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IGCSE · Practice questions · Sensors and how they are used

Sense, compare, act.

Six original Cambridge-style questions on sensors and their uses, with mark-scheme style solutions.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Measure, do not decide.

01
Recall
[2 marks]

State what is meant by a sensor and give one reason why sensors are used instead of a person taking readings.

  • An input device that measures a physical quantity / captures data about its environment. ✓
  • Any one: readings are taken continuously/more often; more accurate; can be used in dangerous or remote places; no need for a person to be present. ✓
02
Apply
[3 marks]

Identify the most suitable sensor for each use.

(a) Detecting a burglar stepping on a mat.
(b) Measuring the amount of fuel left in a tank.
(c) Measuring how fast water moves through a pipe.

  • (a) Pressure sensor. ✓
  • (b) Level sensor. ✓
  • (c) Flow sensor. ✓
03
Apply
[3 marks]

An art gallery must keep its paintings in air that is not too warm, not too damp and not too bright. Identify three sensors it should use.

  • Temperature sensor. ✓
  • Humidity sensor. ✓
  • Light sensor. ✓
04
Explain
[4 marks]

A greenhouse uses a moisture sensor to keep the soil watered. Explain how the sensor and microprocessor keep the soil at the correct moisture level.

  • The moisture sensor measures the water content of the soil and sends the reading (via an ADC) to the microprocessor. ✓
  • The microprocessor compares the reading with a stored value. ✓
  • If the reading is below the stored value, it sends a signal to an actuator to open the water valve / switch on the sprinkler; otherwise it closes it. ✓
  • The process repeats continuously. ✓
05
Explain
[2 marks]

Explain the difference between a moisture sensor and a humidity sensor.

  • A moisture sensor measures the water content of soil (or a material). ✓
  • A humidity sensor measures the amount of water vapour in the air. ✓
06
Analysis
[2 marks]

A student writes: "The temperature sensor switches the heater on when it gets cold." Explain why this is incorrect.

  • The sensor only measures the temperature and sends the reading. ✓
  • The microprocessor compares the reading with the stored value and sends the signal that switches the heater on. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.