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4. Moving charges and magnetism — Physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 SciencePhysics4. Moving charges and magnetism1 Mark
MCQ
The magnetic induction at a point $P$ which is distant $4\, cm$ from a long current carrying wire is ${10^{ - 8}}\,Tesla$. The field of induction at a distance $12\, cm $ from the same current would be
  • ✓
    $3.33 \times {10^{ - 9}}\,Tesla$
  • B
    $1.11 \times {10^{ - 4}}\,Tesla$
  • C
    $3 \times {10^{ - 3}}\,Tesla$
  • D
    $9 \times {10^{ - 2}}\,Tesla$
✓

Answer

Correct option: A.
$3.33 \times {10^{ - 9}}\,Tesla$
a
(a) $B = \frac{{{\mu _0}}}{{4\pi }} \cdot \frac{{2i}}{r}$

$==>$ $\frac{{{B_1}}}{{{B_2}}} = \frac{{{r_2}}}{{{r_1}}}$

$==>$ $\frac{{{{10}^{ - 8}}}}{{{B_2}}} = \frac{{12}}{4}$
$==>$ ${B_2} = 3.33 \times {10^{ - 9}}\,Tesla$

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