Errors in Measurements

Parallax Errors

-a parallax errors is an error in reading an instrument because the observer's eye and pointer are not in line perpendicular to the plane of the scale
-to avoid parallax error?
*the position of the eye must be in the line with the readings to be taken
*to overcome parallax errors in instruments with the scale and pointer,often have a mirror behind the pointer.The correct reading is obtained by making sure that the eye is exactly in front of the pointer,so that the reflection of the ponter in the mirror is behind it.

CONSISTENCY,ACCURACY AND SENSITIVITY

http://www.mediafire.com/?wser2iyjnem

Errors in Measurement

• mo measurement is exact.All measurements will have some degree of error or uncertainty
• there are two main types of errors : -systematic errors ,-random errors

Systematic Errrors

-systematic errors are cumulative errors that can be compensated for,if the errors are known

-systematic errors in measurement result from

* an incorrect position of the zero point

*an incorrect calibration

-a zero error arises when the measuring instrument does not start from exactly zero

-zero errors are consistently present in every reading of a measurement so that the results obtained may be precise but lack in accuracy

-systematic errors explain why all readings taken are always larger or always smaller than the true value

-systematic errors cannot be elaminated by repeating the measurements and averaging out the results.It only can be elaminated or corrected if the measuring instruments are calibrated or adjusted frequently.

Random Errors

-random errors arise from unknown and unpredictable variations in condition,and will produce a different error every time you repeat the experiment.They may vary from observation to observation.

-random errors are caused by factors that are beyond the control of the observers.

-random errors may occur for a variety of reasons.They may be due to

*personal error such as human limitations if sight and touch

*lack of sensitivity.When there is an insignificant or small change,an instrument may not be able to respond to it or to indicate it or the observer may not be able to discern it

*natural errors such as changes in wind,temperature,humidity,refraction,magnetic field or gravity while the experiment is in progress.

*the use of a wrong technique of measurement such as applying excessive pressure when turning a screw gauge

-random errors can be minimised by reapiting the measurements several times and taking the average or mean value of the readings

Study Tips
Preparing for Physics Exams

Preparing for an exam in physics has two parts. You must make sure that you know how to work problems given a list of formulae, and you must ensure that you can reproduce the formulae. These tasks are rather separate.
The first step in ensuring that you can work problems is to keep up with the assignments as they are due. There is simply too much to learn to postpone this work to the last minute. As you go along you should make sure that you have mastered each type of problem. You should review assigned problems that you got wrong and get help with those where you do not understand what you did wrong. You should know how to work all the assigned problems correctly soon after the marked problems are returned.
In preparing for the exam you should go back over the assignments and make sure you still understand them. Then work a few other problems from the book with the book closed (you won't have the text to browse through on the exam). It is OK to verify the details of a formula, but not to look for what the appropriate formula is.
At the same time you should be organizing your mastery of the formulae. Outlines are the best way to do this since the formulae form a logical pattern. It is best to organize the outline so that you can use it for "guess/check" learning. To do this make an outline of labels of formulae (Acceleration due to a given force, Energy conservation, etc.) and place the formulae themselves on the right-hand side of the page where they may be covered up. Then repeatedly go down the outline attempting to reproduce the formulae and working on those you cannot write down. Eventually you will know them all, usually faster than you will using any other method. Remember that most formulae need not be memorized: use units, qualitative arguments, linearity, and the like to aid your reconstruction of the formulae. The less you have to memorize, the more confidence you will have in the testing room.
Looking at old exams will help you to get used to your instructor's testing style. This will aid you in deciding which areas are important and what kind of skills your instructor wants you to learn. However, be cautious. No one exam can cover everything that an instructor considers important, so don't ignore a topic you think is important simply because it fails to appear on old exams.
Another good use of old exams is in testing your preparation when you think your study is finished. For this purpose work the problems on earlier exams without using your text or notes. If you can do this easily, you are probably well prepared.
During the exam read all the questions and answer the ones you know best first. If you have time, check all the problems at the end of the testing period. It is easiest to do this if you have plugged in numbers last. If you run out of time, outline quickly what you would like to do; many instructors give substantial partial credit for this. The instructor expects you to explain how you got your answer, not just what the answer is. You should therefore put on the paper relevant diagrams, all algebraic steps, etc.
With proper preparation, you should have enough confidence in what you know to tell yourself that "if I can't work this problem, no one else can either." If you are this well prepared, a difficult test should not cause you to panic.

