Practical Skills

Question 1

What is resolution of a measuring device?

Answer 1

This is the smallest change on a measuring instrument that gives a perceptible change in the reading.

Question 2

In experiments what is precision?

Answer 2

A measure of the spread of the values about a mean value
(high presiscion = small spread)

Random errors determine precision of data

Question 3

How is precision different to accuracy?

Answer 3

Precision is how close the values are to a mean value

Accuracy is how close that mean value is to the actual value

Results can be precise but inaccurate (eg with a systematic error)

Question 4

What makes a measurement accurate?

Answer 4

If it is close to the true value (within its absolute uncertainty)

Question 5

What is a measurement error?

Answer 5

Taking a reading and that is different to the actual value
(caused by random or systematic errors)

Question 6

What are the 2 types of measurement errors?

Answer 6

**1. Random
2. Systematic **
Subcategories: zero, callibration, parallax, reaction time

Question 7

What is an anomaly?

Answer 7

An incorrect measurement outside of the range of uncertainty

Question 8

How do you deal with anomalies in results?

Answer 8

• Repeat measurement if possible
• If not discount anomalous result

Question 9

What is a random error?

Answer 9

Something unpredictable that causes results to be randomly spread out around a true value

Question 10

How do you reduce random errors in experiments?

Answer 10

Take repeat measurements and calculate averages

Question 11

What is a systematic error?

Answer 11

An error that causes all results to be affected by the same amount (eg reaction time using stopwatch)

Can be caused by miscalibrated equipment (zero error)

Question 12

How do you reduce systematic errors in experiments?

Answer 12

Ensure equipment is correctly calibrated or alter the method

Question 13

What is a parallax error?

Answer 13

An error caused by viewing the object and the scale at an angle rather than square on.

Question 14

What 2 things do you do to reduce parallax errors in experiments?

Answer 14

1. Bring eyeline as level with scale as possible with a mirror
2. Place measuring equipment as close to object as possible
3. Use a set square to align the object and the scale

Question 15

What type of error is this?

Answer 15

Random error (Reduced by taking repeats and average)

Question 16

What type of error is this?

Answer 16

Parallax

Question 17

What type of error is this?

Answer 17

Systematic

Question 18

What kind of error is this?

Answer 18

Systematic

Question 19

What makes an experiment a fair test?

Answer 19

Only one variable is changed (independent variable) to affect the dependent variable

Question 20

For a scientific result to be accepted what 2 conditions must the experiment meet?

Answer 20

1. Repeatable - If you can perform the experiment again and get the same result
2. Reproducible - If someone else can perform the same experiment and get the same result

Question 21

In experimental science what is absolute uncertainty?

Answer 21

The interval which the actual value of a measurement is expected to lie in

Question 22

How is absolute uncertainty for a measurement determined?

Answer 22

• = resolution of equipment x number of judgements made
  or
• Half range of repeats (discount anomalies)
  or
• reasonable estimate based on other factors e.g. kinked wire or reaction time

Question 23

What is the absolute uncertainty here?

Answer 23

±1𝑚𝑚
(measurement = 2 x resolution)

Question 24

What is the absolute uncertainty here?

Answer 24

±0.01V
(reading = resolution)

Question 25

What is the **absolute uncertainty** in these measurements?

Answer 25

±0.05s (0.045 but rounded to match s.f. of the answer)

Question 26

What is the reading on this **venier scale**?

Answer 26

10.02cm

Question 27

What is the reading on this **venier scale**?

Answer 27

3.34cm

Question 28

What is the reading on this **micrometer scale**?

Answer 28

10.83mm

Question 29

What is the reading on this **micrometer scale**?

Answer 29

2.88mm

Question 30

How do you calculate **percentage uncertainty**?

Answer 30

absolute uncertainty/value x 100

Question 31

How do you **combine uncertainties** for measurements that are multiplied or divided?

Answer 31

**Add together their percentage uncertanties** Do not add together their absolute uncertainties

Question 32

How do you **combine uncertainties** for measurements that are added or subtracted?

Answer 32

**Add together their absolute uncertanties** Do not need to add together their percentage uncertainties

Question 33

What has been done wrong here?

