Скачать с ютуб Current Electricity Class 12 Physics - Cell and EMF and Internal Resistance в хорошем качестве

Current Electricity Class 12 Physics - Cell and EMF and Internal Resistance

Current Electricity Class 12 Physics - Cell and EMF and Internal Resistance A cell consists of two electrodes, positive electrode denoted by P and negative electrode denoted by ‘N’. these are immersed in solution called electrolyte. Positive electrode exchange charges from electrolyte and develop positive potential V+, similarly, negative electrode generates negative potential (V- ); where V+ is greater than 0 and V- is less than 0 respectively. In absence of current, the potential difference between P and N. is, V+-(-V-) = V++V-. This difference is called electromotive force (EMF) of cell, denoted by ε. where, ε = V++V- greater than 0. Significance of EMF: Suppose in given circuit steady current is maintained using a cell. Current flows from positive to negative terminal outside the cell and negative to positive terminal within the electrolyte of the cell. Electrolyte through which current flows has finite resistance r, called as internal resistance. If R is infinite, I =V/R = 0; Where V is potential difference between electrodes P and N. therefore V= potential difference between P and A + potential difference between A and B + potential difference between B and N = ε. hence, emf ε is potential difference between the positive and negative electrode in absence of current. If R is finite, I is not zero. Hence, potential difference between P and N is V= V+ + V- - Ir V = ε - Ir ; negative sign of Ir is due to flow of current from B to A. Also by Ohm’s law, V=IR Hence, IR= ε - Ir IR+Ir = ε I(R+r) = ε I = ε / (R+r) Therefore, maximum current flows through the circuit when resistance R=0 and Imax= ε/r.