Scalar Quantities

~ a scalar quantity is a physical quantity which has magnitude ir size only
~ a scalar quantity is completely described once its magnitude is known
~ Example : distance,speed,volume,temperature and time


Derived Quantity

~ a vector quantity is a physical quantity which has direction and magnitude
~ a vector quantity is completely described only if both its magnitude and direction are stated
~example : velocity,density,work,acceleration,force

Velocity

do visit this link:
http://library.thinkquest.org/10796/ch2/ch2.htm#Sec3

Base Quantities and Derived Quantities

Base Quantities and Derived Quantities

A base quantity is a physical quantity that cannot be derived from other physical quantities.
Example : -length (m)
-mass (kg)
-time (s)
-temperature (Kelvin)
-electric current (Ampere)

A derived quantity is a physical quantity that can be calculated or expressed in terms of base quantity.
Example : - area
-volume
-density
-velocity
-acceleration
-work
-power

Understanding Physics

Understanding Physics

Physics is traditionally defined as the study of matter and energy and the relationship between them.
Physics is the science that describe how the physical world works.

Work

Work
Definition: The work done by an agent exerting a constant force ( ) and causing a displacement ( ) equals the magnitude of the displacement, s, times the component of along the direction of . In Figure 5.1, the work done by is:

W = s Fcos .



Figure 5.1: Work



Note:

If = 0 W = 0. (ie: no work is done when holding a heavy box, or pushing against a wall).
W = 0 if (ie: no work is done by carrying a bucket of water horizontally).
The sign of W depends on the direction of relative to : W > 0 when component of along is in the same direction as , and W < 0 when it is in the opposite direction. This sign is given automatically if we write as the angle between and and write W = Fscos .
If acts along the direction of then W = Fs , since cos = cos 0 = 1.
Work is a scalar.
The SI units of work are Joules (J) (1 Joule = 1 Newton meter). In cgs units: 1 erg = 1 dyne cm.

Power

Power
Definition: Power is the time rate of doing work or, the amount of work done per second.

Average Power:


= = F = F (9)

where t is the time interval in which the work is done.

Instantaneous Power:


P = Fv.

Note:

Power is a scalar.
SI Units: 1 Watt ( W ) = 1 Joule/sec = 1 kg m 2/ s 3
British Engineering Units: 1 horsepower ( hp ) = 746 W .

Kinetic Energy and the Work Energy Theorem

Kinetic Energy and the Work Energy Theorem
Idea: Force is a vector, work and energy are scalars. Thus, it is often easier to solve problems using energy considerations instead of using Newton's laws (i.e. it is easier to work with scalars than vectors).

Definition: The kinetic energy ( KE ) of an object of mass m that is moving with velocity v is:


KE = mv 2. (1)

Note:
Kinetic energy is a scalar.
The units are the same as for work (i.e. Joules, J).
Relation bewteen KE and W: The work done on an object by a net force equals the change in kinetic energy of the object:



W = KEf - KEi. (2)

This relationship is called the work-energy theorem.
Proof (for parallel to ):


1.
W = Fs W = (ma)s (by Newton's second law).
2.
From the third equation of motion: as = (v 2 - v02)/2 W = 1/2m(v 2 - v02) = KEf - KEi .
Note:

If the speed of an object increases ( vf > vi ) W > 0.
If W < 0 then the object is doing work on the agent exerting the net force.
Interpretation of Eq.(5.2): We can think of KE as the work an object can do in coming to rest.

Potential Energy Stored in a Spring

Potential Energy Stored in a Spring
Definition: The spring constant, k , is a measure of the stiffness of a spring (large k stiff spring, small k soft spring).

To compress a spring by a distance x we must apply a force F ext = kx . By Newton's 3rd law, if we hold a spring in a compressed position, the spring exerts a force Fs = - kx . This is called a linear restoring force because the force is always in the opposite direction from the displacement.


Note:

The sign of Fs shows that the spring resists attempts to compress or stretch it; therefore Fs is a restoring force.
For Example: In Figure (5.2a) x = xf - xi = - 5 which gives Fs = - k(- 5) = 5k . This force is positive and therefore directed to the right. This means that the spring resists the compression. In Figure (5.2b) x = xf - xi = 3 which gives Fs = - 3k . The negative sign indicates that the force is to the left and that the spring resists the stretching.



Figure: a) Compressed spring b) Stretched spring



The farther we compress or stretch the spring, the greater the restoring force.
We usually define xi = 0 and xf = x which gives Fs = - kx . This is called Hooke's law.
To find the potential energy stored in a compressed (or stretched) spring, we calculate the work to compress (or stretch) the spring: the force to compress a spring varies from F ext = F0 = 0 (at xi = 0 ), to F ext = Fx = kx (at xf = x ). Since force increases linearly with x , the average force that must be applied is


= (F0 + Fx) = kx

The work done by is W = x = kx 2. This work is stored in the spring as potential energy:

PEs = kx 2. (4)

Note:
PEs = 0 when x = 0 (at equilibrium).
PEs always > 0 when the spring is not in equilibrium.
PEs is the same if x = xf (same PEs for equal expansion or compression).

