$1 \ \mathrm{meter} = c \times (1/299,792,458) \ \mathrm{seconds}$

Question 1

Which of the following best describes the definition of a second in the SI system?

Accepted Answer

The time required for 9,192,631,770 oscillations of the radiation absorbed by a cesium-133 atom.

Question 2

How is the meter currently defined in the SI system?

Accepted Answer

As the distance light travels in a vacuum during $1/299,792,458$ of a second.

Question 3

Which physical constant is used to define the kilogram in the modern SI system?

Accepted Answer

The Planck constant, $h$

Question 4

A scientist wants to measure the time it takes for a chemical reaction to complete. Which SI base unit should they use?

Accepted Answer

Second ($s$)

Question 5

If a laser beam travels in a vacuum for $2.99792458 	imes 10^{-9}$ seconds, how far does it travel?

Accepted Answer

$1$ meter

Question 6

Which of the following is NOT an SI base unit?

Accepted Answer

Joule ($J$)

Question 7

The frequency of the radiation used to define the second is based on which atom?

Accepted Answer

Cesium-133

Question 8

Which SI base unit is used to measure electric current?

Accepted Answer

Ampere ($A$)

Question 9

A student measures the mass of a sample using the SI system. Which definition is most relevant to their measurement?

Accepted Answer

The kilogram is defined by a fixed numerical value of the Planck constant $h = 6.62607015 	imes 10^{-34} \ \mathrm{J \cdot s}$.

Question 10

Which of the following correctly matches the SI base unit with its physical quantity?

Accepted Answer

Candela ($cd$) — luminosity

Question 11

A physicist is calibrating a clock using the SI definition of the second. Which process should they use?

Accepted Answer

Counting the oscillations of a cesium-133 atom's radiation.

Question 12

Which equation represents the relationship used to define the meter in terms of the speed of light?

Accepted Answer

$1 \ \mathrm{meter} = c 	imes (1/299,792,458) \ \mathrm{seconds}$

Question 13

Which of the following statements about SI units is correct?

Accepted Answer

The SI system defines units based on fundamental physical constants.

Question 14

A laboratory uses a cesium atomic clock to synchronize its experiments. What property of cesium-133 is essential for this process?

Accepted Answer

The frequency of its radiation transition

Question 15

Which SI base unit is defined by a fixed numerical value of the Planck constant?

Accepted Answer

Kilogram ($kg$)

Question 16

A student claims that the meter is defined by the length of a metal bar. How would you correct their misconception?

Accepted Answer

Explain that the meter is defined by the distance light travels in a vacuum during $1/299,792,458$ of a second.

Question 17

Which of the following is the correct SI base unit for temperature?

Accepted Answer

Kelvin ($K$)

Question 18

A hospital calibrates its medical equipment using SI units. Which definition of the second should they use?

Accepted Answer

The time required for $9,192,631,770$ oscillations of the radiation absorbed by a cesium-133 atom.

Question 19

Which SI base unit is used to measure the amount of substance?

Accepted Answer

Mole ($mol$)

Fundamental SI Units and Their Definitions in Physics

Study Guide - Practice Questions