ELECTRICAL ENGINEERING

Resistances in Series When some conductors having resistances R 1 , R 2 , and R 3 etc. are joined end on end as in figure below they are said to be connected in series. It can be proved that the equivalent resistance or total resistance between points A and D is equal to the sum of the three individual resistances. Being a series circuit, it should be kept in mind that figure 1 figure 2 (i) current is the same through all three conductors   (I = I 1 = I 2 = I 3 ) (ii) voltage drop across each is different due to Its resistance and is given by Ohm's Law (iii) sum of the three voltage drops is equal to the voltage applied across the three conductors.  There is a progressive fall in potential as we go from point A to D as shown in Figure 3 figure 3   V = V 1 + V 2 + V 3 = IR 1 + IR 2 + IR 3 But V = IR where R is the equivalent resistance of the series combination. IR=IR 1 + IR 2 + IR 3 R eq =R 1 +R 2 +R 3 Resistances in Parallel Three resistances, as joined in Figure 4

 Ohm's Law This law, which is applicable to electrical conduction through reliable conductors, can be formulated as follows. If the conductor's temperature is constant, the ratio of the potential difference (V) between any two places on it to the current (I) flowing between them will remain constant. What I mean is, V/I = constant, or V/I   = R where R is the resistance of the conductor between the two points considered. Put in another way, It simply means that provided R is kept constant, current is directly proportional to the potential difference across the ends of a conductor. However, this linear relationship between V and I does not apply to all non-metallic conductors. For example, for silicon carbide, the relationship is given by V = KI m   where K and m are constants and m is less   Example 1 : A coil of copper has a resistance of 20 ohm at 10 o C   and is connected to a 220 V supply. By how much must the voltage be Increased in order to maintain current c

Not only resistance but specific resistance or resistivity of metallic conductors also increases With rise in temperature and vice versa. According to the picture below the resistivities of metals vary linearly with temperature over a range of temperature, the variation becoming non-linear both at very high and at very low temperatures. Let, for any metallic conductor, ρ 1  =    resistivity at t 1   o C ρ 2  =    resistivity at t 2   o C m  = slope of the linier part of the curve Next, it is evident that m  = (ρ 2  - ρ 1  ) / (t 2  – t 1  )     or      ρ 2  = ρ 1  +  m  (t 2  – t 1  )   or ρ 2  = ρ 1  [1 + ( m/  ρ 1 ) (t 2  – t 1 )   ] The ratio of m / ρ 1 is called the temperature coefficient of resistivity at temperature t 1 0 C. It may be defined as numerically equal to the fractional change in ρ 1 per 0 C change in temperature from t 1 0 C. It is almost equal to temperature-coefficient of resistance α 1 . therefore, substituting  α 1  =  m / ρ 1,  we get  ρ 2  = ρ 1  [1 + α 1  (t

So far we did not make any distinction between values of α ( alpha)   at different temperatures. But it is found that value of  α ( alpha)  itself is not cönstant, but depends on the initial temperature on which the increment in resistance is based. When the increment is based on the resistance measured at 0 0 C, then α has the value of  α 0   ( alpha nol)  any other initial temperature t 0 C, value of α is α t , and so on. It should be remembered that, for any conductor, α 0 has the maximum value.  Suppose a conductor of resistance R 0   at 0 0 C (point A in Fig. above)  is heated to t o C (point B).  Its resistance R t  after heating is given by  R t   = R 0  (1 +  α 0   t)                                                     … eq (1) where   α 0  is the temperature-coeffcient at 0 0 C. Now, suppose that we have a conductor of resistance  R t  at temperature t 0 C. Let this conductor be cooled from t o C to 0 0 . Obviously, now the initial point is B and the final point is A. The fi

Mаn's greatеst dіsсoverу was fіre, a valuable fоrm оf enеrgу, аnd thеn later elеctrісаl energy. Thіs enеrgy haѕ bеen іnѕtrumеntal in dеvеlоріng сivіlizаtions. But, hоw іѕ еleсtrіcity produced? It іѕ рroduced thrоugh thе use оf fuеl sourсеs suсh as water, nuсlear fiѕѕіon, fosѕil fuеlѕ аnd еvеn the wind. In thiѕ аrtiсle we wіll loоk at sоme of thе differеnt mеthоds used in the рrоduсtiоn оf eleсtrical enеrgy. Simply put, the majority of electricity is generated by employing large turbines. These turbines generate power by being pushed, and the following energy sources are used to move the turbines: Foѕsil Fuеls Electricity is created when the enormous turbine blades are moved by substantial amounts of steam. This product is made by boiling water in large furnaces. By burning fossil fuels like petroleum, coal, and natural gas, heat is produced. Unfortunately, cаrbon dіоxіdе is аlѕo рrоduced аs а sіde рrоduct, and thіѕ iѕ rеleаsed intо the аіr рolluting our atmosрhеrе. Thіѕ mаі