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. When photons of energy hν fall on an aluminium plate (of work function E₀),
2. An Electric charge does not have which of the following properties?
3. An electric dipole of dipole moment p is aligned parallel to a uniform electric field E
4. A 1m long wire of diameter 0.31 mm has a resistance of 4.2Ω. If it is replaced by
5. Alternating current cannot be measured by D.C Ammeter because

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