Question

Out of two bulbs 50W-220V and 100W-220V, which one will glow brighter:- a) when connected in series b) when connected in parallel .

Answer 1

a.
Series connection Since in series, the flow of current is constant. We need to compare power with ‘R’.

P = V × I

⇒ P = V2R

RA = 200250 = 800 Ω

RB = 2002100 = 400 Ω

Since, current is constant in P = i2 R. More the resistance more will be the power and thus, the bulb glows more brightly.

Hence, Bulb A glows more.
​​​​​​
b.
​​​​​​When connected in parallel voltage will be constant

When voltage is constant then P = V2R

P ∝ 1R so when R↑ power↓ and viceversa

Bulb A: P = V2R


​​​​​​⇒
RA ​= V2P = 220250 = 968

Bulb B: P = V2R
⇒
RB​ = V2P = 2202100 = 484

So, RB​ < RA​

⇒ PB​ > PA​

⇒ Bulb B will glow brightly