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In the resonant frequency method, the dynamic modulus of elasticity of a concrete specimen is given by Ed = 4 × 10⁻¹² × n² × L² × ρ (N/mm²). In this expression, n is the:
Answer & Solution
Correct answer: D.
1. The resonant frequency method excites the specimen until it vibrates at its first natural frequency.
2. In the formula, ρ is the density and L is the specimen length, while n is the fundamental frequency in Hz.
3. The variable frequency oscillator covers a range of 100 Hz to 10,000 Hz to bracket the fundamental.
4. Substituting n, L and ρ yields Ed in N/mm².
5. The other interpretations do not match the symbol meanings stated in the unit.
_Source: IGNOU ET-522 Concrete Technology, Block 2 Unit 9 "Testing of Concrete"._
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