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Question

Can we use ac ammeter to measure dc current ?

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Solution

Dear Student , By AC ammeters if you mean Moving Iron type or Electrodynamo meter type then these ammeters can be used to measure both AC and DC, as the deflecting torque is either proportional to the square of the current or product of the currents respectivelyDC ammeters consist of a permanent magnet and a moving coil through which the test current flows. The moving coil is held in place by a spring. The torque on the coil is proportional to the current flowing through it, so its deflection is proportional to the current. The display scale is linear. These instruments are simpler to make compared to the AC ammeters. If we pass AC through a DC ammeter then the coil torque will reverse its direction 50 times a second and it will vibrate at 50 Hz. Due to the large inertia of the moving system, it will appear as stationary. AC ammeters are are of 3 types. Moving iron. Here the moving piece is unmagnetized soft iron. It gets magnetized by the current in the fixed coil and produces a torque proportional to square of the current. Due to squaring property, the direction of the torque is same, irrespective of current. Thus it can be used for AC and DC both. Electrodynamometer. Here, the fixed coil and moving coil are connected in series. Here also it produces a torque proportional to square of the current and due to squaring property, the direction of the torque is same, irrespective of current. Thus it can be used for AC and DC both. Anemometer. It uses the heating effect of current. It can be used for AC and DC both. Regards


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