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9749 H2 Physics > Chapter1: Measurement > Flashcards

Chapter1: Measurement Flashcards

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1
Q

Base qty: mass
What’s its base unit?

A

Kilogram, kg

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2
Q

Base qty: length
What’s its base unit?

A

Metre, m

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3
Q

Base qty: time
What’s its base unit?

A

Second, s

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4
Q

Base qty: thermodynamic temperature
What’s its base unit?

A

Kelvin, K

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5
Q

Base qty: electric current
What’s its base unit?

A

Ampere, A

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6
Q

Base qty: amount of substance
What’s its base unit?

A

Mole, mol

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7
Q

Symbol for qty is x, what is the unit of the qty?

A

[x]

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8
Q

What are qtys with no base units?

A

Dimensionless qtys

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9
Q

What type of eqns are definitely wrong?

A

Eqns that are not homogenous

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10
Q

Eqns that are homogeneous may or may not be correct. Explain why.

A

There is:
Presence / absence of dimensionless constant
Incorrect coefficient
Presence of extra item(s) / missing item(s)

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11
Q

The symbol T represents:

A

10^12

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12
Q

The symbol G represents:

A

10^9

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13
Q

The symbol M represents:

A

10^6

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14
Q

The symbol k represents:

A

10^3

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15
Q

The symbol d represents:

A

10^-1

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16
Q

The symbol c represents:

A

10^-2

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17
Q

The symbol m represents:

A

10^-3

18
Q

The symbol µ represents:

A

10^-6

19
Q

The symbol n represents:

A

10^-9

20
Q

The symbol p represents:

A

10^-12

21
Q

Define systematic error.

A

A systematic error is one that causes measurements to have a constant magnitude above or below true value of the measured qty. (either always positive or always negative)

22
Q

Provide examples of systematic errors.

A

Zero error
Incorrect calibration of an instrument

23
Q

How to check for and eliminate systematic errors?

A
  • check for zero error
  • use another instrument to take the same measurement
  • plot a best fit graph / line
    (Systematic errors can be eliminated only if cause of it is found)
24
Q

Define random error.

A

A random error is one that causes measurements to have varying magnitudes and have an equal chance of being above or below the true value of the measured qty. (random error causes the set of measurements to spread about the true value)

25
Q

Give examples of random errors.

A
  • parallax error (incorrect positioning of eyes while taking a reading on a measuring scale)
  • random human / judgement error (misjudgment of a moving object)
  • random variations in experimental conditions (experimenter’s hand is not steady when holding the instrument)
26
Q

State methods to minimise random error

A
  • take multiple measurements and calculate average
  • Use a more precise instrument
  • plot a best fit graph / line to average out the random error
27
Q

What are the measures of error?

A

Accuracy & Precision

28
Q

Define accuracy

A

Accuracy refers to how closely a measured value agrees with the “true” value. (Affected by systematic errors)

29
Q

How do you judge accuracy of a measurement?

A

The accuracy of a measurement can be judged by comparing the closeness between the mean value and the true value. (Closer = more accurate, vice versa. Refer to notes for more specific diagrams)

30
Q

Define precision.

A

Precision refers to how closely individual measurements agree with each other without reference to any “true” value. (Affected by presence of random errors)

31
Q

How do you judge precision of a measurement?

A

The precision of a measurement can be judged by comparing the amount of spreading. (Less spreading = More precise, vice versa. Refer to notes for more specific diagrams.)

32
Q

Explain absolute uncertainty

A

Absolute uncertainty ΔX is the magnitude of the uncertainty in the measurement of a quantity X.
Absolute uncertainty of X = ΔX (always expressed in 1 s.f.)

33
Q

Explain fractional uncertainty

A

Fractional uncertainty of a qty ΔX can be expressed ass a fractional of the qty X
Fractional uncertainty = ΔX/X

34
Q

Explain percentage uncertainty

A

Percentage uncertainty is the fractional uncertainty multiplied by 100% to express the fraction as a percentage.
Percentage uncertainty = ΔX/X * 100%

35
Q

If Z = kX, where k is a constant, the absolute uncertainty of Z is?

A

ΔZ = k ΔX

36
Q

If Z = nX ± mY, where n and m are constants, the absolute uncertainty of Z is?

A

ΔZ = n ΔX ± m ΔY

37
Q

If Z = kX^nY^m or Z = kX^n/Y^m, where k, n, and m are constants, the fractional uncertainty of Z is?

A

ΔZ/Z = |n| ΔX/X + |m| ΔY/Y

38
Q

If Z = is x, the absolute uncertainty of Z is?

A

ΔZ1 = Zmax - Z and ΔZ2 = Z - Zmin
Where Zmax = sin(X + ΔX) and Zmin = sin(X - Δ X)
Then take ΔZ to be the larger of the two.

39
Q

What is a scalar qty?

A

A scalar qty is one which has magnitude only.

40
Q

What is a vector qty?

A

A vector qty is one which has both magnitude and direction.

9749 H2 Physics (5 decks)

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