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Moving Charges and Magnetism — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsMoving Charges and Magnetism3 Marks
Question
  1. Write the expression for the force $ \overrightarrow{\text{F}}$ acting on a particle of mass m and charge q moving with velocity $ \overrightarrow{\text{V}} $ in a magnetic field $ \overrightarrow{\text{B}}$ Under what conditions will it move in (i) a circular path and (ii) a helical path?
  2. Show that the kinetic energy of the particle moving in a magnetic field remains constant.
✓

Answer

  1. $ \overrightarrow{\text{F}}=Q(\overrightarrow{\text{V}}\times\overrightarrow{\text{B}})$
  1. When velocity of charged particle and magnetic field are perpendicular to each other.
  2. When velocity is neither parallel nor perpendicular to the magnetic field.
  1. The force, experienced by the charged particle, is perpendicular to the instantaneous velocity $\overrightarrow{V}$ at all instants. Hence the magnetic force cannot bring any change in the speed of the charged particle. Since speed remains constant, the kinetic energy also stays constant.

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