Questions: Reading a Thermometer

Question 1

You place a thermometer in a cup of warm water. The liquid inside the thermometer rises. Why?

• A. The warm water pushed the liquid up through the tube
• B. The heat from the water caused the liquid in the thermometer to expand and rise
• C. The thermometer is creating its own heat
• D. The liquid is boiling inside the tube

Answer: (B)

When the thermometer is placed in warm water, heat flows from the water into the liquid inside the thermometer. The liquid expands (takes up more space) as it warms, causing it to rise up the narrow tube. This is how thermometers translate temperature into a visible reading you can measure.

Question 2

Water freezes at 0 degrees Fahrenheit.

• T. True
• F. False

Answer: False

False. Water freezes at 0 degrees Celsius, not Fahrenheit. In Fahrenheit, water freezes at 32 degrees. In science, the Celsius scale is standard because it is based on the freezing and boiling points of water: 0 degrees for freezing, 100 degrees for boiling.

Question 3

Why should you read a thermometer with your eyes level with the top of the liquid?

Model answer: Reading at eye level gives an accurate measurement. If you look from above or below, the angle makes the liquid appear to be at a different level than it actually is, which gives you a wrong reading. This error is called parallax.

Parallax is a reading error caused by viewing an instrument from an angle. When your eyes are level with the liquid, you see exactly where it lines up on the scale. From above, it looks lower than it is; from below, it looks higher. Eye-level reading eliminates this error.