When the circuit is completed, electricity flows and the needle moves. Electricians carry meters on the job so they can make sure all the electricity is off before working on a wire. Things must be unplugged before being fixed to prevent burns or electrocution. Technology extends our abilities to observe and measure. Designing a tool to perform specified tasks requires trial and error.
Any invention is likely to lead to other inventions.
Once an invention exists, people are likely to think up ways of using it that were never imagined at first. And now . . . Then encourage them to explore the materials and possibilities. Explain their observations and share the results of their initial investigations.