Physical Quantities and Units (And Uncertainties)

Question 1

What are the 7 base quantities and their units?

Answer 1

Length ~ m
Mass ~ kg
Time ~ s
Temperature ~ K
Amount of Substance ~ mol
Light intensity ~ Cd
Electric current ~ A

Question 2

Giga

Answer 2

10 power 9

Question 3

Mega

Answer 3

10 power 6

Question 4

Tera

Answer 4

10 power 12

Question 5

Pico

Answer 5

10 power -12

Question 6

Nano

Answer 6

10 power -9

Question 7

Milli

Answer 7

10 power -3

Question 8

Micro

Answer 8

10 power -6

Question 9

Deci

Answer 9

10 power -1

Question 10

Centi

Answer 10

10 power -2

Question 11

Kilo

Answer 11

10 power 3

Question 12

Physical quantity

Answer 12

Any quantity that can be measured

Question 13

Base Quantity

Answer 13

A quantity that cannot be further split up into simpler quantities.

Question 14

Derived Quantity

Answer 14

A derived quantity is formed due to some manipulation of the base quantities.
eg: speed, acceleration etc

Question 15

Precision

Answer 15

Precision measures how close two or more values are to each other (closeness). If a measurement is repeated several times, then they can be described as precise if all the values are similar to each other.

Question 16

Accuracy

Answer 16

How close the measured value is to the actual or true value.

Question 17

Random Error

Answer 17

🔹Random errors are due to unpredictable fluctuations in an instrument’s readings as a result of different factors such as an error caused by the experimenter (eg: parallax error) or by environmental conditions.

🔹This affects the precision of the measurements taken, causing a wider spread of results about the mean value.

🔹To reduce random error: repeat measurements several times and calculate an average from them.

🔹Affects precision.

Question 18

Systematic Error

Answer 18

🔹Systemic errors arise (due to the system) from the use of faulty instruments being used or from flaws in the experimental method.

🔹This type of error is repeated every time the instrument is used or the method is followed which affects the accuracy of all readings obtained.

🔹To reduce systemic errors; the instrument being used should be recalibrated or the technique being used should be readjusted or corrected.

🔹Affects accuracy.

Question 19

How can we reduce Systematic Errors?

Answer 19

Instruments should be recalibrated or the technique being used should be corrected or adjusted.

Question 20

What is a Zero Error?

Answer 20

🔹This is a type of systematic error which occurs when an instrument gives a reading when the true reading is zero.

🔹This introduces a fixed error into the readings which must be accounted for when the results are recorded.

Question 21

What is an uncertainty?

Answer 21

The uncertainty is an estimate of the difference between the measured reading and the true value.

Question 22

Are uncertainties and errors the same?

Answer 22

Uncertainties are not the same as errors

• Errors can be thought of as issues with equipment or methodology that cause a reading to be different from the true value

• The uncertainty is a range of values around a measurement within which the true value is expected to lie, and is an estimate