PHYSICS EXAMINATION TECHNIQUES

By Omosa ElijahEmail: omosae@yahoo.com

IMPORTANCE OF PHYSICS• Kenya envisions being

industrialized by year 2020 and vision 2030

• There is need to improve in math, technology and science (physics) for rapid industrialization

IMPORTANCE OF PHYSICS contd.• interest in and performance

in science subjects especially physics is low

• Colleges and employers attach a lot of importance to physics

• Helps one acquire problem-solving and decision-making skills

KNOW YOUR SUBJECT/EXAMINATION• Paper 1: 2 hrs; 80 mks- heat and

mechanics• Paper 2: 2 hrs;80 mks - electricity

and magnetism, waves and modern physics.

• Paper 3: 21/2 hours; 40 marks NB: Paper 3 contributes about 20%

of the total marks. TO SCORE B- < one must score D+ < in P3

HOW TO STUDY PHYSICS (a)READING AND REVISION• Have a well laid down

schedule for revising• Try to have access to the

past papers for examinations• Try discussing questions with

others to test your understanding

(b) BEFORE THE EXAMINATION• Brush through your short notes• Have enough sleep the day before

examination• Pack the materials needed for the

examination before sleeping• Wake up early enough to allow you

reach the examination room 30 minutes to the start of exam

(c) DURING THE EXAMINATION• Write your name and index neatly• Read through the instructions, then all

questions get to understand them• Before answering read and re-read

questions-avoid contradictions!!• Start with the questions that you

understand bestNB: Keep an eye on time-1 min to

one mark!!

(d) IMPORTANT POINTS TO NOTEi) Instructions- read and re-read to make sure that you understand the examiner’s needs. Understand the key words or steps to be followed

ii) Care in reading instruments- when reading instruments be careful with the accuracy, units and in cases where we have multi-scale instruments e.g.. for electricity be sure which one to read!!

(d) IMPORTANT POINTS TO NOTEiii) Data presentation• Record the data as soon as it is made so

as to avoid forgetting • Tabulate data neatly in the format the

examiner wants it.• Be careful of the accuracy of the

instruments used• In the final answer give an answer in the

number of d.p.’s advised or practically obtainable using the instruments used in experiment unless stated.

(d) IMPORTANT POINTS TO NOTEiv) Know how the following instruments work:• Metre rule• Vernier calipers• Micrometer screw gauge• Mass balances• Spring balance• Stopwatch• Thermometer• An ammeter• A voltmeter• A CRO among others

TERMS COMMONLY USED WITH EXAMSa) Compare Give differences and similarities btn A and Bb) ContrastGive differences btn A and Bb) DefineGive a formal statement e.g.. define an ampere c) DescribeState in words or sometimes with aid of diagramsThe main points in a topic or structure or processe.g.. describe a lab. Experiment to determine thefocal length of a convex lens. Normally number ofnecessary steps equal the allocated marks

TERMS COMMONLY USED WITH EXAMSe) State and explain Give a brief description normally of an expected

result and give the hidden science behind it e.g.. state and explain the effect increasing the resistance of a wire on the heat dissipated

f) Discuss To investigate by argument, giving reasons for and

againstg) DistinguishTo discriminate btn A and B by giving differences

e.g.. distinguish between conductors and semiconductors

TERMS COMMONLY USED WITH EXAMSh) Draw a diagram/graph/apparatusMaking simple but neat drawings, but notartistic drawings e.g. draw a graph of y

against x.i) EvaluateJudge worth of something or find thenumerical valuej) ExplainMake clear and intelligible- bring out what

does not seem obvious be understood k) GiveGive/name/list factors or facts

TERMS COMMONLY USED WITH EXAMSl) IdentifyShow that you have recognized an item or a process e.g.. identify the radioactive

radiationm) Predict/infer/deduceApply logic to information or given question,

not memorization to answern) StateGive brief information without supporting

arguments e.g.. statement of laws/principles

TERMS COMMONLY USED WITH EXAMSo) Suggest Means no one answer is treated as correct-it means use of learnt informationin solving a real life situation/problemp) Verify/showTo present in an organized manner so as

to convince, normally by use of equations or experiment that the statement holds true e.g.. show that Archimedes principle leads to the law of floatation.

Typical Example of state & explain• Fig. 2 represents a flaming non-drip candle.

State and explain how the candle’s stability changes as it burns. (2mks)

Stability increases√ centre of gravity lowers √Becomes stable x centre of gravity decreases x

A typical example of exam question: Describe an experiment to determine the focal length of a

converging lens.Solution• Arrange the lens, candle/light source, metre

rule and screen as shown in diagram 1 √ -experiment set-up

u v

candle lens screen

•Adjust the position of the screen so that a sharply focused image √ of the candle is seen on the screen-adjustments done•Measure and record the object distance, u and the image distance, v √.- readings taken/recorded•Repeat the above process √ by adjusting the distance u a few more times each time recording the corresponding values of u and v-repeat of experiment

• Obtain the corresponding values of 1/u and 1/v-processing of results

• Plot a graph of 1/v against 1/u-use made of results. Alternatives to this procedure exist

• The intercepts of 1/u and 1/v on the horizontal and vertical axes respectively give 1/f, where f is the focal length. –prediction of results/physical constant determination

Example of calculation: Determine the pressure due to sea water of density 1030 at a depth of 20 m below the water surface.