Answer 33

Cannot add together absolute uncertainties if units are different Must **only add together percentage uncertainties**

Question 34

What has been done wrong here?

Answer 34

Anomalous result shouldn't have been included AND the absolute uncertainty should be half the range

Question 35

What do **error bars** show?

Answer 35

**Graphically shows absolute uncertainty in one** of the **measurements** (x or y axis)

Question 36

What do **error boxes** show?

Answer 36

**Graphically shows absolute uncertainty in both** of the **measurements** (x and y axis)

Question 37

What is the **absolute uncertainty** in this reading?

Answer 37

Question 38

How do **error bars** help with analysing results?

Answer 38

1. Visually show precision of experiment 2. Help identify anomalous results 3. Allow more precise gradient line to be drawn

Question 39

How do you work out the **percentage uncertainty of a gradient**?

Answer 39

(gradient of best fit - gradient of worst fit line)/(gradient best fit) x 100 OR (Half the range between the steepest and shallowest line)/mean x 100

Question 40

How do you work out the **percentage uncertainty of a y-intercept**?

Answer 40

(intercept of best fit - intercept of worst fit line)/(intercept best fit) x 100 OR (Half the range between the steepest and shallowest intercept)/mean x 100

Question 41

How do you combine these **uncertainties**?

Answer 41

1. Add together percentage uncertainties 2. **Multiply power by corresponding percentage uncertainty**

Question 42

How do you combine these **uncertainties**?

Answer 42

1. Add together percentage uncertainties 2. **Multiply power by corresponding percentage uncertainty**

Question 43

Which of these experiments is more successful?

Answer 43

g2. As the actual value is within it's absolute uncertainty

Question 44

What is wrong here?

Answer 44

Absolute uncertainties must match decimal points of measurements

Question 45

What is wrong here?

Answer 45

Calculated values should match the s.f. of the source values

Question 46

What is wrong here?

Answer 46

Units should be put in the column headings

Question 47

What is wrong here?

Answer 47

Values in each column for recorded data should have the same number of decimal places (they were measured by the same instrument)

Question 48

What is wrong here?

Answer 48

Scale should go up in 1s, 2s or 5s

Question 49

What is wrong here?

Answer 49

Axis need titles and units

Question 50

What is wrong here?

Answer 50

Data take up less than half of the page Instead ** use a broken axis if possible**

Question 51

What is wrong here?

Answer 51

**Data points should always be plotted with crosses** (not dots)

Question 52

What is wrong here?

Answer 52

**Don't force Line of Best Fit through origin**

Question 53

What is wrong here?

Answer 53

**Gradient triangle should be as large as possible**

Question 54

How do you **reduce the percentage uncertainty** of a measurement?

Answer 54

1. Use measuring device with smaller resolution 2. Take bigger measurements if possible (eg use bigger distances in experiment)

Question 55

In this SHM experiment why is time measured over 10 oscillations?

Answer 55

Reduces absolute uncertainty of each oscillation by 10x

Question 56

In this double slit experiment why is distance measured between 11 dots?

Answer 56

Reduces absolute uncertainty of each distance by 10x

Question 57

How is **absolute uncertainty** for a **reading** determined?

Answer 57

* =Resolution of equipment * =Half range of repeats (ignoring anomalies)

Question 58

What is the difference between a **reading** and a **measurement**?

Answer 58

**Reading** - 1 judgement **Measurement** - 2 judgements to calculate value (usually for distances and angles) Absolute uncertainties for measurements = 2 x uncertainties for readings

Question 59

How do you calculate the **absolute uncertainty in a y-intercept?**

Answer 59

intercept of best fit - intercept of worst fit line OR Half the range between the steepest and shallowest intercept

Question 60

How do you calculate the **absolute uncertainty in a gradient?**

Answer 60

gradient of best fit - gradient of worst fit line OR Half the range between the steepest and shallowest line

Question 61

What is **Empirical Evidence?**

Answer 61

Evidence that is **based on observation** and not on theory or a derivation (eg the 3 gas laws were created using empirical evidence)