Electrical Measurements & Measuring Instruments Multiple Choice Questions on “Shunts and Multipliers”.
1. Range of an electrical instrument depends on __________
Clarification: The amount of current safely passing through the coil of the instrument and the spiral springs. This acts as the leads of the current to the instrument. As a result, the range of an electrical instrument depends on the current.
2. Moving coil instruments have a current and voltage rating of __________
a) 100 A and 25 V
b) 50 mA and 50 mV
c) 75 nA and 100 μV
d) 25 μA and 75 V
Clarification: Moving coil instruments are designed to function as Ammeters and Voltmeters. They have a maximum current carrying capacity of 50 mA with a voltage rating of 50 mV.
3. A shunt is a __________
a) very high resistance
b) medium resistance
c) very low resistance
d) high resistance
Clarification: Usually shunt is a very low value of resistance. It is connected in parallel with the ammeter coil. Through this we can extend the range of an ammeter.
4. A shunt can be used to measure large currents.
Clarification: A shunt is normally a very low value of resistance, connected in parallel with the ammeter coil. By making use of a low range ammeter, large current values can be measured through a shunt.
5. Current terminals have a small current capacity.
Clarification: A shunt is normally a very low value of resistance, connected in parallel with the ammeter coil. In a shunt, the current terminals have a large current capacity and are connected in series.
6. Potential terminals have a __________
a) high current capacity
b) low voltage capacity
c) low current capacity
d) high voltage capacity
Clarification: A shunt is normally a very low value of resistance, connected in parallel with the ammeter coil. In a shunt, the potential terminals have a low current carrying capacity. As a result, a low range ammeter is used to measure the large current.
7. In case of AC ammeters, shunts consist of __________
Clarification: AC ammeter shunts comprise of the inductances of the ammeter as well as the shunt. In order to extend the range of an AC ammeter, inductances of the ammeter and the shunt are taken into account.
8. What is the effect of the ammeter range on the shunt resistance?
a) no effect
b) varies by a factor of multiplying factor
c) varies by a factor of the resistance
d) varies by a factor of unity
Clarification: We know that
N = 1 + Ra⁄Rs
where, N is the multiplying factor
Ra is the ammeter resistance
Rs is the shunt resistance
It is clear from the above equation that in order to increase the ammeter range by N times, the shunt resistance is equivalent to 1⁄N-1.
9. A multiplier is __________
Clarification: A multiplier is basically a non-inductive, high resistance that is used to extend the range of a D.C. voltmeter. Multiplier consists of a low range D.C. voltmeter connected in series with it.
10. What is the condition for using a multiplier in A.C. voltmeters?
a) by using ac supply
b) by maintaining a uniform impedance
c) by maintaining a uniform frequency
d) by using a galvanometer
Clarification: A multiplier can be used for A.C. voltmeters. The condition to be satisfied is that the total impedance of the voltmeter and the multiplier circuit must be constant for a wide range of frequencies.