The operation of all induction instruments depends on the production of torque due to:

• A. The reaction between a flux φ1 and the eddy currents induced in a metal disc or drum by another flux φ2 .φ2 is depends on the current or voltage to be measured φ1 is constant
• B. The main flux produced by the quantity to be measured
• C. The reaction between a flux φ­1 and the eddy currents induced in a metal disc or drum by another flux φ­2 .φ­1and φ­2 are dependent on the current or voltage to measured.
• D. The reaction between a flux φ­1 and the eddy currents induced in a metal disc or drum by another φ2.Φ1 is depends on the current or voltage to be measured, φ2 is constant