Measurement of Charge Sensitivities

The charge passing through a B.G., is given by
q = T ___c___ θ₁ (1 + λ/2) = Kθ₁ ( 1 + λ/2)
     2π___NBA
Here K is charge sensitiveness of figure of merit of the galvanometer.

The charge that should calculate through the coil to produce an undamped throw 1mm in the spot of light on a scale placed at a distance of 1 meter from the mirror is called the charge sensitiveness K of the ballistic galvanometer.

Two resistance boxes P and Q and a key K are connected in series with an accumulator of emf E. A capacitor of known capacitance C is connected to P through the vibrator V and charging terminal Ch of the charge-discharge key. The capacitor is charged with the p.d. across P. The charge on the capacitor can be discharged through the B.G. included in the circuit through the vibrator and discharge terminal of the charge-discharge key. A commutator Cr is included in the circuit to reverse the charge in the B.G.

1000Ω in P and 9000Ω in Q are included. The capacitor is charged and immediately discharged through the B.G. The first throw θ₁ is noted. The experiment is repeated with P = 2000Ω, 3000Ω etc., keeping P + Q = 10,000Ω.Mean value of P/ θ1 is calculated.
Let the capacitor of the capacitor be CμF.

Charge on the capacitor q = ___EP___ x C μC.
________________________ P   + Q
This charge produce a throw θ₁.

Undamped throw θ = θ₁ (1 + ½ λ)

Charge required to produce unit deflection = K.
    : . K θ₁ (1 + ½ λ) = ___EP___ x C
_________________(P    + Q)

or____K = ___EC___ x ___P___ μC / div.
___________P + Q        θ₁ (1 ½ λ)

The value of λ is obtained by observing the first throw θ1 and then the eleventh throw θ11 and using the relation
      λ = 1 log_e θ₁ = 1 x 2.3026 x log₁₀ θ₁
_____10     θ₁₁   10 ____________θ₁₁



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