A cell or a battery is a source of electrical energy. $\rightarrow$ The chemical reactions within a cell or battery generate potential difference between its two terminals. $\rightarrow$ This p.d. gets the electrons in motion, to flow through any circuit, i.e., through a resistor or a system of resistors connected to the cell or battery. $\rightarrow$ So to maintain this flow, the source has to keep expending its energy. $\rightarrow$ But only a part of the source energy in maintaining the current may be consumed into useful work. $\rightarrow$ The rest of the source energy is converted into heat to raise the temperature of the electrical gadgets.
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