Page 64 - Electrician - TT (Volume 1)
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ELECTRICIAN - CITS




           Joule’s law can be stated as:  The quantity of heat (H) generated in a conductor of Resistance (R), when a current
           (I) flows through it for a time (t), is directly proportional to:
               The square of current,
               The resistance of the conductor,
               The time at which the current flows
           According to Joule’s Law the heat produced,
               H ∞ I²Rt

           Where
               I is the current,
               R is the resistance
               T is the resistance

           Let V be the potential difference applied between two terminals of a conductor of resistance R,
           Then current I = V/R
           If the current I is passed through a conductor for time t,
           then charge Q = It.
           Potential difference is the work done (w) during flow of charge Q is given by:

           Work = Potential difference X charge
           W = V.Q
           Put V = IR and Q = It
           Then W = I²Rt

           When current flows through a conductor, the work done (I²Rt) is converted into heat.
           Thus Heat produced, H = I²Rt joule (current I is in ampere, resistance in ohm and time in second)
           Usually heat energy expressed in calorie.
           H =  I²Rt  calorie,
                J
           where J is Joule’s constant or mechanical equivalent of heat

           And J = 4.187 calorie
           Hence, heat produced in a conductor in terms of calorie is given by
               I²Rt
                                      V² t
           H =  4187  calorie          H =  RX4187  calorie
                                     Wt
                V  t
                 1
           H =  RX4187  calorie        H =  4187   calorie
           UNIT OF HEAT
           Kilocalorie (kcal) is the unit of heat in MKS system

           It is defined as the amount of heat required to increase the temperature of one kg of water by 10 C.
            4.187 joule    =  1 calorie
            4187 joules   =  1 kilocalorie
            1 joule           =   0.24 calorie

           Temperature
           Temperature is the measure of heat. Thermometer is generally used for measuring temperature. Pyrometer is
           used to measure high temperature




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 CITS : Power - Electrician & Wireman - Lesson 13-19  CITS : Power - Electrician & Wireman - Lesson 13-19
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