# How long should a current of 2.5A (amperes) flow through a conductor

**How long should a current of 2.5A (amperes) flow through a conductor with a resistance of 18 ohms and so that 81kJ of energy would be released in it?**

We translate the values from given to the SI system:

Q = 81 kJ = 81000 J.

The energy released in the conductor when an electric current passes through it:

Q = P * τ

Formula for determining electrical power:

P = U * I

According to Ohm’s law, the amount of current is directly proportional to the applied voltage and inversely proportional to its resistance:

I = U / R

U = I * R

Substitute into the expression for the power:

P = U * I = I * R * I = I² * R

Substitute in the expression for the energy:

Q = P * τ = I² * R * τ =

Let us express time from this expression:

τ = Q / (I² * R)

Substitute the numerical values and find the time:

τ = Q / (I² * R) = 81000 / (2.5² * 18) = 720 s.

Answer: 720 sec or 12 min is needed.