Measurements and Errors

Question 1

What is accuracy?

Answer 1

How close the results are to the true value.

Question 2

What is precision?

Answer 2

How close each data point is together (variance).

Question 3

What is error?

Answer 3

The uncertainty due to the measuring instrument (difference between measured and expected value).

Question 4

What is random error?

Answer 4

Refers to random fluctuations in the measured data.

Question 5

State three factors which could cause a random error.

Answer 5

The readability of the instrument, the effects of something changing in the surroundings between measurements and the observer making a mistake.

Question 6

What is a systematic error?

Answer 6

Refers to reproducible fluctuations consistently in the same direction.

Question 7

State three factors which could cause a systematic error.

Answer 7

An instrument being wrongly calibrated, An instrument with a zero error and the observer making the same mistake in every reading.

Question 8

How do you correct for a zero error?

Answer 8

The value when it should be zero should be subtracted from every reading.

Question 9

How can you reduce random error.

Answer 9

Take repeat measurements (at least three).

Question 10

How can you reduce systematic error?

Answer 10

Calibrate the measuring instrument by measuring a known value. e.g. measure a 1kg mass on scales.

Question 11

How should water level in a tube be measured?

Answer 11

From the lowest point and in the middle of the meniscus (the dip in the water).

Question 12

What is parallax error?

Answer 12

Taking an incorrect reading from the measuring instrument due to taking the reading from an angle other than directly in-line.

Question 13

What is uncertainty stated as?

Answer 13

Plus or minus the least count (smallest value).

Question 14

What is the uncertainty on a ruler?

Answer 14

Plus or minus 0.1cm

Question 15

What is the uncertainty of a stopwatch?

Answer 15

Plus or minus 0.3s due to taking human reaction times into account. (This must be clearly stated if done)

Question 16

What is the difference between a reading and a measurement?

Answer 16

A reading where the zero is assumed to be correct such as with a thermometer but a measurement is where the zero is manually placed such as with a ruler.

Question 17

What is the uncertainty for readings?

Answer 17

Plus or minus half the smallest value.

Question 18

What is the uncertainty for measurements?

Answer 18

Plus or minus the smallest value.

Question 19

How would you state the resistance of a lamp given some data points?

Answer 19

The resistance of the lamp is the mean plus or minus half the range. Anomalous data points aren’t included in finding the mean or range.

Question 20

How do you work out percentage uncertainty?

Answer 20

((Approximate value - Exact value) / Exact value) x 100 or (Absolute uncertainty / recorded value) x 100

Question 21

What should be done if an equation is used which introduces new terms which weren’t mentioned in the question?

Answer 21

Define the terms of the equation.

Question 22

What is a vernier calliper?

Answer 22

A measuring instrument capable of more precise readings.

Question 23

What do more precise readings from a vernier scale do?

Answer 23

Reduce systematic error.

Question 24

What type of error is a parallax error?

Answer 24

Random error.

Question 25

How can you reduce the uncertainty of a measurement of the width of a constantan wire?

Answer 25

Measure the width in an odd number amount of places randomly along the wire and calculate an average.

Question 26

What is the resolution of a voltmeter?

Answer 26

0.01V

Question 27

What is the resolution of an ammeter?

Answer 27

0.01A

Question 28

What is the resolution of a micrometer?

Answer 28

0.01mm

Question 29

What is the resolution of a 30cm ruler?

Answer 29

1mm

Question 30

How can the heating effect be reduced when measuring the resistivity of a wire?

Answer 30

Take the length measurements from longest to shortest and switch off the current between readings.

Question 31

How do you deal with errors worked out from equations with powers?

Answer 31

Multiply the error by the power.

Question 32

State four safety considerations for the resistivity in the constantan wire experiment.

Answer 32

Don’t touch the wire when it is hot or there is current flowing, switch off the power if you smell burning, switch off the power between readings and wear safety goggles.

Question 33

What is the value of the prefix: Pico?

Answer 33

x10^-12