Question

A circuit is to be designed to keep the voltage across a 50Ω resistor constant when the supply voltage changes. Two resistors of resistances 100 Ω and 50 Ω are connected in series across a 110 V AC source. Determine the voltage across the 50 Ω resistor. If the supply voltage varies between 100 V and 120 V, what is the required range of variations in the 100 Ω resistor required to keep the voltage across the 50 Ω resistor constant? 

Answer 1

According to ohm's law

$V=IR$

For a constant $I$

$V\alpha$ $R$

voltage across $50\varOmega$ resistor

= $\frac {50}{150}×110$

=36.67$V$

When the supply voltage is 100$V$ voltage across 100$\varOmega$

=$100-36.67$

=$63.33 V$

When the supply voltage is $120V$

Voltage across $100\varOmega$

=$120-36.67$

=$83.33$

Therefore the range is

$63.33V$ to $83.33V$