Practical Skills COPY

Question 1

When is there a parallax error?

Answer 1

When your reading is wrong because your eye is not at the same level as the point you are measuring

Question 2

How can you avoid parallax error?

Answer 2

By using a set square to correctly line your eye up or by using a mirror

Question 3

How do you use a mirror to reduce parallax error?

Answer 3

Place your scale behind the pin you are trying to measure, place your mirror next to the scale and behind the pin, move your eye until the pin hides its own reflection.

Question 4

What can you use callipers to measure?

Answer 4

Measurements of distances up to 20 cm

Question 5

When you use a micrometer for measurements?

Answer 5

When the distance is below 3cm

Question 6

Why are micrometers better than callipers?

Answer 6

They have a better resolution

Question 7

How do you use a micrometer correctly?

Answer 7

Check its 0 reading and note the 0 error if there is one, Take a reading and note the measurement after allowing if necessary for the 0 error

Question 8

What type of error is a 0 error?

Answer 8

A systematic error

Question 9

What kind or error is a variation in diameter?

Answer 9

A random error

Question 10

When should you do repeat readings?

Answer 10

When measuring something such as diameter of a wire or the thickness of a slide

Question 11

Why is it good to repeat readings?

Answer 11

It reduces the percentage error

Question 12

What is the error in a stopwatch?

Answer 12

+/- 0.01

Question 13

Why is there some error when using stopwatches? What kind or error is this?

Answer 13

Random errors caused by starting and stopping too early or too late due to human reaction times / difficulty judging

Question 14

What is the error in a range of readings?

Answer 14

Half the range

Question 15

What is the uncertainty if half of the range of the readings < 0.01?

Answer 15

It is the precision of the instrument measuring

Question 16

Why should you do multiple oscillations instead of one when timing oscillations?

Answer 16

Reduces the percentage error

Question 17

Where should a fiducial marker be placed when measuring oscillations?

Answer 17

At the centre of the oscillation as this is where the speed is greatest

Question 18

What do fiducial markers reduce when timing oscillations?

Answer 18

Absolute errors

Question 19

What must you always say when a balance is used?

Answer 19

State that you zero the balance the pressing the tare button

Question 20

What is a random error?

Answer 20

An error which may be too big or too small by different amounts each time a reading is repeated

Question 21

What will reduce random errors?

Answer 21

By taking repeated readings and then taking a mean

Question 22

What is a systematic error?

Answer 22

An error which is always too big or too small, often by the same amount.

Question 23

Where do systematic errors usually come from?

Answer 23

The measuring instruments

Question 24

Where can systematic errors come from?

Answer 24

A fault with the instrument (zero error) ; there is an additional factor that has not been accounted for (friction)

Question 25

How do you lessen 0 errors?

Answer 25

Check for a 0 error and then either adjust the instrument, or take account of this error in your measurements

Question 26

What is the error in most measurements?

Answer 26

Half what you can read it to

Question 27

What is the error when measuring length?

Answer 27

What you can read it to

Question 28

What are some other reasons errors can occur when measuring lengths, other than the error in the ruler

Answer 28

it is hard to make the thing being measured straight against the ruler

Question 29

How do you calculate percentage uncertainty?

Answer 29

uncertainty / value (or mean value) x100

Question 30

Why should you try to make measurements as large as possible?

Answer 30

To reduce the percentage error

Question 31

How do you combine uncertainties when two values are being added or subtracted?

Answer 31

Add the uncertainties

Question 32

How do you find the most accurate measurement when asked to compare?

Answer 32

Calculate the percentage uncertainty and find the measurement with the lowest

Question 33

How do you find the error in a reading when two separate readings, each with their own errors are multiplied or divided?

Answer 33

Add the percentage uncertainty then convert to absolute uncertainty

Question 34

How do you find the error in a measurement when it is squared?

Answer 34

Multiply the percentage uncertainty by the power then convert to absolute uncertainty

Question 35

How do you reduce uncertainties?

