SI Units

Question 1

Regarding the base SI units (true or false):

The second is the time taken for light to travel a certain length in a vacuum

Answer 1

False. A second is the duration of a certain number of oscillations of a caesium-133 atom. The description of the metre is based on light travelling in a vacuum.

Question 2

Regarding the base SI units (true or false):

The base unit for weight is the kilogram

Answer 2

False. The kilogram is the base unit for Mass. Weight is not a base unit at all: it is force acting upon mass. Hence, people on the moon have less force, i.e. gravity, acting upon them so they weigh less, even though their mass is exactly the same.

Question 3

Regarding the base SI units (true or false):

The base unit for temperature is the Celsius

Answer 3

False. The base unit for temperature is the Kelvin, which is Celsius minus 273.15.

Question 4

Regarding the base SI units (true or false):

The base unit for length is the metre

Answer 4

True

Question 5

Regarding the base SI units (true or false):

The base unit for electrical current is the volt

Answer 5

False. The base unit for electrical current is the Ampere.

Question 6

Regarding derived and non-SI units (true or false):

Derived units must always be expressed as base units

Answer 6

False. The Pascal, for example, can be expressed as base units (kg/m/s2) or a combination of base and derived units (N/m2).

Question 7

Regarding derived and non-SI units (true or false):

Velocity and speed have the same base units

Answer 7

True. Speed is defined as m.s-1, Velocity is defined as m.s-1 but in a given direction

Question 8

Regarding derived and non-SI units (true or false):

101.3 kPa is equivalent to 760 cm H2O

Answer 8

False. It is equivalent to 760 mmHg. It would be equivalent to 1020 cmH2O.

Question 9

Regarding derived and non-SI units (true or false):

The litre is the SI unit for volume

Answer 9

False. The cubic centimeter is the approved unit, with 1 cm3 being equivalent to 1ml.

Question 10

Regarding the units for pressure (true or false):

The kilopascal is the SI unit for pressure

Answer 10

True. Although the pascal is the actual unit, by using the approved kilo- prefix, it is still classed as an SI unit

Question 11

Regarding the units for pressure (true or false):

10 cmH2O is equivalent to 7.6 mmHg

Answer 11

True

Question 11

Regarding the units for pressure (true or false):

1 Bar is greater than 1 Atmosphere

Answer 11

False. Although, for simplicity, both Bar and atmosphere are considered to have a value of 1, 1 atmosphere = 1.013 Bar.

Question 12

Regarding the units for pressure (true or false):

An ETCO2 of 3.5 kPa is equivalent to 27 mmHg

Answer 12

True.

Question 13

In base units, the pascal is best described as:

A. kg x m2/s2
B. kg x m/s2
C. kg/m/s2
D. m/s
E. kg x m2/s3/A2

Answer 13

C.

A. Incorrect. This is the joule.
B. Incorrect. This is the Newton.
D. Incorrect. This is speed.
E. Incorrect. This is the ohm.