Physics and Measurement

Transcription

1 Chapter:- 1. Physics and Measurement 1- Length: The Standard International unit of length is the meter. The length of the meter was defined as the distance between two lines on a specific platinum iridium bar stored under controlled conditions in France. ١ 1 millimeter (mm) = 10-3 meter 1 micrometer (µm) = 10-6 meter 1 Nanometer (nm) = 10-9 meter

2 2 Mass The basic SI unit of mass, the kilogram (kg), is defined as the mass of a specific platinum iridium alloy cylinder kept at the International Bureau of Weights and Measures at Sèvres, France. 1 kg = 10 3 g Figure 1. The National Standard Kilogram No. 20, an accurate copy of the International Standard Kilogram kept at Sèvres, France, is housed under a double bell jar in a vault at the National Institute of Standards and Technology (NIST). ٢

3 3 - Time The basic SI unit of time is second (s) 1 ms = 10-3 s 1 µs = 10-6 s 1 Ns = 10-9 s Figure 2. The primary frequency standard (an atomic clock) at the NIST. This device keeps time with an accuracy of about 3 millionths of a second per year. (Courtesy of National Institute of Standards and Technology, U.S. Department of Commerce ٣

4 DENSITY It is defined as mass per unit volume. (الرص اص) For example, aluminum has a density of 2.7 g/cm 3, and lead has a density of 11.3 g/cm 3. The difference in density between aluminum and lead is due to their different atomic masses. m ρ = V The atomic mass ( ال ذري (ال وزن of an element is the average mass of one atom. One mole of substance A contains the same number of atoms as 1 mol of another substance B. 1 mol of aluminum contains the same number of atoms as 1 mol of lead, known as Avogadro s number, NA = 6.02 x 1023 atom/mol ٤

5 The mass of a solid cube is 856 g, and each edge has a length of 5.35 cm. Determine the density ρ of the cube in basic SI units. ٥

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7 Example A rectangular plate has a length of (21.3 ± 0.2) cm and a width of (9.80 ± 0.1) cm. Find the area of the plate and the uncertainty in the calculated area. (9.80 ± 0.1) Solution Area = l w = (21.3 ± 0.2 cm) x (9.80 ± 0.1 cm) = (21.3 x 9.80 ± 21.3 x 0.1 ± 0.2 x 9.80) cm 2 (209 ± 4) cm 2 (21.3 ± 0.2) cm Problem : A solid piece of lead ( الرص اص م ن ص لبة (قطعة has a mass of g and a volume of 2.10 cm 3. From these data, calculate the density of lead in SI units (kg/m 3 ). ٧

8 Units and Dimensions of physical quantities: physical quantities physical equation Dimensional Units formula Length Fundamental [L] m Mass Fundamental [M] Kg Time Fundamental [T] S Temperature Fundamental [θ] K (Kelvin) Electric Current Fundamental [I] A (Ampere) Luminous Intinsty Fundamental [C] Cd (candle) Amount of Substance Fundamental [N] mol (mole) Area (A) A=l*d [L 2 ] m 2 Volum (V) V=A*h [L 3 ] m 3 Velocity (v) =distance/time [LT -1 ] ms -1 Acceleration a = velocity/time [LT -2 ] ms -1 Force F=m*a [MLT -2 ] Kg m S -2 Work or Energy W=F*d [ML 2 T -2 ] Kg m 2 S -2 Volume denisty = mass/volume [ML -3 ] Kg m -3 Momentum M m =mass*velocity [MLT -1 ] Kg m S -1 Charge Q= i*t [I T] A. S=Coulomb Pressure or Stress Pr =Force/Area [ML -1 T -2 ] Kg m -1 S -2 Power P = F*v [ML 2 T -3 ] Kg m 2 S -3 =Watt Strain St = l / l dimensionless unit less Angle Θ =length/radius dimensionless unit less Frequency f = vibration /time [T -1 ] Cycles/S=Hz ٨

9 Also: 1 inch = 2.54 cm 1 feet = cm 1 mile =1.6 km 1 pound-mass = 454 gm 1 liter =1000 cm 3 EQUATION DIMENSION Writing Units Derivation Correction of the of the physical relation of the physical relation physical relation Example: (1) Check the correctness of the following relations: ν = ν ο x + at Dimensions of L.H.S =V = [LT -1 ] """""' R.H.S = [LT -1 L] + [LT -2 T] = [L 2 T -1 ] + [LT -1 ].: Dimensions of L.H.S Dimensions of R.H.S The gavin relation is incorrect. ٩

10 SIGNIFICANT FIGURES When physical quantities are measured, the measured values depends on : The quality of the apparatus آفاءة الجهاز مهارة الفني The skill of the experimenter عدد مرات القياس The number of measurements performed ١٠

11 Q :the distance between two lines on a specific platinum iridium bar stored under controlled conditions in France. A) Millimeter B) Meter C) kilogram D) Second Q : The basic SI unit of time. A) Millimeter B) Meter C) kilogram D) Second Q.3 The density of matter equal: A) ρ = v/m B) ρ = v*m C) ρ = m/v D) no ans. Corrects Q.4 The equation dimension using: A) Writing Units of the physical relation B) Derivation the physical relation C) Correction the physical relation D) All of these Q.5 What dimensions of these physical quantities: Velocity(v), Force(F), Acceleration (a)?, A) LT -3, LT, M -1 LT -1 B) LT -1, LT -2, MLT -2 C) MLT -1, LIT -2, ALT -2 D) CT -1, LMT -2, LT -2 Q.6 When physical quantities are measured, the measured values depends on: A) Quality of the apparatus B) Skill of the experimenter C) Number of measurements performed D) All of these ١١