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3. current electricity — Physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 SciencePhysics3. current electricity1 Mark
MCQ
A technician has only two resistance coils. By using them singly, in series or in parallel, he is able to obtain the resistance $3,4,12$ and $16 \,ohms$. The resistance of the two coils are ........... $ohms$
  • A
    $6$ and $10$
  • ✓
    $4$ and $12$
  • C
    $7$ and $9$
  • D
    $4$ and $16$
✓

Answer

Correct option: B.
$4$ and $12$
b
(b)

$\frac{R_1 R_2}{R_1+R_2}=3$

$R_1+R_2=16$

$R_1 R_2=48$

$R_1\left(16-R_1\right)=48$

$R_1^2-16 R_1+48=0$

$R_1=4,12$

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