Gravitational Potential Energy

Gravitational Potential Energy
Definition: Gravitational Potential Energy ( PEg ) is given by:

PEg = mgy, (3)

where m is the mass of an object, g is the acceleration due to gravity, and y is the distance the object is above some reference level.
The term ``energy'' is motivated by the fact that potential energy and kinetic energy are different aspects of the same thing (mechanical energy).

For Example: When an object is dropped from rest at some height above the earth's surface, it starts with some PEg but no KE. As the object falls towards the Earth, it loses PEg and gains KE. Just before the object hits the ground, it has lost all of its initial PEg but gained an equal amount of KE.

Proof: Find the work done by the force of gravity when an object falls from rest at position yi to yf = 0 . We have W = Fs , F = |m| = mg and s = (yi - yf) = yi . This gives, W = mgyi .

Combining with Eq.(5.2) gives 1/2m(vf2 - 0) = mgyi or PEi = KEf .

TIPS TO SCORE PHYSICS

Tips to score physics

1. Grap the definition for physics terminology
-specific heat capacity
-latent heat
- refraction
-pressure
-micro wave
-work done
-resultant force
-resolution of force
-forces of equilibrium
-focal length
-len's power
-magnetic field
-half life
-beta ray
-gamma ray
-interference
-logic gate
-momentum
-impulsive force
-GM tube

2. Grap the physics principle and their applications

*principle of conservation of momentum
*principle of conservation of energy
*principle of force in equilibrium
*principle of thermal equilibriu
*Pascal's principle
*Bernoulli's principle
*Archimedes principle
*Superposition principle

3. Grap the physics law and applications
:Hooke's Law
:Boyle's Law
:Charles' Law
:Pressure Law
:Snell's LAw
:Ohm's Law
: Lenz's Law
:Newton 1st Law of motion
:Newton 2nd Law of motion
:Newton 3rd Law of motion
:Law of reflection
:Law of refraction
:Faraday's Law

4. Grap the physics rule
#Right hand grip rule
#Maxcell cork screw rule
#Fleming's left hand rule
#Fleming's right hand rule

5. Grap the physics formula

6. Grap the physics examination format
~Score P1(50Marks)
~Score P2(37Marks)
~Score P3(40Marks)
~Examination mark scheme

7.Grap the method of answeringquestion
=P1 - Do the easier question first
=P2 - Observation skill,point form,table form,ranking method
=P3 - Get the variables,tabulation of data,draw the graph

8. Grap the method of answering quatitave application question
*Write all the information again. use symbols
*Choose the formula
*Make subtitution
*Final answer with correct unit

9. Grap all the physics experiment

10. Grap the physics content using
-Mind map
-Check list

11. Grap the past years SPM exam papers
# Year 2004
# Year 2005
# Year 2006
# Year 2007

12. Grap the drawing skill
- ray diagram of lenses
- ray diagram of plane and curve mirror
- diagram of instruments
- diagram of experiments

13. Grap the working principle of instruments
-hydrometer
-manometer
-barometer
-bunsen burner
-carburretor
-electric motor
-electric generator
-astronomical telescope
-compund microscope
-nuclear reactor
-fibre optic
-electric bell
-electric relay
-laud speaker
-hydraulic brake
-submarine
-pariscope
-binocular
-microphone
-Cathode Ray Oscilloscope (CRO)
-semiconductor diode
-transistor

14. Grap the graph skill
-drawing
-sketcing
-interpretation
-determining the gradient

15. Grap the unit conversion skill
~ normal conversion
~ conversion involving derived quantities
~ conversion involving area
~ conversion involving volume

16. Grap calculation skill
~ use the calculator
~ use basic algebra
~ use the basic trigonometry
~ use the basic proportional method

17. Grap the question's skill analysis
- sketch/draw diagram
- underline the important words
- write all the information again using symbols
- think for the topics,sub topics,principle,law,theory,rule and total marks

WORK,ENERGY AND POWER

http://tutor4physics.com/workenergy.htm

FORCES AND MOTION

http://www.glenbrook.k12.il.us/gbssci/phys/Class/newtlaws/u2l1a.html

kAmi aNak-aNak fiZik mengUcaPkan seLamAt bErcUti uNtuK sEmuA pElAjAr 4 al-FarAbi 2008

wElc0mE to tHe wOrLd oF pHy5cis......