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NEET 2009 (AIPMT) · Moving Charge in a Magnetic Field

Moving Charge in a Magnetic Field question from NEET 2009 (AIPMT)

Q109NEET 2009 · AIPMTEasy

Moving Charge in a Magnetic Field

The magnetic force acting on a charged particle of charge −- 2 μ\muC in a magnetic field of 2 T acting in y direction, when the particle velocity is (2i^+3j^)×106 ms−1\left(2\hat{i} + 3\hat{j}\right) \times 10^{6}\ ms^{-1}, is

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Answer: (d)

  1. F⃗=q(v⃗×B⃗)\vec{F} = q(\vec{v} \times \vec{B}) with B⃗=2j^\vec{B} = 2\hat{j} T.
  2. v⃗×B⃗=(2i^+3j^)×106×2j^=4×106k^\vec{v} \times \vec{B} = (2\hat{i} + 3\hat{j}) \times 10^6 \times 2\hat{j} = 4 \times 10^6 \hat{k} (since j^×j^=0\hat{j} \times \hat{j} = 0).
  3. F⃗=−2×10−6×4×106k^=−8k^\vec{F} = -2 \times 10^{-6} \times 4 \times 10^6 \hat{k} = -8\hat{k} N
  4. So the answer is (d) 8 N in −z-z direction.
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