Question

Question 44:
An electric bulb is rated as 10 W, 220 V. How many of these bulbs can be connected in parallel across the two wires of 220 V supply line if the maximum current which can be drawn is 5 A ?

Lakhmir Singh Physics Class 10

Answer 1

Answer:Aãl fùzäß

Explanation:

Answer 2

Answer:

110 bulbs

Explanation:

Given,

Voltage rating of bulb = 220 V

Power rating of bulb = 10 W

$\textrm{Since,\ power\ rating\ is\ given\ by,\ W}\ =\dfrac{V^2}{r}\\\\\textrm{So,\ the\ resistance\ is\ give\ by\ r,}\ =\ \dfrac{V^2}{W}\ =\ \dfrac{220\times 220}{10}\ \Omega=\ 4840\ \Omega$

Since, the total current is taken by th ecircuit is,I = 5 A and as in the parallel circuit voltage is same in each branch. So,equivalent  $\textrm{resistance}, R =\dfrac{V}{I}\\\\\ =\ \dfrac{220}{5}\ = 44\ \Omega$

In parallel connection of resistance the equivalent resistance is given by,

$\dfrac{1}{R}\ =\ \dfrac{1}{R1}+\dfrac{1}{R2}+\dfrac{1}{R3}+\dfrac{1}{R4}$....

but here we have to connect resistance of same value, r so,

$\ \dfrac{1}{R}\ =\ \dfrac{1}{r}+\dfrac{1}{r}+\dfrac{1}{r}+\dfrac{1}{r}$...upto n times

$\ \dfrac{1}{R}\ =\ \dfrac{n}{r}\\\\=>\ \dfrac{1}{44}\ =\ \dfrac{n}{4840}\\\\\ =>\ n\ = 110$

Hence, the total number of bulbs can be connected is 110.