The question asks about the number of grades concrete is designated into as per Indian Standard (IS) specifications. This is a factual question related to concrete technology and Indian building codes, specifically IS 456:2000.
According to some interpretations and older classifications often referred to in competitive exams, concrete is designated into 7 grades. These typically include M10, M15, M20, M25, M30, M35, and M40. While IS 456:2000 lists a broader range of grades, the option "7 grades" is a commonly accepted answer in the context of such questions.
The question asks about the average life of first-class timber. This is a factual question related to the classification and properties of timber used in construction and engineering. The classification of timber into first, second, and third class is based on its durability and strength, which directly correlates with its expected lifespan.
D) More than 10 years. First-class timber is highly durable and resistant to decay and insects. Its average life is generally considered to be more than 10 years, often extending to 20-30 years or even longer, depending on the species and environmental conditions.
The question asks about the fundamental principle behind the equation of continuity. This equation is a statement about the flow of a fluid and relates the fluid's velocity and cross-sectional area at different points in a flow path.
A) Mass. The equation of continuity is a direct consequence of the principle of conservation of mass. It states that mass cannot be created or destroyed in a closed system, meaning the mass flow rate remains constant along a flow path.
The question asks to identify the instrument used for accurate centering in a plane table survey. Centering is a crucial step in surveying to ensure that the point on the ground is precisely represented on the drawing sheet. We need to evaluate each option based on its function in plane table surveying.
C) Plumbing fork — A plumbing fork, along with a plumb bob, is used to accurately transfer the ground station point to the corresponding point on the drawing sheet, ensuring precise centering of the plane table over the station.
The question asks to identify what a series of closely spaced contour lines represents. Contour lines are lines on a map that connect points of equal elevation. The spacing between these lines indicates the steepness of the slope. We need to understand the relationship between contour line spacing and slope gradient.
A) Steep slope. When contour lines are closely spaced, it signifies that the ground elevation changes rapidly over a short horizontal distance, which is characteristic of a steep slope.
This question tests knowledge about the properties of cement, specifically how its strength changes over time when stored. Cement is a hygroscopic material, meaning it readily absorbs moisture from the atmosphere. This absorption leads to a chemical reaction that affects its quality.
Correct Option: A) Decreases. Due to premature hydration caused by atmospheric moisture absorption during storage, cement loses its reactivity, leading to a reduction in its ultimate strength.
The question asks about the desirable characteristic of a pointer in an indicating instrument. The key factors to consider are inertia, response time, and accuracy. A pointer's mass directly influences its inertia, which in turn affects how quickly and accurately it can settle at a reading.
Correct Option: A) very light
A very light pointer has low inertia, allowing it to respond quickly to changes in the measured quantity and settle at the correct reading without excessive oscillation. This ensures accurate and fast measurements.
This question asks about the common method used for damping in most electrical measuring instruments. Damping is crucial to prevent oscillations of the pointer and allow it to settle quickly at the correct reading.
Correct Option: C) eddy currents
Eddy current damping is the most common and efficient method used in the majority of electrical measuring instruments, particularly in moving coil instruments, due to its effectiveness in providing critical damping without adding significant friction or bulk.
The question asks to classify an ammeter based on its operational principle. We need to understand the different types of instruments in electrical measurements and how an ammeter fits into these classifications.
Correct Option: A) secondary instrument. An ammeter is a secondary instrument because it requires calibration against a standard and its readings are directly indicated on a pre-calibrated scale.
An ammeter is used to measure current in a circuit. To measure a wide range of currents accurately and safely, a shunt resistor is connected in parallel with the galvanometer (the core component of an ammeter). This arrangement allows only a small, proportional part of the total current to pass through the galvanometer, while the majority of the current bypasses it through the shunt.
A) by pass the current
As explained, the shunt is a low-resistance path connected in parallel with the galvanometer. Its main function is to allow the majority of the current to flow through it, thereby bypassing the sensitive galvanometer coil and protecting it from high currents. This also allows the ammeter to measure a wider range of currents.