Question

Power is measured with an a.c. potentiometer. The voltage across a 0.1Ω standard resistance connected in series with the load is 0.35 – j0.10V. The voltage across 300:1 potential divider connected to the supply is 0.8 + j0.15V. Determine the power consumed by the load and the power factor​

Answer 1

Answer:

Measurement is the act, or the result, of a quantitative comparison between a given

quantity and a quantity of the same kind chosen as a unit. The result of the measurement is

expressed by a pointer deflection over a predefined scale or a number representing the

ratio between the unknown quantity and the standard. A standard is defined as the physical

personification of the unit of measurement or its submultiple or multiple values. The

device or instrument used for comparing the unknown quantity with the unit of

measurement or a standard quantity is called a measuring instrument. The value of the

unknown quantity can be measured by direct or indirect methods. In direct measurement

methods, the unknown quantity is measured directly instead of comparing it with a

standard. Examples of direct measurement are current by ammeter, voltage by voltmeter,

resistance by ohmmeter, power by wattmeter, etc. In indirect measurement methods, the

value of the unknown quantity is determined by measuring the functionally related

quantity and calculating the desired quantity rather than measuring it directly. Suppose the

resistance as (R) of a conductor can be measured by measuring the voltage drop across the

conductor and dividing the voltage (V) by the current (I) through the conductors, by

Ohm’s

1.2 FUNDAMENTAL AND DERIVED UNITS

At the time of measuring a physical quantity, we must express the magnitude of that

quantity in terms of a unit and a numerical multiplier, i.e.,

Magnitude of a physical quantity = (Numerical ratio) × (Unit)

The numerical ratio is the number of times the unit occurs in any given amount of the

same quantity and, therefore, is called the number of measures. The numerical ratio may

be called numerical multiplier. However, in measurements, we are concerned with a large

number of quantities which are related to each other, through established physical

equations, and therefore the choice of size of units of these quantities cannot be done

arbitrarily and independently. In this way, we can avoid the use of awkward numerical

constants when we express a quantity of one kind which has been derived from

measurement of another quantity.

In science and engineering, two kinds of units are used:

• Fundamental units