed resistor has high resistance–> higher PD
• LDR gets lower share –> lower P.D