Physical quantities

What is a physical quantity?

A physical quantity is a feature of something that can be measured, for example, length, mass or the time interval for a particular event. 

Every physical quantity has a numerical value and a unit.

Large and small quantities are usually expressed in scientific notation, i.e. as a simple number multiplied by a power of ten. Thus, if we have a value of 0.0005, what would 0.0005 be written as?

`0.0005=5xx10^(-4)` 

Explain: Before the whole number, there are four zeros, so we write 5 × 10⁻⁴. The negative sign in the exponent indicates that there are four zeros before the whole number. Conversely, if there is no negative sign, there will be four zeros after the whole number.

Which of the following is the correct expression of 123000000000?

A. `12.3xx10^11`

B. `123xx10^10`

C. `1.23xx10^10`

D. `1.23xx10^11`

The answer is D. 

Explain: After the whole number, there are nine zeros, so we write `123xx10^9`. The positive sign in the exponent indicates that there are nine zeros after the whole number. Conversely, if there is no positive sign, there will be nine zeros before the whole number. However, to find the exponent which is expressed as answer, count the number of time you need to shift the number one digit to the right before the result is less than 10. Thus, 123000000000 needs to be shifted to the right 11 times before the result 1.23 is less than 10, so `1.23xx10^11`

What is needed to accurately represent all physical quantities?

A. A base unit and a number

B. A unit and a number expressed in standard form (scientific notation)

C. A unit and a numerical magnitude

D. An SI unit and a numerical magnitude

The answer is C.

When presenting the result of a measurement of a physical quantity or the solution to a physics problem, we need a numerical value to represent the magnitude of the quantity along with its corresponding unit of measurement.

A. incorrect, we need numerical value instead of number.

B. incorrect, same as A

D. incorrect, not only SI unit could represent unit of measurement.

Which quantity is a physical quantity?

A. Kilogram

B. Kelvin

C. Minute

D. Potential difference

The answer is D.

A physical quantity is a feature of something which can be measured. Every physical quantity has a numerical value and a unit.

A. unit of mass

B. SI unit of temperature

C. unit of time

D. Potential difference is measured in volts

What could not be a measurement of a physical quantity?

A. 10 K

B. 11 `J.N^(-1).m^(-1)`

C. 17 `Pa.m^3.N^(-1)`

D. 25 Tm

The answer is B

A. K is the S.I. unit of temperature.

B.  `frac(J)(N.m)=frac(kg.m.s^-2.m)(kg.m.s^-2.m)`  has no unit, as such, this is not a measure of any physical quantity.

C. `frac(Pa.m^3)(N)=frac((N/m^2)m^3)(N)=m`, so this is the measure of height or distance.

D. It is a measurement of a length because it has a magnitude and a corresponding unit.

Which term represents a physical quantity?

A. Metre

B. Percentage uncertainty

C. Kilogram

D. Spring constant

The answer is D.

A. A metre is a unit

B. Percentage uncertainty is the relative uncertainty multiplied by 100.

C. Kilogram is a unit

D. The spring constant is expressed as `k=|F|/x`. Thus, it has a unit and numerical magnitude and is a measure of the stiffness of the spring.

Which pair of quantities are physical quantities?

A. Charge and ampere

B. Efficiency and kilogram

C. Pascal and strain

D. Period and potential difference

The answer is D.

Remember that the physical quantity should have a unit and a numerical magnitude.

A. Ampere is a unit of electric current

B. Kilogram is a unit of mass

C. Pascal is a unit of pressure

Which rows shows what all physical quantities must have?

The answer is C.

Remember that the physical quantity should have a unit and a numerical magnitude. Only vectors have direction.

Which of the following is the correct expression of 0.000023?

A. `23xx10^(-4)`

B. `230xx10^(-4)`

C. `2.3xx10^(-4)`

D. `2.3xx10^(-5)`

The answer is D

Explain: Before the whole number, there are five zeros, so we write `2.3 × 10^(-5)`. The negative sign in the exponent indicates that there are five zeros before the whole number. Conversely, if there is no negative sign, there will be five zeros after the whole number.