Checklist-General Physics1. Physical quantities and unitsLearning outcomesCandidates should be able to:(a) show an understanding that all physical quantities consist of a numerical magnitude and a unit

(b) recall the following SI base quantities and their units: mass (kg), length (m), time (s), current (A), temperature (K), amount of substance (mol)

(c) express derived units as products or quotients of the SI base units and use the named units listed in this syllabus as appropriate

(d) use SI base units to check the homogeneity of physical equations

(e) show an understanding of and use the conventions for labelling graph axes and table columns as set out in the ASE publication Signs, Symbols and Systematics (The ASE Companion to 16–19 Science, 2000)

(f) use the following prefixes and their symbols to indicate decimal submultiplesor multiples of both base and derived units: pico (p), nano (n), micro (μ), milli (m), centi (c), deci (d), kilo (k), mega

(M), giga (G), tera (T)

(g) make reasonable estimates of physical quantities included within the syllabus

(j) distinguish between scalar and vector quantities and give examples of each

(k) add and subtract coplanar vectors

(l) represent a vector as two perpendicular components.

2. Measurement techniques

Content2.1 Measurements2.2 Errors and uncertaintiesLearning outcomesCandidates should be able to:

(a) use techniques for the measurement of length, volume, angle, mass, time, temperature and electrical quantities appropriate to the ranges of magnitude implied by the relevant parts of the syllabus.

In particular, candidates should be able to:• measure lengths using a ruler, vernier scale and micrometer• measure weight and hence mass using spring and lever balances• measure an angle using a protractor• measure time intervals using clocks, stopwatches and the calibrated time-base of a cathode-ray oscilloscope (c.r.o.)• measure temperature using a thermometer as a sensor• use ammeters and voltmeters with appropriate scales• use a galvanometer in null methods• use a cathode-ray oscilloscope (c.r.o.)• use a calibrated Hall probe(b) use both analogue scales and digital displays(c) use calibration curves(d) show an understanding of the distinction between systematic errors (including zero errors) and random errors(e) show an understanding of the distinction between precision and accuracy(f) assess the uncertainty in a derived quantity by simple addition of actual, fractional or percentage uncertainties (a rigorous statistical

treatment is not required).

Measuring Length’s:Lengths are measured using • Rulers• Measuring Tapes• Micrometers • Vernier Calipers(You are acquainted with the first two but not

with the last two- )

Micrometer

A Micrometer

Note: We will work with Millimeter Micrometer

Micrometers

Vernier Caliper

Vernier Caliper

8

Calculations:

i)Read what value corresponds to the main scale’s 0: 8.5ii)Read the value on the vernier scale that corresponds with the main scale: 5iii) Pick value ii)- divide it by the number of divisions-> 5/10=0.5mmiv)Notice that the units of the main scale and the vernier scale are different:v) 0.5mm-> cm= 0.5/10=0.05Final Value: 8.5+ 0.05=8.55

0.1

1

9

0.1 cm division on main scale and 1 mm division on the vernier scale.

A bit on the Zero Error:

Positive : Subtract zero error value from the final value;Thimbles 0 is below the main scale line

Positive : Add zero error value to the final value;Thimbles 0 is below the main scale line

0 0-(4*0.01)=0.04mm0+(2*0.01)=0.02mm

Zero Error on Vernier Calipers

Is this Positive Zero Error or Negative Zero Error?What is the Zero Error.It is positive zero error.

Why measurement?

• Measurements are inevitable in order to make careful and accurate observations in Physics.

The Difference between Readings & Measurement; Uncertainty &Error.

• A reading is a single determination of the value of an unknown quantity. It is the actual reading taken during an experiment.

• A measurement on the contrary, is the final result of the analysis of a series of readings. A measurement is only accurate up to a certain degree depending on the instrument used and the physical constraints of the observer. Any quantity measured has an amount of uncertainty or error in the value obtained.

The relation btw Uncertainty and Instrument.