SolutionP = hρg√ 1mk- formula = (20)(1030)(10) √ 1mk- substitution = 20600Pa √ 1mk- numerical value

or 20600Nm-2 and correct unit

Way of loosing/gaining marks-calculations

ρ = m √ d = m √ D = m x V V V = 20 √ = 20 √ = 20 √ √ 4 4 4

= 5g/cm3√ = 5g/cm3√ =5g/cm3√

ESSENTIAL MATHEMATICAL SKILLS a) THE ARITHMETIC OF MATHEMATICAL EQUATIONSI) Addition and Subtraction

Make x the subject in y = 2x + 4Solution

y – 4 = 2x + 4 - 4Therefore x = y – 4

2e.g.. v = u – gt, make g the subject

II) Multiplication/Division RuleMake x the subject in 2x = y – 4 Solution2x = y – 4 2 2Therefore x = y – 4 2• e.g.. v = u – gt, make t the subject t = v – u g

ESSENTIAL MATHEMATICAL SKILLS

ESSENTIAL MATHEMATICAL SKILLS III) Cross multiplication Rule P = R or K = l1 Q S L l2

IV) The ‘Do unto others’ RuleEk = Ep

½mv2 = mghv2 = 2gh

therefore v = √2gh

ESSENTIAL MATHEMATICAL SKILLS b) GRAPHS: Hints on Drawing graphsI) Title- short but clear. What to

plot on vertical axis and horizontal axis- it is important to show quantity and unit, unit (not a must)

II) Axes- quantity and unit is a must. Do not interchange the axes

ESSENTIAL MATHEMATICAL SKILLS

V.ADep var. plotted here

V.A Independent variable plotted here H.A

II) Axes-

quantity and unit must be written here quantity and unit must be written here quan

tity

and

unit

mus

t be

writ

ten

here

ESSENTIAL MATHEMATICAL SKILLSIII) Scale • simple and uniform scale – use

steps that are equal and easy to plot and read; avoid numbers like 1 sq. represents 3, 7, 11 e.tc.

• Choose a scale so that the plotted points should also cover btn ½ to ¾ of the graph paper page

ESSENTIAL MATHEMATICAL SKILLSUse a dot with a circle round it or a cross or x place

so that the point/intersection is within one small square. The plot should remain even after drawing

line/curve(a)

ESSENTIAL MATHEMATICAL SKILLS(b)

ESSENTIAL MATHEMATICAL SKILLS

(c)

ESSENTIAL MATHEMATICAL SKILLS(d)

ESSENTIAL MATHEMATICAL SKILLSUse of graphs to obtain physical constants(e)

ESSENTIAL MATHEMATICAL SKILLS(f) Example of straight line graph

ESSENTIAL MATHEMATICAL SKILLS(g) Example of smooth curve (graph)

ESSENTIAL MATHEMATICAL SKILLS(h) Example of non-linear law graph

ESSENTIAL MATHEMATICAL SKILLS(i) Non-linear to linear law conversion :

Using powers

ESSENTIAL MATHEMATICAL SKILLS(i) Non-linear to linear law conversion :

Using logarithms

Graphs Summary

Some important things to remember when drawing graphs.1. Give your graph a title2. Chose a sensible scale for both axes3. Try and draw a graph that will fill the graph paper4. Label the axes5. Put units on both axes6. Plot the points correctly

Graphs Continued 7. Mark the points clearly + or 8. Draw a smooth best fit line through the points. This is often called a trend line. It shows the general trend but you do not have to join up all the points – in fact you should not do this unless they actually fit the trend line.9. Recognise any anomalous points (ones that are way off the general trend).10. Draw the line clearly and finely

Force (Newtons)

Extension (metres)

Other General Considerations• Forces must be drawn as straight

lines with arrows indicating their directions

• Real rays of light must be drawn as straight lines with arrows indicating their directions. The virtual as dotted lines without arrows on them

Other General Considerations contd.

• Numerical values should be accompanied with correct units, otherwise…

• Units named after people should be written not to start with capital letters

• Use constants given by examiner

Other General Considerations contd.• In calculations, do not round off

too early, give answer to the number of decimal places required by the examiner or as the measuring instruments used can practically read

• Transfer of marks exists only from a section to another

Other General Considerations contd.• For micrometer screw gauge and

vernier calipers, show how you read the main/sleeve scale the vernier/thimble then add to get reading!

• Master the graphical methods well• Understand the key words in every

question

END

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