Thermistors, Light-Dependent Resistors and Sensing Circuits · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Sensors that split voltage

Science · Energy · ages 15-16
Name ______________________   Date ____________

  1. Light on a light-dependent resistor grows brighter. What happens to its resistance?

    • It stays fixed forever
    • It falls
    • It rises

  2. A thermistor warms up. What happens to its resistance?

    • It falls
    • It rises
    • It freezes

  3. Noor says the bigger resistor in a series pair claims the bigger share of the voltage. Is Noor right?

    Circle one:   True   False

  4. A circuit must turn a lamp on when the room gets dark. Which component does the sensing?

    • A fixed resistor
    • The light-dependent resistor
    • The lamp filament

  5. In a divider, the top resistor is swapped for a much bigger one. What happens to the voltage across it?

    • It rises
    • It vanishes
    • It stays exactly flat

  6. Evening falls and the LDR darkens. What happens inside its divider?

    • Its resistance falls and its share shrinks
    • Its resistance rises and its share grows
    • Nothing changes at all

  7. Kim hangs a heavy load across one divider resistor and the reading shifts. Why?

    • Resistors heal under load
    • Voltage splits alphabetically
    • The load sits in parallel with it and disturbs the split

  8. You must fire a heater when a room gets cold. Which design works?

    • A thermistor in a divider, wired so the midpoint crosses threshold as cooling raises its resistance
    • A fixed pair of resistors with no sensor
    • An LDR wired to ignore light
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Sensors that split voltage W1-mt_d92v1CiqIG-s1

  1. It falls · More light drives an LDR's resistance down.
  2. It falls · Heat drives a thermistor's resistance down.
  3. True · A divider splits supply in proportion to the two resistances.
  4. The light-dependent resistor · The LDR is the part whose resistance answers to light.
  5. It rises · A bigger share of resistance claims a bigger share of voltage.
  6. Its resistance rises and its share grows · Less light means more resistance, which claims more voltage.
  7. The load sits in parallel with it and disturbs the split · The extra branch changes the effective resistance, so the designed split moves.
  8. A thermistor in a divider, wired so the midpoint crosses threshold as cooling raises its resistance · Cooling raises thermistor resistance, and the divider turns that into a firing voltage.
Worksheet · LightMySky