B.Tech Measurements and Instruments Quiz

Define dimension of a physical quantity and hence discuss briefly on the significance of the dimensional equations

Answer explanation

The dimension of a physical quantity expresses its nature in terms of fundamental quantities like mass, length, and time. Dimensional equations help in verifying the correctness of physical formulas and converting units, ensuring consistency in calculations.

Define SI unit and discuss the types of SI units

Answer explanation

SI units are the standard units of measurement in the International System of Units. They include base units (like meter, kilogram) and derived units (like newton, joule) that are used to express various physical quantities.

Automotive sensors need to work in a very demanding environment. Depending on the application, the sensor must function in a temp range of -40oC to 85oC (passenger compartment) or 125oC (engine compartment). Exhaust sensors must withstand temperatures up to 800oC. Sensors also must withstand exposure to gasoline, salt, detergents, and other chemicals. All these requirements must meet at a very low price, as well as with a reliability of a few PPM. In context of the above statement, discuss the need for static and dynamic characteristics of the sensor.

Answer explanation

Static characteristics ensure the sensor operates accurately under extreme conditions, while dynamic characteristics ensure it responds quickly to changes. Both are crucial for reliability and performance in harsh automotive environments.

Derive the dimensional equation for resistance R of a resistor. Hence, check for the dimensional correctness of the expression below, where P,Q, p, q are ratio arm resistances, r is the yoke resistance and R, S are the low resistances values: R = (PS/Q)+qr/(p+q+r){(P/Q}- (p/q)}

Answer explanation

Resistance R has the dimensional formula [M^1 L^2 T^-3 I^-2]. The given expression involves ratios of resistances, which are dimensionless, thus maintaining dimensional consistency. Therefore, the expression is dimensionally correct.

Derive the dimensional equations for absolute permeability μ

Answer explanation

Absolute permeability (μ) is derived from the relationship between magnetic field strength (H) and magnetic flux density (B). Its dimensional equation is [μ] = [M][L]^{-1}[T]^{-2}[I]^{-2}, representing mass, length, time, and electric current.

Given expected voltage value across a resistor is 80V. The measurement is 79V. Calculate, Absolute error % of error Relative accuracy % of accuracy

Answer explanation

Absolute error = |80V - 79V| = 1V. % of error = (1V / 80V) * 100 = 1.25%. Relative accuracy = 100% - 1.25% = 98.75%. Thus, absolute error is 1V, % of error is 1.25%, and % of accuracy is 98.75%.

The value of any particular quantity in SI system of units can be expressed in terms of _______

• 10^6

• 10^m

• 10

• 273.16

The base unit of mass in the SI system is _______

• Gram

• Kilogram

• Pound

• Ounce

The SI unit for measuring temperature is _______

• Fahrenheit

• Celsius

• Kelvin

• Rankine

The standard unit of electric current in the SI system is _______

• Volt

• Ampere

• Ohm

• Watt