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When an electric current flows through it, the magnetic needle tends to move at right angles to the conductor, such that its direction is parallel to the lines of induction around the conductor and its north pole points in the direction of the lines of induction. A sort of ammeter is one that has a galvanometer. It’s a tool for detecting and measuring electric current.
A moving coil galvanometer is an electromagnetic device that measures the amount of current flowing via a small circuit. A coil, a permanent horse-shoe magnet, a soft iron core, a pointer, a pivoting spring, a non-metallic frame, and a scale are all part of it. A sort of ammeter is one that has a galvanometer. Because the magnetic needle’s orientation is at right angle to the lines of induction that run around it, and its north pole points in the direction of the lines of induction, when a current flows through a circuit, the magnetic needle rotates at right angles to the circuit.
1. Why is a moving coil galvanometer used?
a) Measurement of voltage only
b) Measurement of resistance
c) Measurement of small currents
d) Measurement of electric field
Answer: c) Measurement of small currents
The Moving Coil Galvanometer is a device for measuring and detecting current. It’s a sensitive device capable of detecting currents as low as a few microamperes. It was created in the 1800s by Johann Schweigger.
2. Which of the following expressions represents the galvanometer constant?
a) G = kNAB
b) G = k × NAB
c) G = NABk
d) 1G = kNAB
Answer: a) G = kNAB
The current (I) that passes through a moving coil galvanometer is directly proportional to its deflection (), i.e.
I = Gθ
Where G = kNAB ➔ Galvanometer constant
N = number of turns in the coil; A = area of coil; B = strength of the magnetic field; k = The spring’s torsional constant, which means it restores torque per unit twist.
3. Identify the correct statement.
a) An ammeter is a device that measures the potential difference between two elements in a circuit.
b) A voltmeter is a device that measures current in a circuit.
c) The constant of a galvanometer has no dimensions.
d) The exact inverse of the galvanometer constant is used to express current sensitivity.
Answer: d) The exact inverse of the galvanometer constant is used to express current sensitivity.
The deflection produced in the galvanometer when unit current flows through it is known as current sensitivity.
4. Current sensitivity and voltage sensitivity are linked.
a) True
b) False
Answer: a) True
Voltage and current sensitivity are, in fact, linked.
Current sensitivity Is = NAB/k ;
Voltage sensitivity = θ/V = θ/IR = NAB/Kr;
Therefore, voltage sensitivity ➔ Vs = (1/R) × Is.
5. How does a galvanometer become an ammeter?
a) By wiring a high resistance shunt to the galvanometer in parallel
b) By connecting a low resistance shunt to the galvanometer in parallel
c) A high resistance shunt is connected in series with the galvanometer.
d) A low resistance shunt is connected in series with the galvanometer.
Answer: b) By connecting a low resistance shunt to the galvanometer in parallel
By connecting a suitable low resistance S termed shunt in parallel to a galvanometer, it can be transformed into an ammeter of a particular range.
6. How does a galvanometer become a voltmeter?
a) By connecting a high resistance multiplier to the galvanometer in parallel
b) By connecting a low resistance multiplier to the galvanometer in parallel
c) A low resistance multiplier is connected in series with the galvanometer
d) A high resistance multiplier is connected in series with the galvanometer.
Answer: d) A high resistance multiplier is connected in series with the galvanometer.
By connecting a high resistance called a multiplier in series with a galvanometer, it can be transformed into a voltmeter of a specific range.
7. What should the value of the ammeter’s shunt resistance be in order to improve its range?
a) S = (n – 1) G
b) S = (n – 1)/G
c) S = G/(n–1)
d) S = G/(n+1)
Answer: c) S = G/(n–1)
The value of shunt resistance to be connected in parallel to enhance the range of an ammeter n times is provided by:
S = G/(n–1).
8. An ideal ammeter has infinite resistance and an ideal voltmeter has zero resistance.
a) True
b) False
Answer: b) False
Explanation: An ammeter is a low-resistance device that is constantly linked to the circuit in series. The resistance of a perfect ammeter is zero. The voltmeter is a high-resistance instrument that is always connected in parallel with the circuit part that will be used to detect the potential difference. A perfect voltmeter has an infinite resistance.
10. A galvanometer has a 10 ohm resistance and a full scale deflection of 5 milli amperes. What is the resistance value that should be linked in series with it to allow it to read 2V?
a) 20 Ω
b) 10 Ω
c) 40 Ω
d) 30 Ω
Answer: d) 30 Ω
In this scenario: G = 10 Ω; V = 2 V; Ig = 0.05 A,
The required equation ➔ Ig = V/(R+G) ,
0.05 = 2/(R+10)
(R + 10) = 2/0.05 = 200/5 = 40
R = 40 – 10 R = 30 Ω.
11. If a galvanometer has a resistance of 50 and can only flow 0.05A current through it, what is the value of the shunt resistance (S) required? The ammeter range has been increased to 20 amps.
a) 0.120 Ω
b) 0.125 Ω
c) 0.130 Ω
d) 0.145 Ω
Answer: b) 0.125 Ω
In this scenario: Ig= 0.05 A; G = 50 Ω; I = 20 ARequired equation ➔ S = Ig× G/(I–Ig)
S = 0.05×50/(20–0.05)
S = 2.5/19.95 S = 0.125 Ω
As a result, 0.125 Ω shunt resistance is required.
12. The current running through a galvanometer is 30 milliamperes, the resistance of the galvanometer is 50 milliamperes, and the galvanometer is linked to a shunt of one milliamperes. What is the maximum current that this ammeter can measure?
a) 1.53 A
b) 15.3 A
c) 0.153 A
d) 153 A
Answer: a) 1.53 A
In this scenario, Ig = 30 mA = 0.03 A; S = 1 Ω; G = 50 Ω
Required equation ➔ Maximum current (I) = [(S+G)/S] × Ig
I = [(50+1)/1] × 0.03I = 51 × 0.03I = 1.53 A.
