Question

Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. How many lamps can be connected in series with each other across the two wires of 220 V line if the maximum current allowed is 5 A?​

Answer 1

Answer:

Given, V = 220 V

Power rating of each bulb, P = 10 W

Total current, I, = 5 A

Let number of lamps in parallel be n

Let individual resistance of each lamp be R

From Joule's law of heatin8

P = V?/R

10 220 /R

...)

R= 48400

....(i)

= Ra = R

Ri = R2 .

For resistances in parallel,

1

1

1

1

Req R R2 R

...(il)

From (i) and (iii),

.. v)

Req R/n

Substituting (i) in (iv).

Reg 4840/n......V)

From Ohm's Law,

V =\Req.. .(vi)

Substituting (V) in (vi),.

220 5 x 4840/n

n= 110

Answer 2

Answer:

Resistance R1 of the bulb is given by the expression,

Supply voltage, V = 220 V

Maximum allowable current, I = 5 A

Rating of an electric bulb P=10watts

Because R=V2/P