NTSE Stage 2 SAT 2018 Exam Question Paper

Question : 39 of 100

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Three electric bulbs of rating 40 W – 200 V; 50 W – 200 V and 100 W – 200 V are connected in series to a 600 V supply. What is likely to happen as the supply is switched on?

Only 50 W bulb will fuse
Both 40 W and 50 W bulbs will fuse.
All the three bulbs will emit light with their rated powers.
100 W bulb will emit light of maximum intensity.

Validate

Solution:

Resistance of 40 W – 200 V, 50 W – 200 V, 100 W – 200 V arerespectively

{R}_{40}=\;\;{V^{2}}/{P_{40}}=\;\;{200×200}/{40}=1000Ω

{R}_{50}=800Ω

and

{R}_{100}=400Ω

I=\;\;{600}/{100+800+400}=\;\;{600}/{2200}=0.2727{A}

{I}_{40}=\;\;{P_{1}}/{V}=\;\;{40}/{200}=0.2{A}

{I}_{{50}}=\;\;{P_{2}}/{V}=\;\;{50}/{200}=\;\;{5}/{20}=0.25{A}

{I}_{100}=\;\;{P_{3}}/{V}=\;\;{100}/{200}=.5{A}

Clearly, 0.2 A & 0.25 A < 0.27 A hence both 40 W and 50 W bulbs will fuse.

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