A heating element with a resistance of 100 ohms released 12 MJ of heat in 20 minutes. What is the current in the circuit?

We start with the formula for the amount of heat: Q (amount of heat) = I (current) ^ 2 (squared) * R (resistance) * t (time). By the condition of the problem, Q we have = 12MJ, where mega is 10 to the 6th power, i.e. Q = 12 * 10 to the 6th power of J (SI system).
Now from the first formula we find what the current strength or I is equal to: I ^ 2 = Q \ Rt, that is, I = square root of Q \ Rt
Now do not forget to convert the time from minutes to seconds (again in the SI system), i.e. t = 20 * 60 = 1200 s. And now we substitute the numbers from the condition into the formula we received and find the current strength: I = square root of (12 * 10 to the 6th power \ (100 * 1200)) = 10 A.
Answer: I = 10 A