# Civil Engineering - Strength of Materials - Discussion

Discussion Forum : Strength of Materials - Section 1 (Q.No. 34)
34.
The deflection of any rectangular beam simply supported, is
directly proportional to its weight
inversely proportional to its width
inversely proportional to the cube of its depth
directly proportional to the cube of its length
none of these.
Explanation:
No answer description is available. Let's discuss.
Discussion:
42 comments Page 1 of 5.

Rajpal said:   5 months ago
Yes, option E is the right answer.

Mohit said:   12 months ago
D should be the correct answer, width and depth will change about the axis you are considering that is Ixx or Iyy but the length will be the same, so the answer should be option D.

Shahab Mehsood said:   1 year ago
B and C both are correct as I=bh^3/12.
Hence deflection is inversely proportional to the width and cube of the depth of the beam.

Rahim Sayyed said:   2 years ago
Between B &D, D is Power 3 therefore it's a major factor dominating the deflection compare to B. So, D should be the right one.

Dipunku said:   3 years ago
It should be all of these.

VIPIN SAINATH said:   3 years ago
Option C &D is correct because Deflection is inversely proportional to Depth & Moment of Inertia. Deflection is directly proportional to Width and length. When we increase the width area Moment of Inertia reduces and Deflection may also be increased and In case of length, longer spans have high deflection ratio.

U.S.lakshmi said:   3 years ago
The deflection of the beam is directly proportional to (wl^3) and inversely proportional to EIso why is the option choose 'c' and actually option e is all the above I think there is some printing mistake done.

Zia-Ur-Rehman said:   3 years ago
In every equation for rectangular beam, there is a term variable/EI (I= bh^3/12) in the denominator, while the rest of variables change with loading conditions, therefore the given answer is correct.

Niraj Adhikari said:   4 years ago
As we know pure bending formula,

M/I =E/R ( particular).

Where 1/R= deflection.

So deflection is proportion to bending moment and inversely proportion to flexural rigidity (EI) where I for rectangle section is bd^3/12.
Hence, deflection is inversely proportioned to with and also a cube of its depth.

Ajay Desai said:   4 years ago
As per my knowledge, the answer will be (E). Because;

(a) not directly proportional to its weight but the load.
(b) I may be 1/12 db^3.
(c) same as (b).
(d) power of l changes with the load.