Answer:
Resistance
Step-by-step explanation:
In a circuit, voltage source (cell or battery), key (for closing and opening circuit), resistance and a conducting wire are main components. Ohm's law states that current flowing in the circuit is proportional to the potential difference across the two ends.
V = I R
Where R is the resistance. Current also depends on the resistance. Greater resistance means lesser current would flow.
A light bulb and toaster represent resistance. These devices are based on Joule's Heating. When current passes through a resistance, it heats up and energy is lost as heat in case of toaster and as heat and light in case of light bulbs.