Point 12 of 12 — Lesson 3: Analog Measuring Instruments – Galvanometer, Ammeter, Voltmeter and OhmmeterQuestion bank: 1 questions (1 with pictures)
12Typical "give reasons" for this chapter
A soft-iron cylinder is fixed inside the coil of the galvanometer: to strengthen the field and make it radial.
The coil is attached to a pair of spiral springs: to supply a restoring torque proportional to the angle and to lead the current to the coil.
A high resistance is connected in series with the galvanometer when it is used as a voltmeter: to limit the current to Ig at FSD and to make the voltmeter draw negligible current.
An ammeter is connected in series and a voltmeter in parallel: so that the ammeter carries the whole current of the branch and the voltmeter sees the same voltage as the element.
A constant resistor is placed inside the ohmmeter: to protect the meter and fix the calibration.
The cell of an ohmmeter must have a constant emf: a changing emf would make the calibration wrong.
The scale of the ohmmeter is not linear and runs in the opposite sense to that of the ammeter: because I = VB/(Rtotal + Rx) is not proportional to Rx, and larger resistance gives smaller current.
📝 Question bank for this point
1 questions linked to this point only, 1 of them with pictures.