GCE O-Level Physics

Electrostatics Notes

2009-01-22T18:17:00.000-08:00

Current electricity

2009-01-21T21:27:00.000-08:00

Cambridge Phy 2007 Report

2009-01-20T18:45:00.000-08:00

Phy Forumula list

2009-01-20T18:30:00.000-08:00

Physics Definition List

2009-01-20T18:26:00.000-08:00

Physics SPA Skill 3 PLANNING OUTLINE

2009-01-20T16:55:00.001-08:00

Physics SPA Skill 3 PLANNING OUTLINE

1.) Producing a logical plan

a) Defining the problem

Involves identifying two measurable quantities that are related to each other and suggesting a clear statement of the task to be undertaken.

Example 1: How does the temperature of a squash ball affect its bounce?
The bounce of the squash could be associated with the height of rebound of the ball(measurable quantity)

A suitable statement of task can be: The two Measurable quantities,

Example 2:

You are to design an experiment to see if elastic bands are suitable to be used as a simple spring balance,

This task would be more clearly defined if we investigate how the extension of the elastic band is changed by the weight attached to it. If there is a direct proportionality between extension and weight, we can calibrate the elastic band to measure forces. hence, a simple spring balance.

A suitable statement of task can be
To investigate the relationship how much the elastic band is affected by the number of weights,

b) Identify Independent and Dependant variables

Example: The number of weights is the independent variable (x-axis)
The extension of the elastic band is the dependent variable. (y-axis)

c) Identifying Constant Variables

In practice, there are many independent variables that will affect a chosen dependent variable. To obtain a reliable insight into the relationship between two physical quantities, it is very important to identify these independent variables constant throughout the experiment.

Constant Variables	How to keep these variables constant
......... of ball	Use the same ball throughout the experiment
......... of material	Use the same ball throughout the experiment
.......... of impact	Ensure ball falls vertically
...... at which ball is released	Ensure ball is released at the same height for all readings.

d) Choose Appropriate Procedures

Draw a labelled diagram of the experimental set-up
List the apparatus needed of the investigation. Where appropriate, give a brief description of the features of the apparatus and its mode of operation.
The experimental procedure should be step-by-step, logical and clear. It should be capable of meeting the goals expressed in the statement of task.
A table of results with proper headings/units should be presented.
Plot a graph to display the relationship between the dependent variable (plotted on y-axis) and the independent variable (plotted on x-axis)
Several statements of precaution should be written. It should be able to answer two important questions, namely

WHAT YOU HAVE DONE?
WHY DID YOU DO IT?

Precautions can fall into two categories:

i) Precautions to ensure safety of experimenter and those around him/her.
For example:

Place a heavy weight on the retort stand to prevent it from toppling and hitting someone.
ii) Precautions to ensure reliability of results.
For example:

Stir hot water continuously in order to obtain uniformity of temperature.

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2.) Evaluating procedures and modifying plans

a) Evaluate the Plan and procedures

Discuss the degree to which your experiment could yield results that are reliable and accurate. Consider the following questions:

is there a need to simply procedures so that measurements can be reproduced with by another person?

Are the measuring instruments chosen appropriate?

Does the experiment produce results with a constant trend?

Are repeated measurements close to each other or differ widely?

How much scattering are there in the plotted graph?

Are the constants obtained from gradient and intercepts consistent with known accepted values?

b) Modifications and Improvements

eg1: Visual estimation of the rebound height could be replaced by the use of data loggers(such as motion sensor)

Increase the range of readings (eg. 50.0-90.0 cm to 20.0-90.0 cm)

Increase the number of readings within a certain range. This is necessary if your graph is a curve and more values are required around the turning point.

Modifying techniques in order to make the experiment as precise and reproducible as possible.

Modify techniques to avoid sources of error

Modify techniques to reduce random error.

GCE O Level Physics Common Misconceptions

2009-01-18T19:13:00.001-08:00

Physics Misconceptions:

SCREENSHOTS:

DOWNLOAD:

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

Electrictiy- Potential Divider

2008-12-31T06:48:00.000-08:00

principles of thermometry

2008-12-31T00:10:00.000-08:00

What is temperature ?

A measure of the degree of hotness of a body.
is measured using a thermometer

The choice of thermometer depends on
range of temperatures to be measured
accuracy required
physical conditions of the matter concerned

What must all thermometers have?

A physical property that changes with temperature.

Examples of thermometric properties can be……..

expansion of a column of liquid in a capillary tube
the electrical resistance of a platinum wire
the voltage of a thermocouple
the expansion of a bimetallic strip
the pressure of a gas at constant volume

What makes an ideal thermometer ?
an easy-to-read scale
safe to use
sensitive to temperature changes
ability to measure a wide range of temperatures

What does calibrating a thermometer mean?

Putting a standard scale on a thermometer,
To do this, two fixed points to be marked are first chosen.
for the purpose of standardisation
always the same under given conditions

How to get the Celsius scale?

The two fixed points for the celsius scale are:

Ice Point	Steam Point
Temperature of pure melting ice at standard atmospheric pressure	Temperature at which boiling water changes into steam at standard atmospheric pressure
Assigned value of 0°C	Assigned value of 100°C

Next, the interval between the fixed points is divided into 100 equal divisions for easy reading.
Each reading is 1 degree Celsius (°C)

the Celsius scale

Note height of mercury in the tube at the ice point and the steam point
For any height x of the mercury, the corresponding Celsius temperature  is given by

the Kelvin or absolute scale

The Kelvin scale has its zero at absolute zero
This is the lowest temperature that any substance can reach.

has a SI unit of kelvin (K)
absolute zero corresponds with –273°C on the Celsius scale

T (kelvin) =  (celsius) + 273

thermocouples

consists of two wires of different metals joined together at the end to form two junctions
if the junctions are at different temperatures, a voltage is produced

the larger the temperature difference, the larger the voltage produced
suitable for measuring wide temperature differences, which vary rapidly due to its quick response and the temperature at a point as the wire junctions are very small

the temperature range depend on the two metals used for the wires
can operate over a very wide range of temperatures from –200°C to 1700°C

to produce a larger voltage, several thermocouples are connected in series (thermopiles) to increase the sensitiviy of the instrument