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$A)\text{ }99J$

$B)\text{ }90J$

$C)\text{ 1}J$

$D)\text{ 100}J$

Answer

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${{\eta }_{f}}=\dfrac{{{Q}_{2}}}{W}$

Let us write the formula for the efficiency of a refrigerator in terms of the heat energy absorbed from the reservoir at low temperature and the work done on the system.

The efficiency ${{\eta }_{f}}$ of a refrigerator when ${{Q}_{2}}$ amount of heat energy is taken from the reservoir at low temperature and $W$ amount of work is done on the system is given as

${{\eta }_{f}}=\dfrac{{{Q}_{2}}}{W}$ --(1)

Also, the efficiency ${{\eta }_{f}}$ of a refrigerator in terms of its efficiency ${{\eta }_{e}}$ when used as a heat engine is given by

${{\eta }_{f}}=\dfrac{1-{{\eta }_{e}}}{{{\eta }_{e}}}$ --(2)

Now, let us analyze the question.

The work done on a refrigerator system is $W=10J$.

The efficiency of the refrigerator when used as a heat engine is ${{\eta }_{e}}=\dfrac{1}{10}$.

Let the efficiency of the refrigerator be ${{\eta }_{f}}$.

Let the amount of heat energy absorbed from the reservoir at low temperature be ${{Q}_{2}}$.

Therefore, using (1), we get

${{\eta }_{f}}=\dfrac{{{Q}_{2}}}{W}$ --(3)

Also, using (2) we get

${{\eta }_{f}}=\dfrac{1-{{\eta }_{e}}}{{{\eta }_{e}}}$ --(4)

Equating (3) and (4), we get

$\dfrac{{{Q}_{2}}}{W}=\dfrac{1-{{\eta }_{e}}}{{{\eta }_{e}}}$

Putting the values of the variables in the above equation, we get

$\dfrac{{{Q}_{2}}}{10}=\dfrac{1-\dfrac{1}{10}}{\dfrac{1}{10}}=\dfrac{\dfrac{10-1}{10}}{\dfrac{1}{10}}=\dfrac{\dfrac{9}{10}}{\dfrac{1}{10}}=9$

$\therefore {{Q}_{2}}=9\times 10=90J$

Therefore, we have got the heat absorbed from the reservoir at low temperature as $90J$.