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  • A    source is connected to a  <img alt="\mathrm{25V,5 W}" sr

A  \mathrm{200V,50Hz AC}  source is connected to a  \mathrm{25V,5 W}  lamp and an addition resistance \mathrm{R} in series ( as shown in figure ) to run the lamp at its peak brightness, then the value of \mathrm{R} ( in ohm ) will be __________.

Option: 1

975


Option: 2

-


Option: 3

-


Option: 4

-


Answers (1)

best_answer

For its peak brightness, the actual voltage lamp has to be \mathrm{25V}.

Resistance of lamp    \mathrm{ R_{1} }\mathrm{=\frac{V^{2}}{P}=\frac{25 \times 25}{5}=125 \Omega}

                                                                       

Voltage across lamp    \mathrm{V_{1}=\frac{V \times R_{1}}{R_{1}+R_{2}} }\\

                                   \mathrm{25=\frac{220 \times 125}{125+R}} \\

                                   \mathrm{125+R=260 \times 5=1100} \\

                                   \mathrm{R=1100-125} \\

                                   \mathrm{R=975 \Omega}

Posted by

Gaurav

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