Introduction
In this lab, students investigate how efficiently an electric heating device converts electrical energy into useful thermal energy by heating water. While electrical devices may appear to convert energy directly into a desired outcome, some energy is always lost to the surroundings as heat, sound, or light. In this investigation, efficiency is estimated by comparing the electrical energy supplied to the device with the thermal energy gained by the water. Any energy used to heat the container or lost to the surroundings is considered inefficiency in the system. By measuring both the electrical energy input and the thermal energy gained by water, students calculate efficiency and analyze why no device is 100% efficient.
Student Objectives
Students will be able to
- Measure electrical energy input using power and time.
- Calculate thermal energy gained by water using mass, temperature change, and specific heat.
- Calculate the efficiency of an electric heating device.
- Explain why energy efficiency is always less than 100%.
- Connect appliance efficiency to energy conservation and environmental impact.
Materials
Per Group
- Student Handout
- Calculator
- Electric kettle or hot plate and beaker
- Water
- Thermometer
- Digital scale
- Stopwatch or timer
- Measuring cup
- Kill-a-Watt or similar power meter
Safety Precautions
- Review safe handling of electrical devices.
- Warn students about hot surfaces and hot water.
- Ensure cords are kept away from water spills.
- Supervise all heating steps closely.
Procedure
- Divide students into groups of 2 or 3 and provide each group with the Student Handout.
- Review safety procedures with the class, emphasizing hot surfaces and electrical safety.
- Instruct students to carefully read and follow the instructions on the Student Handout to conduct the investigation.
- Instruct groups to carefully collect and record their data.
- After data collection, each group will share their results with the class.
- Compile class data on the board or shared document so students can compare efficiencies across multiple trials.
- Instruct each group to complete the analysis and conclusion sections of the Student Handout.