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# PHY301_LEC01

International System of Units:

. It is built upon seven basic units.
. These are meter, kilogram, second, ampere, Kelvin, mole and candela.

Basic Units :

The seven quantities are known to be basic in SI unit System.

Meter :

Up until 1983, the meter was defined as 1,650,763.73 wavelengths in a vacuum of the orange-red line of the spectrum of krypton-86. Since then, it is equal to the distance traveled by  light in vacuum in 1/299,792,45 of a second.

Second :

The second is defined as the duration of 9,192,631,770 cycles of the radiation associated with a specified transition of the Cesium-133 atom .

Kilogram :

1. The standard for the kilogram is a cylinder of platinum-iridium alloy kept by International Bureau of Weights and Measures at Paris.
2. The kilogram is the only base unit still defined by a physical object.

Kelvin (1) :

1. The Kelvin is defined as  the fraction 1/273.16 of the thermodynamic temperature of the triple point of water, that is, the point at which water forms an interface of the solid, liquid and vapor
2. This is defined as .01oC on the Centigrade scale and 32.02oF on Fahrenheit scale.
3. The temperature 0oK is called the “absolute zero”.

Ampere :

The Ampere is defined as that current, if maintained in each of two long parallel wires separated by a distance of one meter, would produce a force, between the two wires, of 2 x 10-7 newtons, for each meter of length .

Candela :

The Candela is defined as the luminous intensity of 1/600,000 of a square meter of a cavity at a temperature of freezing platinum (2,042 ok).

Mole :

The mole is defined as the amount of substance of a system that contains as many elementary entities as there are as many atoms in 0.012 kilogram of the Carbon-12.

Joule :

1. Joule is defined as the energy consumed in moving an object of one kg through a distance of one meter
2. One joule is equivalent to the 0.7376 foot pound-force and .2388 calories.

watt :

1. Watt is defined as the “Rate of doing work.”
2. One watt =1 joule/second
3. One watt is equivalent to 0.7376 ft–lbf/s or equivalently 1/745.7 horsepower

Decimal System :

1. The SI system uses the decimal system to relate larger and smaller units to basic units.
2. It employs prefixes to signify the various power of 10.

Decimal System (Prefixes) :

Example 1 :

A laser emits light at a wavelength of 248nm. This is same as
(a) .0248 millimeter.
or
(b) 2.48 micrometer.
or
(c) 0.248 micrometer.
or
(d)24800 angstrom.

``````The answer is
(C) 0.248 micrometer``````

Example 2 :

A logic gate switches from the on state to the off state in 10 neno seconds, this corresponds to
(a)0.1 micro second
or
(b)10 micro second
or
(c) .001 micro second
or
(d) .01 micro second

``````The answer is
(d) .01  micro second``````

Sub-atomic elements :

1. Electron : It is a negatively charged particle
2. Proton: It is a positively charged particle
3. Neutron: It is a neutral particle and carries no charge

Electrons and protons in an Atom :

1. An atom is the smallest particle of the basic elements which form the physical substance we know as solid, liquid and gas.
2. Each stable combination of electrons and protons make one particular type of atom.
3. To understand the concepts of electronics we must have the understanding what is happening at the atomic level, not why it happens.
4. There are number of methods by which electrons and protons might be grouped.
5. They assemble in specific atomic combination for a stable arrangement.
6. As a result, the electron stays in its orbit around the nucleus.
7. In an atom that have more electrons and protons than hydrogen atom, all the protons are in nucleus, while all the electrons are in one or more rings around the nucleus.