Final answer:
To find the percentage uncertainty for a temperature change from 20 °C to 10 °C with an individual reading uncertainty of ±0.5 °C, you calculate the total uncertainty (1.0 °C), divide by the total temperature change (10 °C), and multiply by 100%, which results in a 10% uncertainty.
Step-by-step explanation:
The question revolves around determining the percentage uncertainty when measuring temperature changes with a laboratory thermometer. Since the uncertainty is a constant ±0.5 °C (meaning the reading could be 0.5 °C less or more than the displayed value), the total uncertainty for the change in temperature from 20 °C to 10 °C would be twice the uncertainty of an individual measurement because two separate readings are involved (initial and final). Therefore, the total uncertainty is 0.5 °C + 0.5 °C = 1.0 °C.
To find the percentage uncertainty, we divide the absolute uncertainty by the absolute change in temperature and multiply by 100%. The change in temperature is the final temperature minus the initial temperature, which is 10 °C - 20 °C = -10 °C (we use the absolute value, so it's just 10 °C). Therefore, the percentage uncertainty is (1.0 °C / 10 °C) × 100% = 10%.
The correct answer is D. 10%.