Lab 4 explained different sources of electricity and how they are affected by different variables. For example, a thermocouple produces more electricity when more heat is applied and a solar cell produces more electricity when it has a larger source of light. When talking about batteries, the polarity of the batteries is essential to calculating the applied voltage. If they are connected in series aiding the voltage will be additive. If they are connected in series opposing, the voltage will be zero as the polarity restricts any electrical movement. When connected in parallel, the current will increase but the voltage will remain the same as voltage is the same everywhere in a parallel circuit.