According to Ohm's law, $$\text{potential difference} = \text{resistance}\times\text{current}$$ Also, current remains the same everywhere.

Now when current passes through a bulb, the electric potential decreases because $$\text{electric potential} = \frac{\text{joules}}{\text{coloumb}}$$ and some of the electric energy is converted into light energy by the bulb. So after passing through a bulb, the number of joules of electric energy a single charge carries will get lower, i.e electric potential decreases which means the potential difference decreases. So by Ohm's law, the current should decrease too. This contradicts the fact that current remains same everywhere.

So how can current remain same when potential difference decreases?


It looks like you are confusing electric potential with electric potential difference. The electric potential difference is a measure of how much the electric potential will decrease (or increase). If the electric potential decreases across a bulb that doesn't mean the potential difference decreases it means that there is a potential difference.

Imagine you have a hill. At the top of the hill the gravitation potential is 200 J/kg. At the bottom of the hill the hill the gravitational potential is 50 J/kg. We would say going down the hill there is a gravitational potential difference of -150 J/kg. No matter how many kg of stuff go down that hill the potential difference is not going to change. It's still -150 J/kg.


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