# What is the resistance of a soldering iron, the current strength of which is 0.3 A, if in 1 hour

August 17, 2021 | education

| **What is the resistance of a soldering iron, the current strength of which is 0.3 A, if in 1 hour it emits an amount of heat equal to 324 kJ?**

I = 0.3 A.

t = 1 h = 3600 s.

Q = 324 kJ = 324000 J.

R -?

The amount of thermal energy Q, which is released when an electric current passes through it, is determined by the Joule-Lenz law: Q = I ^ 2 * R * t, where I is the strength of the electric current, R is the resistance of the conductor, in our case, the soldering iron, t is the time passage of current.

The resistance of the soldering iron R is expressed by the formula: R = Q / I ^ 2 * t.

R = 324000 J / (0.3 A) ^ 2 * 3600 s = 1000 Ohm = 1 kOhm.

Answer: the soldering iron has a resistance R = 1 kOhm.

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