1.1 measurements and their errors

Question 1

What are SI units?

Answer 1

Fundamental (base) units of physical quantities

Question 2

What physical quantity is measured in mol?

Answer 2

An amount of substance

Question 3

Express 60Tohms in standard form

Answer 3

6x10^13 (T is tera x10^12 )

Question 4

Write 0.000005m as a suitable prefix

Answer 4

5μm μ=10^-6

Question 5

What is the actual value of 8M ohms?

Answer 5

8x10^6 ohms

Question 6

What is 6000pF in nF

Answer 6

6nF as 1 nano = 1000 pico’s

Question 7

What multiplier is associated with the prefix femto

Answer 7

10^-15

Question 8

Express 7G ohms in standard form

Answer 8

7x10^9 ohms

Question 9

What is a random error?

Answer 9

An error that affects precision and cannot be removed , causing changes in measurements

Question 10

What is a systematic error ?

Answer 10

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

Question 11

What are 3 ways to reduce random error?

Answer 11

1) take at least 3 repeats and calculate an average
2) use a computer or data logger
3) Use higher resolution equipment

Question 12

How can systematic errors be reduced ?

Answer 12

By calibrating the equipment before use

e.g: zero the balance when it is empty

Question 13

What is precision?

Answer 13

consistent measurements that fluctuate about a mean value - this does not mean they are accurate

Question 14

What is repeatability ?

Answer 14

The original experimenter can redo the experiment with the same equipment and method and still get the same results

Question 15

What is reproducibility ?

Answer 15

If the experiment is done by somebody different with different equipment and different techniques and still get the same results

Question 16

What is meant by resolution ?

Answer 16

The smallest change in quantity being measured giving a recognisable change in reading

Question 17

What is meant if a value is accurate ?

Answer 17

If the value is close to the true value

Question 18

What is absolute uncertainty ?

Answer 18

Uncertainty given as a fixed value

e.g: 7+/- 0.6V

Question 19

How can percentage and fractional uncertainty be reduced?

Answer 19

Measure larger quantities

Question 20

What is the difference between a reading and a measurement?

Answer 20

Readings are when a value is found a measurement is when the difference between 2 meanings is found

Question 21

What is the uncertainty of a device?

Answer 21

The uncertainty of a reading is +- half the smallest division

Question 22

3 times are given : 3.1 ,3.2 , 3.6 . Find the mean and absolute uncertainty.

Answer 22

Mean: 3.1+3.2+3.6 = 9.9 9.9 /3 = 3.3
Uncertainty = half range 3.6-3.1= 0.5 0.5/2 = 0.25
Answer : 3.3+-0.25

Question 23

What is wrong with writing 7+-0.673V?

Answer 23

Uncertainty should always be given with the same number of significant figures as the answer ie: 7=+-0.7

Question 24

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

Answer 24

91/7=13ms^-2
uncertainty percentage = (0.2/7)100+ (3/91)100= 6.2%
a= 13ms^-2+-6.2%

Question 25

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

Answer 25

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

Question 26

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

Answer 26

Draw the steepest or the shallowest line of worst fit that still goes through the error bars
workout the gradient of the line of worst and best fit and the difference between the 2 is the uncertainty?

Question 27

How do you workout the uncertainty in the y-intercept of the line of best fit ?

Answer 27

best fit y intercept - worst fit y intercept

Question 28

What is an order of magnitude?

Answer 28

Powers of 10 which describe the the size of an object , and which can also be used to compare sizes between objects

Question 29

What is estimation?

Answer 29

A skill physicists must have to approximate the values of physical quantities, in order to make comparisons or to check if answers are reasonable

Question 30

Adding or subtracting uncertainties

Answer 30

adds absolute uncertainty

Question 31

multiplying or dividing uncertainty

Answer 31

add percentage uncertainty

Question 32

raising uncertainty to a power

Answer 32

times percentage uncertainty by power

Question 33

when multiplying to a constant with uncertainties

Answer 33

multiply the uncertainty by constant not the percentage uncertainty