Here’s what we say below the last video in Unit 3, where we go over a similar “loose connection” scenario.
“Note that we didn’t use P = E2/R to calculate the heat, even though we are given voltage supply and resistances. You’ll learn more about this in the next few units, but the reason is when you have loads in a series, each load does not have the full voltage supply. Instead, the “voltage drop” across each load will add up to equal the voltage supply. So, you could only use P = E2/R if you first calculated the voltage drop across each load. Don’t worry if you don’t fully understand that now. We will cover it in more detail in the units to come.”
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