An instrument used for measuring the intensity of light

1. Analyze the question The question asks which instrument measures the intensity of light. Each option is a measuring device, so we need to match each one to what it measures.

2. Explain the concept Look at the word roots:

• Photo- means "light"
• Thermo- means "heat"
• Anemo- means "wind"
• Hygro- means "moisture" or "humidity"

3. Step-by-step solution

• A. Thermometer measures temperature, not light.
• B. Photometer measures light intensity (brightness). This matches the question.
• C. Anemometer measures wind speed.
• D. Hygrometer measures humidity, the amount of water vapour in the air.

4. Answer The correct option is B. photometer.

5. Tip Use the prefixes to match instruments to what they measure:

• Photo = light → photometer
• Thermo = heat → thermometer
• Anemo = wind → anemometer
• Hygro = humidity → hygrometer

Other ecological instruments that often appear in JAMB are the barometer (atmospheric pressure), rain gauge (rainfall), and secchi disc (water turbidity). Learning these prefixes can earn you easy marks.