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PMT AQA A-Level Physics > 1.1 Measurements and Their Errors > Flashcards

1.1 Measurements and Their Errors Flashcards

1
Q

What are SI units?

A

Fundamental (base) units of physical quantities.

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2
Q

What is the SI unit of mass?

A

Kg (kilogram).

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3
Q

What physical quantity is measured in mol?

A

Amount of substance.

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4
Q

What is the SI unit of current?

A

Amperes (A).

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5
Q

Is the SI unit for temperature ℃ or K?

A

K (kelvin) as this is the absolute scale.

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6
Q

What is the SI unit of length?

A

Metres (m).

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7
Q

What quantity is measured in seconds?

A

Time.

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8
Q

Are Newtons (N) an SI unit?

A

No, newtons are not fundamental, the SI units for force are kgms^-2.

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9
Q

Derive the SI units of energy.

A

Kinetic energy = ½ x mass x velocity squared
Units = kg x (m/s) x (m/s) = kgm^2s^-2.

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10
Q

Derive the SI units of force.

A

Force = mass x acceleration Units = kg x ms^-2 = kgms^-2.

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11
Q

Express 60TΩ in standard form.

A

6 x 10^13
(T is tera and the multiplier is 10^12).

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12
Q

Write 0.000003m with a suitable prefix.

A

3µm.

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13
Q

What is the actual value of 8MΩ?

A

8,000,000Ω or 8x10^6Ω.

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14
Q

What is 6000pF in nF?

A

6nF as 1 nano unit is 1000 pico units.

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15
Q

What multiplier is associated with the prefix kilo (k)?

A

1000 (10^3).

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16
Q

What multiplier is associated with the prefix femto (f)?

A

10^-15.

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17
Q

Express 7GΩ in standard form.

A

7 x 10^9 Ω.

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18
Q

What is 1 eV in J?

A

1eV= 1.6 x 10^-19 J.

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19
Q

Express 6kWh in joules.

A

6 kWh = 6000 x 3600 = 21.6 x 10^6 J = 21.6 MJ.

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20
Q

Convert 6.6pJ to eV.

A

6.6pJ=4.1 x 10^7 eV (2sf) = 41MeV.

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21
Q

What is a random error?

A

An error that affects precision and cannot be completely removed, it causes differences in measurements.

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22
Q

What is a systematic error?

A

An error that affects accuracy and occurs due to faults in equipment or experimental method, causing the result to be too large/small by the same amount each time.

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23
Q

What are 3 ways to reduce random error?

A
  • Take at least 3 repeats and calculate a mean.
  • Use a computer or a data logger.
  • Use higher resolution equipment.
24
Q

A mass balance reads 1004 g when a 1kg mass is placed on it, is this a random or systematic error?

A

Systematic as the reading is too high by 4g each time.

25
Q

State a cause of parallax error.

A

Reading a scale at a different angle each time, to correct this you should read scales at eye level to reduce parallax error.

26
Q

How can systematic error be reduced?

A

Calibrate apparatus before using e.g. zero the balance when it is empty.

27
Q

Is electronic noise in the circuit of an ammeter random error or systematic error?

A

It is a random error as it will cause fluctuations in readings that affect precision and it cannot be removed.

28
Q

Why should you measure background radiation before measuring the radioactivity of a source?

A

So that only the source’s radioactivity is measured, by accounting for background radiation systematic error is reduced.

29
Q

What is precision?

A

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

30
Q

What is repeatability?

A

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

31
Q

What is reproducibility?

A

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

32
Q

What is meant by resolution?

A

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

33
Q

What is meant if a value is accurate?

A

If the value is close to the true value.

34
Q

What is absolute uncertainty?

A

Uncertainty given as a fixed quantity e.g. 7 +/- 0.6 V.

35
Q

What is the percentage uncertainty in 17 +/- 3 A?

A

3/17 x 100 = 17.647 % = 18 % (2sf).

36
Q

What is the fractional uncertainty of 8 +/- 0.5 m?

A

0.5/8 = 1/16 (0.0625).

37
Q

How can percentage and fractional uncertainty be reduced?

A

Measure larger quantities e.g. a longer rope will have a smaller percentage uncertainty than a shorter one.

38
Q

The time for 10 swings of a pendulum is 13 +/- 0.3s, what is the time and uncertainty for 1 swing?

A

1 swing = 1.3s Uncertainty = 0.03 s Time = 1.3 +/- 0.03 s.

39
Q

What is the difference between a reading and a measurement?

A

Readings are when one value is found, measurements are when the difference between 2 readings is found.

40
Q

What is the uncertainty of a thermometer whose smallest division is 5℃?

A

The uncertainty is ± 2.5 ℃.

41
Q

What is the percentage uncertainty in the measurement of a 2cm line?

A

2 ± 5% cm.

42
Q

What is the uncertainty in the charge of an electron (1.6 x 10^-19C)?

A

1.6 x 10^-19 ± 0.1 x 10^-19 C.

43
Q

The times for a ball to drop are measured as 3.2s, 3.6s, and 3.1s. Find the mean and absolute uncertainty of these times.

A

Mean: 3.3 s, Uncertainty = 0.25, = 3.3 ± 0.3s.

44
Q

What is wrong with writing 7±0.673 V?

A

The uncertainty should be the same number of significant figures as the data ie. 7± 0.7V.

45
Q

A thermometer with an uncertainty of 0.5 K shows the temperature of water falling from 298±0.5 K to 273±0.5K, what is the difference in temperature and the uncertainty in this difference?

A

Difference = 25±1 K.

46
Q

A force of 91±3 N is applied to a mass of 7±0.2 kg, what is the acceleration of the mass?

A

a = 13 ± 6.2%.

47
Q

The radius of a circle is 50.3 cm, what is the percentage uncertainty in the area of the circle?

A

Percentage uncertainty in area = 12%.

48
Q

When drawing a line of best fit on a graph with error bars what must you do?

A

Make sure the line of best fit goes through all the error bars.

49
Q

How do you find the uncertainty in the gradient of a line of best fit?

A

Draw a steepest or shallowest line of worst fit, calculate the gradient difference.

50
Q

How can you find the percentage uncertainty in the gradient of a line of best fit?

A

Percentage uncertainty = | best gradient - worst gradient | / best gradient x 100.

51
Q

How do you work out the uncertainty in the y-intercept of a line of best fit?

A

Uncertainty = | best y-intercept - worst y-intercept |.

52
Q

How do you find the percentage uncertainty in a y intercept?

A

percentage uncertainty = | best y-intercept - worst y-intercept | / best y intercept x 100.

53
Q

What is an order of magnitude?

A

Powers of ten which describe the size of an object.

54
Q

What is the order of magnitude for the diameter of a nucleus?

A

10^-15.

55
Q

What is estimation?

A

A skill physicists must use to approximate values of physical quantities.

56
Q

What is 9.71 x 10^-21 to the nearest order of magnitude?

A

1x10^-20 to 1sf.

PMT AQA A-Level Physics (2 decks)

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