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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
Assertion : Cyclotron is a device which is used to accelerate the positive ion.

Reason : Cyclotron frequency depends upon the velocity

  • A
    If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
  • B
    If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
  • ✓
    If the Assertion is correct but Reason is incorrect.
  • D
    If both the Assertion and Reason are incorrect.
✓

Answer

Correct option: C.
If the Assertion is correct but Reason is incorrect.
c
Cyclotron is used to accelerate charged partides. So Assertion is correct.

We know that time period of a particle

$\mathrm{T}=\frac{2 \pi \mathrm{r}}{\mathrm{v}_{0}} ; \frac{\mathrm{mv}_{0}^{2}}{\mathrm{r}}=\mathrm{Bqv}_{0} \Rightarrow \mathrm{v}_{0}=\frac{\mathrm{Bqr}}{\mathrm{m}}$

$\mathrm{T}=\frac{2 \pi \mathrm{r}}{\mathrm{Bqr}} \times \mathrm{m}=\frac{2 \pi}{\mathrm{Bq}} \mathrm{m}$

Frequency $=\frac{1}{\mathrm{T}}=\frac{\mathrm{Bq}}{2 \pi \mathrm{m}}$

This does not dpeend upon velocity so Reason is incorrect.

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