Timber A has narrower annual rings and more compact medullar rays compared to timber B. Which timber is expected to be stronger and which is expected to have lesser shrinkage respectively?
- AA, ACorrect
- BA, B
- CB, A
- DB, B
Solution
Concept
Closer annual rings in timber signify higher density and strength, as well as reduced shrinkage properties.
Step-by-step solution
1. Understand the characteristics of timber: Narrow annual rings indicate slow growth, high density, and high strength. 2. Medullar rays that are compact and regular also contribute to uniform strength and dimensional stability. 3. Therefore, Timber A is stronger and exhibits lesser shrinkage compared to Timber B.
Explanation
Timber with narrower annual rings indicates slower growth, which generally results in denser, harder, and stronger wood (often called close-grained timber). More compact medullar rays and close grain also result in less moisture movement and lower volumetric shrinkage.
Why the other options are wrong
B: B has wider rings and is weaker with more shrinkage. C: Reversed properties. D: B is assumed stronger, which is incorrect.
Shortcut
Narrow annual rings = Stronger wood & Lesser shrinkage.
Common mistake
Mistaking wide annual rings (fast growth, lower density) for stronger timber.
Correct answer: A) A, A