LESSON 2Introduction Physics is an experimental science. Theories are useful only if their predictions agree with the results of experiments. So measurement plays an important part in physics.Together with other scientists , physicists have agreed on a single system of units for the measurement of physical quantities . A physical quantity is clearly defined with a numerical value and a unit. A physical quantity can be measured using a standard size called the unit. Units identify the quantity that has been measured. The standard size used must (i) be easily reproduced (ii) not have its magnitude changed (iii) be internationally accepted Although various systems of units have been used over the years, scientists have generally agreed to use the International System of Units (S.I. Unit). Units for the base quantities are known as base units, i.e. metre , kilogram, second, kelvin and ampere. The definition of base units. The metre is the length of the path traveled by light in vacuum during a time interval of 1 of a second 299792458 The kilogram is the mass of a prototype cylinder of platinum-iridium alloy that is kept Units Of Measurement at the International Bereau of Weights and Measures. The second is 9192631770 periods of a specified radiation from Cesium-133 atoms The kelvin is 1 of the 273.16 thermodynamic temperature of the triple point of water The ampere is the current carried by two long parallel wires placed one meter apart, when the attractive force per unit length between two wires is 2 x 10-7 Nm1 . Prefixes Prefix is a scientific notation word before the base units and have certain value uses powers of 10. Prefix Giga Mega Kilo Desi Centi Mili Mikro Nano Symb ol G M k d c m µ n Factor Standard Form The radius of earth 6400000000 mm and the diameter a metal wire is 0.00000045 km. What is the best way to write these numbers ? 5 particularly in the cases of A very small numbers B very large numbers C very small and very large numbers 2 The standard form for 15200 is A C E 3 Example 3 Ekspress 22.152 x 10 -4 Example 2 Convert the following lengths into the units of metre.3 km (b) 0.13 km (e) 345.4 x 10 -2and 5. The shorthand form of writing numbers is called standard form.000078 x 10-6 s (g) 7 x 10-5 x 8 x 106 (h) 3 x 108 + 8 x 106 (i) 6.0045 ms in terms of Ms Solution Example 5 Convert (a) 11.5 cm3 into the units of m3 (b) 72 km j-1 into the units of ms-1 (c) 5 g cm-3 into the units of kgm.3 Solution TUTORIAL 1 Every number can be written in ‘standard form’. (a) 0.2 x 10 3.2 x 10 6 B 1.2 x 10 5 6 .4 is A 1.0068 cm (d) 567.00008 m (b) 5300 g (c) 0.8 x 10-2 -3 .52 x 10 3 0.62 mm (c) 3 x 106 cm Solution The product of 2.2 x 10 2 B 1. Example 1 Write the following numbers in standard form. the standard form number is a x 10n where 1 ≤ a<10 and n are positive integers or negative integers.52 x 10 4 D 1.The best way is try to write the numbers in shorthand form.52 x 10-5 1.0 x 10 .2 x 109 (j) 3.2 x 104 m (f) 0.1 x 103 Solution (a) kg Solution (b) dg Example 4 Ekspress (a) 73 kg in terms of mg (b) 0. (a) 2.5 g in the units of 15. In general.7. 8 Hz 8 13 Which one of the following prefixes is less then 1? A B C Mega Desi Kilo 8 A 5 x 10 seconds is equivalent to 14 Which of the following is true? A B C D 0.2 20 D B 2 0.5 1.056 1.mili.7 x 10 .3 x 10 .7 9 Which one of the following measurements is different? A B C 2.5 x 10 .056 -4 x x x x x 10 Hz 10 6 Hz 10 4 Hz 10 .I.5 x 10 7 g C 1.centi Mikro.4 m cm mm 10 Which one of the following measurements is smallest ? A 1.1 kg 4.7 x 10 .1 3450 = 3. 7 12 The acceleration of a trolley is 2000 cms.2 x 10 .9 = 5.4 kg 11 The measurents of length according to their value in ascending order are A 7 x 10 x 10 4 mm B 7 x 10 x 10 .056 1. 7 x 10 km .7 x 10 –3 B D 3.6789 x 10 3 0.531 =4.2 x 10.5 x 10 .5 1.mili mm . 7 cm .3 x 10 2. The expression of the frequency in units of Hz is A B C D E 1.5 x 10 12 µ g 5 What is 0.056 1.5 3.centi.5 microseconds C 50 microseconds D 500 microseconds E 5000 microseconds E 7 .kilo.450 x 10 4 46.02 7 Radio 5 RTM station operates at 105 .2 kg 45.5 x 10 .C E 4 1.kilo Mega.455 x 10 .6531 x 10 4 5678.giga.giga.55 x 10 .3 x 10 2 4 6 If A = 2 x 10 5 and B = 3 x 10 - then the value of A + 5B is A C E 1.2 x 10 -8 4 D 1.056 1.mega.2 This acceleration ini S.002 0. 7 x 10 mm .05 microseconds B 0. 7 -4 6 The prefixes according to their value in ascending order are A B C D Giga.kilo.4 1.3 x 10 2.3 kg 455 x 10 . 7 x 10 4 2 cm .mikro.5 x 10 2 kg B 1. unit is A C E 0.0455 kg expressed in standard form? A B C D 0.4 km C 7 x 10 x 10 2 cm -4 2 4 km .00023 = 2.4 Hz 10 .3 0.05 = 5 x 10 .6 M Hz.centi Centi. ....... ....6 km The table above shows the measurement of length for four different objects... ................... (e) A cube of sides 7......................... (b) Which reading is the shortest? . .................... ..................... ........................2 x 10 5 µm ..................................................................................2 x 10................. ........................... (a) Which reading is the longest ? .15 Readings 7.............................2 x 10-2 cm 7................2 x 103 mm and 7..... State the volume of the cube in unit of m3 8 ......................... (c) Arrange the readings according descending order..... 7...... (d) Which reading is more than 1 metre? .............2 x 103 mm .