Question

Answer the following question.
With the help of a suitable circuit diagram prove that the reciprocal of the equivalent resistance of a group of resistances joined in parallel is equal to the sum of the reciprocals of the individual resistances. 

Answer 1

Let there are n resistances, each of value RI, R2 Rn, respectively, are connected in parallel to a battery of voltage V. if the equivalent resistance of the circuit is Req, then-current drawn from 
`"i" = "V"/"R"_("eq")`
the battery is 
The total current /then divides into Ii, i2, i3 in, respectively in the given resistors. As all the resistances are connected in parallel, hence the voltage across each resistor is V Volt. Now we can write,
i= i₁ + i₂ + i₃ + ...........+ i_eq

`"V"/"R"_("eq")="V"/"R"_1+"V"/"R"_2+"V"/"R"_3.......+ "V"/"R"_"n"`   ......(1)

From eq. 1, 

`1/"R"_("eq")=1/"R"_1+1/"R"_2+1/"R"_3......+1/"R"_"n"`
Hence, reciprocal of the equivalent resistance is equal to the sum of reciprocal of each resistor joined in parallel