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. Water rises in a vertical capillary tube up to a height of 2.0 cm.
2. In the Young’s modulus experiment, if length of wire and radius both are doubled,
3. Which of the following is not a transverse wave?
4. A bus is moving with a speed of 10 ms⁻¹ on a straight road
5. A stone is tied to a string of length l and whirled in a vertical circle with the other end

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