The potential divider is a high resistance connected across supply mains and is used to obtain a variable voltage form a constant voltage supply. TH variable voltage is available across fixed point A and variable point C,

Q. A potential divider of resistance 500 ohms is used to obtain different voltages form 200 volts supply main. Determine the position of the tapping point C to get a current of 2 amperes through a resistance of 30 ohms connected across points B and C.

Solution : Let the resistance of potential divider between points B and C be of R ohm,
The voltage drop in load resistance = 2x30  60V.

The voltage drop across points B and C of potential divider = voltage drop in load resistance 60 V.

Current flowing through the resistance R = 0  amperes
                                                            R
 

             Potential Divider

Since voltage drop across BC = 60 volts
Voltage drop across, AC, V_AC =200-60 = 140 V

Current flowing through portion AC of potential divider, I_AC - 60 + 2
                                                                                    R
Resistance of portion AC of potential divider R_AC = 500-R

Since V_AC = R_AC X I_AC

140 = ( 500-R) ( 60 + 2 )
                        R

or   R = 434.7 Ω

Hence point C lies in such a position that
    
 length BC = 434.7 X 100 = 86.94% of total length        
                   500

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