A 500 W heating unit is designed to operate from a 115 volt line. If the line voltage drops to 110 volt, the percentage drop in heat output will be

  • Option 1)

    10.2%

  • Option 2)

    8.1%

  • Option 3)

    8.6%

  • Option 4)

    7.6%

 

Answers (1)
V Vakul

As we learnt in

Power dissipiated in external resistance -

P=(\frac{E}{R+r})^{2}R

-

 

 P_{i}=\frac{v_{i}^{2}}{R}= \frac{\left ( 115 \right )^{2}}{R} - - -- - -- - (1)

P_{f}=\frac{v_{f}^{2}}{R}= \frac{\left ( 110 \right )^{2}}{R}

Change =\frac{P_{i}-P_{f}}{P_{i}}= 1-\frac{P_{f}}{P_{i}}= 1-\left ( \frac{110}{115} \right )^{2}

              =\frac{5\times 225}{115 \times 115}=8.5\%

 


Option 1)

10.2%

Incorrect

Option 2)

8.1%

Incorrect 

Option 3)

8.6%

Correct 

Option 4)

7.6%

Incorrect 

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