The masses of three wires of copper are in the ratio 1:3:5 and lengths

⇦

⇨

The masses of three wires of copper are in the ratio 1:3:5 and lengths are in the ratio 5:3:1. Then the ratio of their electrical resistance are

Options

(a) (1:3:5)
(b) (5:3:1)
(c) (1:15:25)
(d) (125:15:1)

Correct Answer:

(125:15:1)

Explanation:

Let A₁, A₂ and A₃ be the area of cross-section of three wires of copper of masses m₁,m₂ and m₃ and length l₁,l₂ and l₃ respectively.

m₂ = 3m, m₃ = 5m, l₁ = 3l, l₃ = l

Since Mass = Volume density

.·. m = A₁ × 5l × ρ —-(i)

3m = A₂ × 3l × ρ —(ii)

5m = A₃ × 1l × ρ —(iii)

From (i) and (iii), we get

A₂ = 5A₁

From (i) and (iii), we get

A₃ = 25 A₁

.·. R₁ = ρl₁ / A₁ = ρ5l / A₁, R₂ = ρl₂ / A₂ = ρ3l / A₁ = (3 / 25) R₁

R₃ = ρl₃ / A₃ = ρl / 25 A₁ = (R₁ / 125) = 125 : 15 : 1

Related Questions:

1. A carnot engine working between 300 K and 600 K has a work output of 800J per cycle.
2. If the series limit of Lyman series for hydrogen atom is equal to the series limit
3. A light emitting diode(LED) has a voltage drop of 2 volt across it
4. In an AC generator, a coil with N turns, all of the same area A and total resistance R,
5. Two resistors of 6Ω and 9Ω are connected in series to a 120 V source.

Topics: Current Electricity (136)
Subject: Physics (2479)

---

Important MCQs Based on Medical Entrance Examinations To Improve Your NEET Score

18000+ students are using NEETLab to improve their score. What about you?

Solve Previous Year MCQs, Mock Tests, Topicwise Practice Tests, Identify Weak Topics, Formula Flash cards and much more is available in NEETLab Android App to improve your NEET score.

---

Share this page with your friends