The potential difference at the terminals of the open current source is 4 V.

The potential difference at the terminals of the open current source is 4 V. Determine the internal resistance of the current source if the current strength is 0.8 A.

Initial data: φ1 – φ2 (potential difference at the terminals of an open source) = 4 V; R (resistance of the outer section of the circuit) = 4 ohms; I (current in the current source) = 0.8 A.

The internal resistance of the current source is determined from the formula: φ1 – φ2 = I * (R + r), whence r = φ1 – φ2 / I – R.

Let’s calculate: r = 4 / 0.8 – 4 = 5 – 4 = 1 Ohm.

Answer: According to the calculation, the internal resistance of the current source is 1 ohm.