Base quantity 1
A physical quantity is .. 2
Examples of scientific instruments stopwatch, metre rule, triple beam balance, thermometer, ammeter, voltmeter, spring balance, etc. 3
A base quantity is a physical quantity which cannot be defined to other physical quantities. 5
List of 5 basic physical quantities and their units.
i) Light intensity unit candela
ii) Amount of substance unit mol Derived quantities 1
A derived quantity is a physical quantity which combines several basic quantities through multiplication, division or both. 2
Determine the derived unit for the following derived quantities. t EMBED Equation.3 ForceFforce mass x acceleration F makg m s-2Newton (N)pressureP EMBED Equation.3 , P F/AN m-2Pascal (Pa)weightWweight mass x gravitational acceleration W mgkg m s-2Newton (N)workWwork force x displacement W FsN mJoule (J)powerP EMBED Equation.3 , P W/t , P E/tJ s-1Watt (W)kinetic energyEk EMBED Equation.3 Ek mv2kg m2 s-2Joule (J)potential energyEpP.E mass x gravitational acceleration x height 2.
It will be written before the unit as a multiplying factor. 3.
The list of prefixes 4.
Some physical quantities have extremely large magnitudes. These extremely large and small values can be written in standard form or using standard prefixes. Write the quantities in standard prefixes a.
Frequency of radio wave 91 000 000 Hz 9.1 x 10 1MHz
Diameter of the earth 12 800 000 m 12.8 Mm 1.28 x 10 1 Mm
Distance between the moon and the earth 383 000 000 m 383 Mm 3.83 x 10 2 Mm
Mass of the earth 6 000 000 000 000 000 000 000 000 kg 6.0 x 10 12 Tm Standard Form 1
Standard form A x 10n, 1 A 10 and n integer 2
Standard form is used to simplify the expression of very large or small numbers 3
Some physical quantities have extremely small magnitudes. Write them in standard form Radius of the earth 6 370 000 m 6.37 x 106 m Mass of an electron 0.000 000 000 000 000 000 000 000 016 73 kg 1.673 x 10-27 kg c.
Size of a particle 0.000 03 m 3.0 x 10-4 m b.
Diameter of an atom 0.000 000 072 m 7.2 x 10-8 m c. Wavelength of light 0.000 000 55 m 5.5 x 10-7 m SCALAR AND VECTOR QUANTITIES 1
Scalar quantities are quantity which has only magnitude only
Examples Mass, Length, Speed, volume, distance 2
Vector quantities are quantity which has magnitude and direction
Examples Velocity, Force, Displacement, Acceleration 2
We must know how to choose the appropriate instrument to measure a particular quantity 3
Examples of instrument and its measuring ability. Measuring instrumentRange of measurementSmallest scale divisionMeasuring tapeUp to a few meters1 cmMeter rule1 m0.1 cmVernier caliper13 cm0.01 cmMicrometer screw gauge2.5 cm (25 mm)0.01 mm (0.001 cm)4
Sample of measuring instruments 4.1
Ammeter is use to measure electric current Measuring cylinder is use to determine the volume of liquid Ruler is use to determine the length
Vernier calliper is used to measure a.
small object b.
depth of a hole
external diameter of a cylinder or pipe d.
internal diameter of a pipe or tube
A vernier calliper gives readings to an accuracy of 0.01 cm.
Length of vernier scale 0.9 cm
Vernier scale is divided into 10 divisions
Length of the divisions 0.09 cm The diagram below shows a vernier calliper with reading.
Vernier calliper reading 0.15 cm 4.5
Micrometer screw gauge. A micrometer screw gauge is used to measure a.
objects that are small in size b.
diameter of a wire
diameter of small spheres such as ball bearings
Function of ratchet to prevent from exerting too much pressure on the object. 4.6 Some others measuring instruments
Hands-on activity 1.1 on page 1 of the practical book to learn more about choosing appropriate instruments....
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