Final answer:
An electrical resistor in a well-insulated tank is used to heat the contents by converting electrical energy into heat energy when current passes through it.
Step-by-step explanation:
The purpose of the electrical resistor in a well-insulated tank is usually to heat the contents of the tank. Electrical resistors convert electrical energy into heat energy when an electric current passes through them. This phenomenon is also used in immersion heaters for heating water. The resistance of the resistor, combined with the voltage applied, dictates the amount of heat generated. This is based on the formula P = V^2/R, where P is the power, V is the voltage, and R is the resistance. Understanding the relationship between these variables is essential when determining the specifications of an immersion heater and its operation, such as calculating the needed resistance and estimating the cost of electrical energy consumed.