FORM 1-PHYSICS-MEASUREMENT

Concepts of Measurement

Basic Fundamental Quantities

Derived quantities

Basic Apparatus/equipment's and their uses

Basic Apparatus/Equipments Used for Measurement

Describe basic apparatus/equipments used for measurement

Volume

Volume is the amount of space occupied by a substance. The SI unit is cubic meter (mˆ3).Other units used are cubic centimetre (cmˆ3) and litre(l).

Instruments used to measure the volume of liquids:

Measuring cylinder-used for measuring or pouring out various liquids.

Measuring flask and pipette are used for getting fixed pre-determined volume.

Flask

Pipette

Burette-used to deliver any required volume up to its total capacity.

How to read volume measuring instruments(precautions).

Readings are always taken at the level of the bottom of the meniscus or curved surface of the liquid. Mercury is an exception as its meniscus curves downwards.

Care should be taken to place the eye correctly to avoid parallax errors. When taking readings, the pipette and burette must be upright and the cylinder and flask must stand on a horizontal bench otherwise errors may arise from tilting.

Measuring volume of irregular objects.

The volume of an irregular solid can be determined by measuring the volume of water displaced in a measuring cylinder directly or with the aid of an overflow eureka can.

Activity 1

Experiment

Aim: To measure the volume of an irregular object.

Methods

By using a measuring cylinder directly

Materials and apparatus: Irregular object eg; stone, thread, measuring cylinder, eureka can and water.

Procedures

• Poor a known volume of water in a burette(V1)
• Tie a stone with a thread.
• Immerse the tied stone in water holding the thread and record the volume (V2)
• Make sure the stone is totally immersed in water.

Results

• Volume before introducing solid = V1
• Volume after introducing solid = V2
• Volume of irregular solid(V3) = V2 – V1

By using the eureka can

Procedureto follow:

• Poor water into eureka can up to its spout
• Immerse a well tied stone in water completely
• Collect the overflowed water in the water.
• Use a measuring cylinder to determine the volume of water collected

Observation

• When a stone was introduced in an overflow can, water overflowed to the measuring cylinder.
• The volume of water collected is equal to the volume of irregular object(stone)

Sources of Errors in Measurement

Identify sources of errors in measurement

Error is the difference between the measured value and the real or actual value (The difference in reading is known as the error).

There are two types of errors, namely:

1. Systematic errors
2. Random errors

Systematic errors

Systematic errors results in the measurement or reading being consistently over the actual value OR consistently smaller than the actual value.

Sources of systematic errors.

1. Zero error: Zero Error is caused if the reading shown is Not zero when the true value is actually zero. This is most probably caused by a flaw in the instrument for example when using a ruler that has lost its zero scale due to wear and tear hence causing an error in the measurement of length.
2. Wrong assumptions: For example if you assume that water boils at 100 degree Celsius but actually its boiling point is higher if there are impurities in it. (Pure water boils at 100 degree Celsius).
3. Lag of reaction time: For example in a sports day, when measuring a 100 m running time using a stopwatch. The observer may not press the stop button exactly when the foot of the runner touches the finishing line.
4. Calibration errors: Instruments that are not properly calibrated could also cause error and this has to be put in consideration when writing a report or when there is an anomaly in reading.

Random errors.

Random error is caused by the observer who reads the measuring instrument. Just like the systematic error, there is also positive or negative error. Positive error is when the reading is bigger than the real value and negative error is when the reading is smaller than the real value.

Ways of reducing errors

1. Taking several readings and then find the average.
2. Avoiding parallax error by positioning the instrument (meter rule) properly on the table with the eyes perpendicular to the scale.
3. Some instruments can be adjusted to eliminate zero error. For example when using an ammeter, there is an adjuster to set the indicator to zero before making any measurement.
4. In the case of a ruler, measurement can be carried out starting from the next clear scale for example if scale 0.0cm is blurred, we can start measuring the length from 2.0cm, of course taking the difference of value in consideration when recording the final reading.