The question asks about the characteristic of a "sound" cement sample, specifically what free component it should not contain. This relates to the properties and composition of cement, particularly concerning its stability and performance.
A) Lime — The presence of free lime in cement leads to unsoundness due to its slow hydration and consequent expansion, which causes cracking in hardened concrete.
The question asks about the approximate ratio of the tensile strength of concrete to its compressive strength. Concrete is known to be strong in compression but weak in tension. We need to recall the typical percentage range for this relationship.
where \(f_r\) is the modulus of rupture in MPa and \(f_{ck}\) is the characteristic compressive strength of concrete in MPa. For a typical concrete grade like M20, \(f_{ck} = 20 \text{ MPa}\). Then,
\[ f_r = 0.7 \sqrt{20} \approx 0.7 \times 4.47 \approx 3.13 \text{ MPa} \]The direct tensile strength is even lower, typically about 0.5 to 0.7 times the flexural tensile strength. So, for M20 concrete, direct tensile strength would be approximately \(0.5 \times 3.13 = 1.565 \text{ MPa}\) to \(0.7 \times 3.13 = 2.191 \text{ MPa}\).
Comparing this to the compressive strength of 20 MPa:
This range clearly indicates that the tensile strength is around 10% of the compressive strength.
Correct Option: C) 10% — The tensile strength of concrete is generally considered to be about 7% to 15% of its compressive strength. 10% is a widely accepted and good approximation for this ratio.
The question asks about the nature of eddy viscosity in turbulent flow. We need to understand what eddy viscosity represents and how it differs from molecular viscosity.
Correct Option: C) Dependent on the flow
Eddy viscosity is a concept introduced to model the apparent increase in viscosity due to turbulent mixing. It is not a fluid property but rather a characteristic of the turbulent flow itself, varying with the flow conditions and location within the flow field.
The question asks to identify the type of surveying that requires the least amount of office work. This relates to how data is collected, processed, and plotted in different surveying methods.
Correct Option: C) Plane table surveying. This method involves plotting the survey data directly in the field, thus minimizing the amount of office work required for plotting and calculations.
The question asks for the definition of a specific soil property based on the ratio of the volume of voids to the total volume of the soil mass. We need to recall the standard definitions of various soil mechanics terms related to volume relationships.
B) Porosity is defined as the ratio of the volume of voids (\(V_v\)) to the total volume of the soil mass (\(V\)).
\[ n = \frac{V_v}{V} \]This directly corresponds to the description in the question.
The question asks to identify the purest form of iron among the given options. Purity in this context refers to the lowest carbon content and minimal impurities.
B) Wrought iron is the purest form of iron among the given options, characterized by its very low carbon content (typically less than 0.08%) and minimal impurities.
The question asks to identify the commonly used type of instrument for measurements in power systems. Power systems primarily deal with AC quantities (alternating current and voltage). Therefore, the instruments used must be capable of accurately measuring AC parameters.
A) induction — Induction type instruments are widely used in power systems for measuring AC quantities, particularly power (wattmeters) and energy (energy meters). They are specifically designed for AC operation and provide accurate readings for these parameters.
The question asks why the damping of a ballistic galvanometer is kept small. A ballistic galvanometer is designed to measure the total charge passed through it, which is proportional to the first maximum deflection. To achieve an accurate measurement of this charge, it is crucial to maximize the initial swing.
A) get first deflection large — By keeping damping small, the energy loss during the initial swing is minimized, allowing the galvanometer to achieve a larger first maximum deflection. This larger deflection is directly proportional to the charge being measured, thus providing a more accurate and sensitive measurement.
The question asks about the type of error that a rectifier instrument is NOT free from. Rectifier instruments are used to measure AC quantities by converting them to DC. We need to analyze the characteristics of rectifier instruments and their susceptibility to various errors.
Considering the inherent limitations, frequency dependence of rectifier components is a significant source of error that is difficult to completely eliminate, making the instrument not free from frequency error.
C) frequency error. Rectifier instruments use diodes, which have frequency-dependent characteristics (e.g., reverse recovery time, junction capacitance). As the frequency of the AC signal changes, the efficiency of rectification and the overall impedance of the circuit can change, leading to inaccurate readings. Therefore, rectifier instruments are inherently susceptible to frequency errors, especially at higher frequencies.
The question asks to identify the type of ammeter used for measuring alternating current (AC). We need to understand the working principles of different ammeter types and their suitability for AC measurements.
A) induction ammeter — Induction type instruments are specifically designed to measure alternating current (AC) based on the principle of electromagnetic induction. They provide a reading proportional to the RMS value of the AC.