• Explanation; in any instrument reading an integer value wrong is highly implausible, but on the contrary, reading out a decimal value is mostly the reason for errors and that’s why the number of decimal digits becomes the absolute error of the instrument!

Example

• A micrometer measure’s up to the accuracy of one tenth of a millimeter. The value on it’s sleeve is 3mm.

State the value of it’s:• Uncertainty.• Absolute Error• Fractional Error• Percentage Error

2. Measurement techniquesContent2.1 Measurements2.2 Errors and uncertaintiesLearning outcomes

Candidates should be able to:

(a) use techniques for the measurement of length, volume, angle, mass, time, temperature and electrical quantities appropriate to the ranges of magnitude implied by the relevant parts of the syllabus.

In particular, candidates should be able to:• measure lengths using a ruler, vernier scale and micrometer• measure weight and hence mass using spring and lever balances• measure an angle using a protractor• measure time intervals using clocks, stopwatches and the calibrated time-base of a cathode-ray oscilloscope (c.r.o.)• measure temperature using a thermometer as a sensor• use ammeters and voltmeters with appropriate scales• use a galvanometer in null methods• use a cathode-ray oscilloscope (c.r.o.)• use a calibrated Hall probe(b) use both analogue scales and digital displays(c) use calibration curves(d) show an understanding of the distinction between systematic errors (including zero errors) and random errors(e) show an understanding of the distinction between precision and accuracy(f) assess the uncertainty in a derived quantity by simple addition of actual, fractional or percentage uncertainties (a rigorous statistical

treatment is not required).

For those who had problems regarding least count/absolute error

• 36.7= decimal places: 1 hence, 1/10=0.1• 3.62= decimal places: 2 hence, 1/100=0.01• 3.633= decimal places: 3 hence, 1/1000=0.001• Etc.

Hence we deduce that the least count is the smallest value that can be measured by an instrument and to find it out by a value/number,

• DeductionCount the digits after the decimal; if n digits,1/10^n number of digits is equal to the least count.

• Notice that you can only use this when you have the least count as tenth, hundredth, thousandth or the likes.

• What if you have the least count as 0.5, or 0.05, or 0.007?

Therefore; summing it up:

• Hence we deduce that if least counts are not specified, it is then that we use the least count deduction that we discussed, otherwise they will always be specified.

Anomalies in Questions relating to uncertainties:

Sometimes Past Paper Questions have Uncertainties as:

• Uncertainty=Value+- (50% least count)• Uncertainty=Value+- (least count)• Also sometimes it’s • Uncertainty=Value +-(value given in question

irrespective of the instrument/Remember odd least counts?)

Words and Meanings

Systematic:Random:

• Three basic parts make up the brain;• Cerebrum,• Brainstem• Cerebellum.

Certain mechanisms within the Cerebrum are responsible for the registration, storage and retrieval of information. The Cerebrum is divided by fissures into lobes. The outer layer of the Cerebrum is known as the Cerebral Cortex, this is approximately 1cm deep, and it is here that information is received and sent on for storage.

• A structure in the cerebral cortex contains the Hippocampus which acts as a control centre in that it decides what needs to be stored and what is necessary for recollection.

• In short, I want you all to store this piece of information in you brain.

What then?

• See Errors are of two types:

• Systematic Errors • Random Errors

• According to the definition: the former should have the same set of values.

• The latter should have fluctuating values.

• So every time you measure a systematic error, your value either increases or decreases.

• Actual Value=20,• Reading 1: Value=20+6=26• Reading 2: Value=23+6=29• Reading 3: Value=10+6=16

• Error remains constant and hence final value either increases or decreases.

• Hence your value is reacting in a regular order

• Reading 1: Value=20+6=26• Reading 2: Value=22-7=15• Reading 3: Value=20-10=10

• Size of error changes either increases or decreases.

• So value either increases or decreases.

• Lets look into Pacific Physics to get a grip of the concept.

Random Errors

• Some Question!

• Practice all the questions from Pacific Physics.