Sign in
12thPass logo
New chatPYQ LibraryDoubtsRank report
Sign in to see Recents

Your guest activity stays on this device

Sign in to save progress →
Sign in

Current Electricity question

2003 · Q133
Guest · filters and generic practice availableBrowsing as a guest · PYQ filters and generic practice are available. Sign in only for personalised features and saved progress.
  1. PYQ Library
  2. /NEET
  3. /Physics
  4. /Current Electricity
  5. /2003 · Q133

Current Electricity question

2003 · Q133

NEETPhysicsCurrent ElectricityMCQ+4 / −1
An electric kettle has two heating coils. When one of the coils is connected to an a.c. source, the water in the kettle boils in 10 minutes. When the other coil is used the water boils in 40 minutes. If both the coils are connected in parallel, the time taken by the same quantity of water to boil will be
  1. A
    8 minutes
  2. B
    4 minutes
  3. C
    25 minutes
  4. D
    15 minutes
View written solutionFree

Correct answer: A

Let R1 and R2 be the resistance of the two coils and V be the voltage supplied.

Effective resistance of two coils in parallel = R1R2R1+R2{{{R_1}{R_2}} \over {{R_1} + {R_2}}}R1​+R2​R1​R2​​

Let H be the heat required to begin boiling in kettle.

Then H = Power ×\times× time = V2t1R1=V2t2R2{{{V^2}{t_1}} \over {{R_1}}} = {{{V^2}{t_2}} \over {{R_2}}}R1​V2t1​​=R2​V2t2​​

For parallel combination, H = V2(R1+R2)tpR1R2{{{V^2}\left( {{R_1} + {R_2}} \right){t_p}} \over {{R_1}{R_2}}}R1​R2​V2(R1​+R2​)tp​​

⇒1tp=(t2+t1t2t1) \Rightarrow {1 \over {{t_p}}} = \left( {{{{t_2} + {t_1}} \over {{t_2}{t_1}}}} \right)⇒tp​1​=(t2​t1​t2​+t1​​)

∴tp=t2t1t2+t1=10×4010+40=8 \therefore {t_p} = {{{t_2}{t_1}} \over {{t_2} + {t_1}}} = {{10 \times 40} \over {10 + 40}} = 8∴tp​=t2​+t1​t2​t1​​=10+4010×40​=8 minute

PreviousNext

More from Current Electricity

  • Specific resistance of a conductor increases with2002 · MCQ
  • For a cell terminal potential difference is 2.2V when circuit is open and reduce to 1.8 V when cell is connected to a resistance of R = 5 Ω. Determine internal resistance of cell (r)2002 · MCQ
  • If specific resistance of a potentiometer wire is 10-7Ω m and current flow through it is 0.1 amp., cross-sectional area of wire is 10−6 m2 then potential gradient will be2001 · MCQ
  • The resistance of each arm of the Wheatstone's bridge is 10 ohm. A resistance of 10 ohm is connected in series with a galvanometer then the equivalent resistance across the battery will be2001 · MCQ
  • Copper and silicon is cooled from 300 K to 60 K , the specific resistance2001 · MCQ
  • The net resistance of the circuit between A and B is Includes diagram2000 · MCQ
  • A car battery of emf 12 V and internal resistance 5×10−2 Ω., receives a current of 60 amp, from external source, then terminal potential difference of battery is2000 · MCQ
  • Two bulbs of (40 W, 200 V), and (100 W, 200 V). Then correct relation for their resistances2000 · MCQ