Working Formula – All Experiments
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Working Formula
G = SR / (R − S)
Meaning of Symbols
G is galvanometer resistance, R is series resistance, and S is shunt resistance.
Example Question
During the half-deflection experiment, a series resistance R = 30 Ω and shunt resistance S = 10 Ω are used. Determine the galvanometer resistance G.
Given
- R = 30 Ω
- S = 10 Ω
Solution
G = SR / (R − S)
G = (10 × 30) / (30 − 10)
G = 300 / 20
Final Answer
G = 15 Ω
Try It Yourself
If R = 40 Ω and S = 10 Ω, determine G.
Working Formula
X / R = l / (100 − l)
Meaning of Symbols
X is unknown resistance, R is known resistance, and l is the balance length in cm.
Example Question
In a meter bridge, the known resistance is R = 4 Ω and the balance point is l = 40 cm from the left end. Calculate the unknown resistance X.
Given
- R = 4 Ω
- l = 40 cm
Solution
X / R = l / (100 − l)
X / 4 = 40 / (100 − 40)
X = 4 × 40 / 60 = 160 / 60
Final Answer
X = 2.67 Ω (approximately)
Try It Yourself
If R = 6 Ω and l = 25 cm, determine X.
Working Formula
X = (P / Q) × R
Meaning of Symbols
X is unknown resistance, R is standard resistance, and P and Q are ratio arms.
Example Question
In a Post Office Box, P, Q and R are given. Determine the unknown resistance X.
Given
- P = 2
- Q = 1
- R = 5 Ω
Solution
X = (P / Q) × R
X = (2 / 1) × 5
X = 2 × 5
Final Answer
X = 10 Ω
Try It Yourself
If P = 3, Q = 2 and R = 4 Ω, determine X.