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Physics > 3.1 Measurements and their errors > Flashcards

3.1 Measurements and their errors Flashcards

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1
Q

What is the SI unit of mass?

A

Kg

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2
Q

What is the SI unit of time?

A

s

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3
Q

What is the SI unit of temperature?

A

K (Kelvin)

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4
Q

What is the SI unit of current?

A

A (Amperes)

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5
Q

What is the SI unit of distance?

A

m

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6
Q

What is the SI unit of quantity of matter?

A

mol

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7
Q

What is the prefix for the magnitude 10^12?

A

T (tera)

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8
Q

What is the prefix for the magnitude 10^9?

A

G (giga)

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9
Q

What is the prefix for the magnitude 10^6?

A

M (mega)

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10
Q

What is the prefix for the magnitude 10^3?

A

k (kilo)

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11
Q

What is the prefix for the magnitude 10^-2?

A

c (centi)

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12
Q

What is the prefix for the magnitude 10^-3?

A

m (milli)

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13
Q

What is the prefix for the magnitude 10^-6?

A

µ (micro)

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14
Q

What is the prefix for the magnitude 10^-9?

A

n (nano)

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15
Q

What is the prefix for the magnitude 10^-12?

A

p (pico)

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16
Q

What is the prefix for the magnitude 10^-15?

A

f (femto)

17
Q

How do you convert J to eV?

A

Divide by e (1.60x10^-19)

18
Q

How do you convert from J to kWh?

A

Divide by 3.6x10^6

19
Q

What are random errors?

A

Errors that affect precision - cause differences in measurements causing a spread around the mean
E.g. electronic noise in the circuit of an electrical instrument

20
Q

How do you reduce random errors?

A
  • Take at least 3 repeats and calculate a mean - can also allow anomalies to be identified and removed respectively
  • Use computers/data loggers/cameras to reduce human error and enable smaller intervals
  • Use appropriate equipment - e.g. a micrometer has a higher resolution (0.1mm) than a ruler (1mm)
21
Q

What are systematic errors?

A

Errors that affect accuracy - occur due to apparatus or faults in the experimental method - cause all results to be too high or too low by the same amount by the same amount each time
E.g. - balance isn’t zeroed properly (zero error) or reading scale at a different angle (parallax error)

22
Q

How do you reduce systematic errors?

A
  • Calibrate apparatus by measuring a known value (e.g. weight 1kg mass on a mass balance), if reading is inaccurate then systematic error is easily identified
  • In radiation experiments correct for background radiation by measuring it beforehand and excluding it from final results
  • Read the meniscus (central curve on the surface of a liquid) at eye level (to reduce parallax error) and use controls in experiments
23
Q

What is precision?

A

How consistent measurements are and if they fluctuate slightly about a mean - this doesn’t indicate the value is accurate

24
Q

What is repeatability?

A

An experiment is repeatable when the original experimenter can redo the experiment with the same equipment and method and get the same results

25
Q

What is reproducibility?

A

When the experiment is redone by a different person or with different techniques and equipment and the same results are found

26
Q

What is resolution?

A

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

27
Q

What is accuracy?

A

How close a measurement is to the true value

28
Q

What is the uncertainty in a reading?

A

± half the smallest division

29
Q

What is the uncertainty in a measurement?

A

At least ± one smallest division

30
Q

What is the uncertainty for repeated data?

A

Mean ± range/2

31
Q

What number of sig figs should uncertainties have?

A

The same as the data

32
Q

How do you combine uncertainties when adding/subtracting data?

A

Add absolute uncertainties

33
Q

How do you combine uncertainties when multiplying/dividing data?

A

Add percentage uncertainties

34
Q

How do you combine uncertainties when raising to a power?

A

Multiply percentage uncertainty by power

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