Field energy is equal to the co-energy.

Explanation:
In a linear electromagnetic circuit, the field energy and co-energy are related to each other.

- The field energy is the energy stored in the magnetic and electric fields surrounding the circuit.
- The co-energy is the energy stored in the circuit's inductance and capacitance elements.

Field Energy:
The field energy is given by the formula:

E_field = (1/2) * L * I^2

where E_field is the field energy, L is the inductance of the circuit, and I is the current flowing through the circuit.

Co-Energy:
The co-energy is given by the formula:

E_co = (1/2) * C * V^2

where E_co is the co-energy, C is the capacitance of the circuit, and V is the voltage across the circuit.

Comparison:
To compare the field energy and co-energy, let's consider the factors affecting each of them:

1. Inductance and Current:
- The field energy is directly proportional to the inductance of the circuit. Higher inductance will result in higher field energy.
- The field energy is directly proportional to the square of the current flowing through the circuit. Higher current will result in higher field energy.

2. Capacitance and Voltage:
- The co-energy is directly proportional to the capacitance of the circuit. Higher capacitance will result in higher co-energy.
- The co-energy is directly proportional to the square of the voltage across the circuit. Higher voltage will result in higher co-energy.

Conclusion:
From the above comparisons, it can be observed that the field energy and co-energy have similar dependencies on their respective circuit parameters. Both the field energy and co-energy are proportional to the square of an electrical quantity (current for field energy, voltage for co-energy) and the energy-storing elements (inductance for field energy, capacitance for co-energy).

Therefore, it can be concluded that the field energy is equal to the co-energy in a linear electromagnetic circuit.