Answer 35

(1) Using higher resolution apparatus (2) Calibrate the equipment (3) Increase the size of the measurement

Question 36

How do you calculate percentage difference between the measured value and the theoretical value?

Answer 36

(theoretical - measured) / theoretical x100

Question 37

How do you find the percentage uncertainty in a gradient?

Answer 37

|(best gradient - worst gradient)| / best gradient x100

Question 38

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

Answer 38

|(Best y-intercept - worst y intercept)| / best y intercept x100

Question 39

What could the 'worst gradient' be?

Answer 39

The steepest gradient possible or the shallowest gradient possible

Question 40

How do you check direct proportion using a table of results

Answer 40

Divide the corresponding sets of values and if the value is constant then the variables are directly proportional

Question 41

How do you check if a values is approximately constant?

Answer 41

Divide max by min and is the value is < 1.10 then the values are approximately constant

Question 42

How do you check inverse proportion from a table of results?

Answer 42

Multiply the sets of values of the two variables. If they are constant they are inversely proportional

Question 43

How do you check if decay is exponential?

Answer 43

Look at the variables at regular time intervals t0, t2, t3, t4. if t1/t0 = t2/t1 = t3/t2 then the decay is exponential

Question 44

What should log or ln values be given to?

Answer 44

3 d.p.

Question 45

What are the advantages of data logging over traditional methods?

Answer 45

(1) can take two measurements simultaneously (2) eliminates reaction time error that comes from stop clocks (3) can measure changes in a very short time period (4) can measure changes in a long space of time which is good because you don't have to be there (5) Can be automatically put on a spreadsheet (6) Sample rate can be much greater

Question 46

Define accuracy

Answer 46

A measurement result is considered accurate if it is judged to be close to the true value that would be obtained by an ideal measurement

Question 47

Define calibration

Answer 47

Markig a scale on a measuring instrument. this involves establishing the relationship between indications of a measuring instrument and a standard or reference quantity values, which must be applied.

Question 48

Define measurement error

Answer 48

The difference between a measured value and the true value

Question 49

Define anomalies

Answer 49

Values in a set of results which are judged not to be part of the variation caused by random error

Question 50

Define a fair test

Answer 50

Only the independent variable has been allowed to affect the dependent variable

Question 51

Define hypothesis

Answer 51

A proposal intended to explain certain facts or observations

Question 52

Define interval

Answer 52

The quantity between readings eg a set of 11 readings over a distance of 1 m would give an interval of 10 cm

Question 53

Define precision

Answer 53

Precise measurements are ones in which there is very little spread about the mean value. Precision depends on the extent of random errors - it gives no indication of how close the results are to the true value.

Question 54

define prediction

Answer 54

A statement suggesting that will happen in the future, based on observation experience or hypothesis

Question 55

Define range

Answer 55

The minimum and maximum values or the independent variables

Question 56

Define repeatable

Answer 56

A measurement is repeatable if the original experimenter repeats the experiment using the same method and equipment and obtains the same results

Question 57

Define reproducible

Answer 57

A measurement is reproducible if the investigation is repeated by another person, or by using different equipment or techniques, and the same results are obtained

Question 58

Define resolution

Answer 58

The smallest change in the quantity being measured of a measuring instrument that gives the perceptible change in the reading

Question 59

Define uncertainty

Answer 59

The interval within which the true value can be expected to lie, with a given level of confidence or probability

Question 60

Define validity

Answer 60

Suitability of an experiment procedure to answer the question being asked

Question 61

Define continuous variable

Answer 61

Have values that can be given magnitude either by counting or by measurement

Question 62

Define control variables

Answer 62

One which may, in addition to the independent variable, affect the outcome of the investigation and therefore has to be kept constant or monitored

Question 63

Define dependent variable

Answer 63

The variable which the value is measured for each and every change in the independent variable

Question 64

Define independent variable

Answer 64

The variable for which values are changed or selected by the investigator.