Two wires ' A ' and ' B ' of equal length are connected in left and right gap respectively of meter bridge, null point is obtained at 40 cm, from the left end. Diameters of the wires ' A ' and ' B ' are in the ratio 3: 1 respectively, the ratio of specific resistance of 'A' to that of 'B' is (a) 6: 1 (b) 8: 1 (c) 16: 1 (d) 12: 1

Answer: (a). Balance: (RA)/(RB) = 40/60 = 2/3. R = (ρ L)/(π d²/4) with equal L, so (ρA)/(ρB) = (RA)/(RB)((dA)/(dB))². (ρA)/(ρB) = 2/3 × 9 = 6. So the answer is (a) 6: 1.

Two wires ' A ' and ' B ' of equal length are connected in left and… | MHT CET 2021 (21 Sep, Shift 1)

Q58MHT CET 2021 · 21 SEP · SHIFT 1Medium

Wheatstone Bridge & Metre Bridge

Two wires ' $\mathrm{A}$ ' and ' $\mathrm{B}$ ' of equal length are connected in left and right gap respectively of meter bridge, null point is obtained at $40\text{ cm}$ , from the left end. Diameters of the wires ' $A$ ' and ' $B$ ' are in the ratio $3 : 1$ respectively, the ratio of specific resistance of 'A' to that of 'B' is

Show answer and solution

Answer: (a)

Balance: $\dfrac{R_A}{R_B} = \dfrac{40}{60} = \dfrac{2}{3}$ .
$R = \dfrac{\rho L}{\pi d^2/4}$ with equal $L$ , so $\dfrac{\rho_A}{\rho_B} = \dfrac{R_A}{R_B}\left(\dfrac{d_A}{d_B}\right)^2$ .
$\dfrac{\rho_A}{\rho_B} = \dfrac{2}{3} \times 9 = 6$ .
So the answer is (a) $6 : 1$ .

Report a mistake

Wheatstone Bridge & Metre Bridge question from MHT CET 2021 (21 Sep, Shift 1)

More questions on Wheatstone Bridge & Metre Bridge