Question

A common misconception is that current is used up and steadily declines as it progresses through a series of resistors. That would be violation of conservation of charge. What is in fact used up is electric potential energy of the charge carriers, some of that is delivered to each resistor.

Explain why current in a real circuit gradually decreases with time compared to its initial value.

a)As current flows in circuit, electrons leave the negative terminal and other electrons reach the positive terminal. The potential difference across circuit gradually declines, and so current decreases.

b)As current flows in circuit, the internal resistance of the battery increases over time. This raises the equivalent resistance of the circuit, and current gradually decreases. 

c)As current flows in circuit, the resistance of the resistors outside the battery gradually increases. This raises the equivalent resistance of the circuit, and current gradually decreases.