Question 1. Consider a 29 galvanometer having a 330 A sensitivity. Find the resi

Question

Question 1. Consider a 29 galvanometer having a 330 A sensitivity. Find the resistance that must be placed in parallel with the galvonometer in to allow it to be used as an ammeter with a 10.0 A full-scale reading.

Question 2. A certain ammeter has a resistance of 2.5 × 10-5 on a scale which reads up to 3.4 A, and contains a 9.5- galvanometer. What is the sensitivity of the galvanometer, in microamperes?

Question 3. Consider an unknown dry cell for which a potentiometer is balanced when the variable resistance is Rx = 1.65 , while an alkaline standard cell with an emf of 1.15 V requires Rs = 1.248 to balance the potentiometer. Calculate the emf of the dry cell, in volts.

Explanation / Answer

1. given, senstivity of galvanometer = S = 330 uA

now, S = dA/d(theta) = 330 uA

resistance, r = 29 ohms

resistance in parallel = R

now, galvanometer full scale reading = 100*S = 330,00 = 0.03 A

hence

when using for full 10 A raintg, 0.03 A must pass through the galvanometer

hence

9.97 A mucht pass through resistnace

hence

0.03*29 = 9.97*R

R = 0.0872617 ohm

2. r = 2.5*10^-5 ohm

I = 3.4 A

R = 9.5 ohm

hence

maximum current in galvanometer = i

hence

iR = (I - i)r

i = Ir/(r + R)

i = 8.94*10^-6 A

hence

senstivity = i/1000 = 8.94*10^-9 A

3. EMF of dry cell = V

then

V/Rx = 1.15/Rs

hence

V = 1.52 V

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