KVPY 2019 SA Exam Previous Papers

Question : 68 of 80

Marks: +1, -0

A student uses the resistance of a known resistor (1Ω) to calibrate a voltmeter and an ammeter using thecircuits shown below. The student measures the ratio of the voltage to current to be 1 × 10

^3

Ω in circuit (a)and 0.999 Ω in circuit (b). From these measurements, the resistances (in Ω) of the voltmeter and ammeterare found to be close to :

10 $^{2}$ and 10 $^{–2}$
10 $^{3}$ and 10 $^{–3}$
10 $^{–2}$ and 10 $^{2}$
10 $^{–3}$ and 10 $^{3}$

Validate

Solution:

case –a

R_v =

Resistance of voltmeter

R_A =

Resistance of ammeter

V/A={IR_v}/(I/{1+R_A})

= R_v (1 + R_A) = 1000

…(i)
Case – b

V/A={ (I/{1+R_v})R_v}/I

= R_v/ {R_v+1 } = 0.999

R_v = 0.999 (1 + R_v )

⇒

R_v = 999Ω

From (i)

R_A = 10^{–3}Ω

Go to Question:

Prev Question

Next Question