Measurements and their errors

Question 1

What are the six SI units?

Answer 1

mass (m)- Kg
length (l) - m (metres)
Time (t) - s (seconds)
Amount of substance(n) - mol (moles)
Temperature (t) - K (kelvin)
Electric current (I) - A (amperes)

Question 2

How can SI unit quantities be derived?

Answer 2

By there equation. e.g. F= ma = Kg*ms^-2 so N = Kgms^2

Question 3

What is the multiplier of Tera(T)

Answer 3

*10^12

Question 4

What is the multiplier of Giga(G)

Answer 4

*10^9

Question 5

What is the multiplier of Mega(M)

Answer 5

*10^6

Question 6

What is the multiplier of Kilo(K)

Answer 6

*10^3

Question 7

What is the multiplier of centi(c)

Answer 7

*10^-2

Question 8

What is the multiplier of milli(m)

Answer 8

*10^-3

Question 9

What is the multiplier of micro(µ)

Answer 9

*10^-6

Question 10

What is the multiplier of Nano(n)

Answer 10

*10^-9

Question 11

What is the multiplier of pico(p)

Answer 11

*10^-12

Question 12

What is the multiplier of Femto(f)

Answer 12

*10^-15

Question 13

What does 1eV equal in joules?

Answer 13

1.6x10^-19J

Question 14

How do u convert from eV to J

Answer 14

times by 1.6x10^-19

Question 15

How do u convert from J to eV

Answer 15

divide by 1.6x10^-19

Question 16

what is 1 KW in Js^-1?

Answer 16

1000 Js^-1

Question 17

How do you convert 1 KWh to J?

Answer 17

do 1000*3600 = 3.6x10^6 because 1 kwh is 1000js^-1 and 1 hour is 3600 seconds.

Question 18

What do random errors affect?

Answer 18

precision

Question 19

What three things can you do to reduce random errors?

Answer 19

• Take at least three repeats and calculate a mean this allows anomalies to be identified
• Use computers/data logger/cameras to reduce human error and enable smaller intervals
• Use appropriate equipment, for example a micrometre has a higher resolution (0.1mm) than a ruler(1 mm)

Question 20

What do systematic errors affect?

Answer 20

accuracy

Question 21

What three ways reduce systematic errors?

Answer 21

• calibrate apparatus by measuring a know value, if reading is inaccurate then their is a systematic error
• In radiation experiments correct for background radiation by measuring it before hand and excluding it from final results
  -Read meniscus at eye level (to reduce parallax error) and use controls in experiments

Question 22

define precision

Answer 22

Precise measurements are consistent, they fluctuate slightly about the mean value - this doesn’t indicate the value is accurate

Question 23

define repeatability

Answer 23

If the original experimenter can redo the experiment with the same equipment and method then get the same results its repeatable.

Question 24

define reproducibility

Answer 24

If the experiment is redone by a different person or with different techniques and equipment and the same results are found, it is reproducible

Question 25

define resolution

Answer 25

The smallest change in the quantity being measured that gives a recognisable change in reading

Question 26

define accuracy

Answer 26

A measurement close to the true value is accurate

Question 27

What is the uncertainty of a measurement?

Answer 27

Is the bounds within which the true value can be expected to lie.

Question 28

What is absolute uncertainty?

Answer 28

Uncertainty is given as a fixed quantity e.g. 7±0.6 V

Question 29

What is fractional uncertainty?

Answer 29

Uncertainty as a fraction of the measurement e.g. 7±3/35 V

Question 30

What is percentage uncertainty?

Answer 30

Uncertainty as a percentage measurement e.g. 7±8.6%

Question 31

How can you reduce percentage and fractional uncertainties?

Answer 31

measure larger quantities

Question 32

What is a reading?

Answer 32

when one value is found

Question 33

What is a measurement?

Answer 33

When the difference between 2 readings is found.

Question 34

What is the uncertainty in a reading?

Answer 34

± half the smallest division

Question 35

What is the uncertainty in a measurement?

Answer 35

at least ± smallest division