A physical quantity is a phyical property of a phenomenon , body, or substance , that can be quantified by measurement.
The magnitude of the components of a vector are to be considered dimensionally distinct. For example , rather than an undifferentiated length unit L, we may represent length in the x direction as `L_(x)`, and so forth. This requirement status ultimately from the requirement that each component of a physically meaningful equation (scaler or vector) must be dimensionally consistent . As as example , suppose we wish to calculate the drift S of a swimmer crossing a river flowing with velocity `V_(x)` and of widht D and he is swimming in direction perpendicular to the river flow with velocity `V_(y)` relation to river, assuming no use of directed lengths, the quantities of interest are then `V_(x),V_(y)` both dimensioned as `(L)/(T)` , S the drift and D width of river both having dimension L. with these four quantities, we may conclude tha the equation for the drift S may be written : `S prop V_(x)^(a)V_(y)^(b)D^(c)`
Or dimensionally `L=((L)/(T))^(a+b)xx(L)^(c)` from which we may deduce that a+b+c=1 and a+b=0, which leaves one of these exponents undetermined. If, however, we use directed length dimensions, then `V_(x)` will be dimensioned as `(L_(x))/(T), V_(y)` as `(L_(y))/(T)`, S as `L_(x)" and " D as L_(y)`. The dimensional equation becomes : `L_(x)=((L_(x))/(T))^(a) ((L_(y))/(T))^(b)(L_(y))^(c)` and we may solve completely as a=1,b=-1 and c=1. The increase in deductive power gained by the use of directed length dimensions is apparent.
Which of the following is not a physical quantity

Options

A. Height of a boy
B. Weight of a boy
C. Fever of a boy
D. Speed of a running boy

Answer

To determine which of the following is not a physical quantity, we need to analyze each option based on the definition of a physical quantity. A physical quantity is a property that can be quantified by measurement.

### Step-by-Step Solution:

1. **Identify the Options**: We need to examine the given options to identify which one cannot be measured objectively.

2. **Examine Each Option**:
- **Height of a Boy**: This can be measured using a ruler or measuring tape, typically in meters or centimeters. Thus, it is a physical quantity.
- **Weight of a Boy**: This can be measured using a weighing scale, typically in Newtons or kilograms. Therefore, it is also a physical quantity.
- **Speed of a Running Boy**: This can be measured in meters per second or kilometers per hour. Hence, it is a physical quantity.
- **Fever of a Boy**: While fever can be associated with an increase in body temperature, it does not have a direct measurement unit. We can measure temperature in degrees Celsius or Fahrenheit, but "fever" itself does not have a standard unit of measurement.

3. **Conclusion**: Based on the analysis, the option that cannot be measured objectively is "Fever of a Boy." Thus, it is not a physical quantity.

### Final Answer:
**Fever of a Boy is not a physical quantity.**