2 Nature of quantities Units and measurements

Question 1

What the S.I Base units for mass, length and time

Answer 1

Kilogram, Kg
Metre, m
seconds, s

Question 2

What the S.I Base units for current, temperature and amount of substance

Answer 2

ampere, A
kelvin, K
mole, mol

Question 3

Define Homogenity of units

Answer 3

Units in an equation must always be the same on both sides

Question 4

Mulitple of unit for pico

Answer 4

p 1×10^-12

Question 5

Mulitple of unit for nano

Answer 5

n 1×10^-9

Question 6

Mulitple of unit for micro

Answer 6

µ 1×10^-6

Question 7

Mulitple of unit for milli

Answer 7

m 1×10^-3

Question 8

Mulitple of unit for centi

Answer 8

c 1×10^-2

Question 9

Mulitple of unit for deci

Answer 9

d 1×10^-1

Question 10

Mulitple of unit for Kilo

Answer 10

K 1×10^3

Question 11

Mulitple of unit for mega

Answer 11

M 1×10^6

Question 12

Mulitple of unit for giga

Answer 12

G 1×10^9

Question 13

Mulitple of unit for tera

Answer 13

T 1×10^12

Question 14

Accuracy

Answer 14

Accuracy-How close the mean value of your measurement is to the true value

Question 15

Human error

Answer 15

Mistake made by a person, results in an anomolous result

Question 16

Systematic error

Answer 16

caused by mistake in calibration of the measuring equippment. affects accuracy not precision

Question 17

zero error

Answer 17

type of systematic error where the equipment gives a reading when it should read zero

Question 18

random error

Answer 18

casued by fluctuations in the object you are measuring or the equipment. can affect accuracy and precision

Question 19

How do you add or subtract data with uncertainties?

Q. A wire is stretched from 0.3 ±0.1 cm to 0.5 ±0.1 cm. Calculate the extension of the wire

Answer 19

Add the absolute uncertainties

A. 0.5 - 0.3=0.2
0.1 + 0.1 =0.2
so Extension in wire is 0.2 ±0.2 cm

Question 20

How do you multiply or divide data with uncertainties?

Q. A force of 15 N ±3% is applied to a stationary object which has a mass of 6.0 ±0.3 Kg.
Calculate the the acceleration of the object and state the % uncertainty in this value

Answer 20

Add the percentage uncertainties

A. a=f/m
    15/6=2.5ms^-2
    %uncertainty in mass=(0.3/6)×100=5%
Total uncertainty= 3% + 5%
so acceleration = 2.5ms^-2 ±8%

Question 21

How do you find %uncertainty for data with powers?

Q. The radius of a circle is r=40cm ±2.5%. What will the %uncertainty be in the area of this circle (πr^2)

Answer 21

Multiply the %uncertainty by the power

A. 2.5% × 2=5%

Question 22

For single readings what is the absolute uncertainty?

Answer 22

The actual uncertainty and is the same as the resolution of the measuring instrument

Question 23

For single readings what’s the percentage uncertainty?

Answer 23

(absolute uncertainty/measured value) ×100

Question 24

For multiple readings what’s the absolute uncertainty?

Answer 24

(largest value-smallest value)/2

Question 25

For multiple readings whats the precentage uncertainty?

Answer 25

(absolute uncertainty/mean) ×100

Question 26

What’s an error bar?

Answer 26

Shows the absolute uncertainty of individual points on a graph. It ca be plotted in x and y direction

Question 27

How do you calculate %uncertainties of final results from a line of best fit?

Answer 27

1. Add error bars to each point (usually the same)
2. Draw line of best fit, max line and min line (worst lines)
   3.Calculate: uncertainty= (grad of best fit - grad of worst fit)
   Or (max grad - min grad)/2
3. %Uncertainty=(uncertainty/grad of best fit) ×100

Question 28

Precision

Answer 28

Precision-How close together repeat values are

Question 29

How do you work out %uncertainties in the intercept from the max and min gradients?

Answer 29

1. draw line of best fit and extrapolate it to find the ‘best value of the y intercept”
2. Draw max and min grads and extrapolate them to get max and min value for the y intercept
3. Determine the diffrence between the max and min values then halve it to find the uncertainty in the y intercept
4. %uncertainty= (uncertainty/best y intercept value) x 100

Question 30

What is the resolution of a measuring equipment

Answer 30

The smallest change it can read

Question 31

callibrated

Answer 31

an accurate scale has been established by comparison to a known standard