Question:
An observer at rest experiences an electric field due to a static charge. Later he starts moving away from it. Then the observer experiences
An observer at rest experiences an electric field due to a static charge. Later he starts moving away from it. Then the observer experiences
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Electric and magnetic fields are frame-dependent quantities. A purely electric field in one inertial frame can appear as a combination of electric and magnetic fields in another frame moving relative to the first.
Updated On: Jun 26, 2026
- Only magnetic field
- Only electric field
- Electric and magnetic field
- No field at all
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The Correct Option is C
Solution and Explanation
Step 1: Field observed in the rest frame of the charge.
A stationary point charge produces only an electric field.
Thus, in the frame where the charge is at rest, \[ \vec{B}=0, \] and \[ \vec{E}\neq 0. \] Therefore, an observer initially at rest experiences only the electric field.
Step 2: Consider the observer moving away from the charge.
When the observer starts moving, the charge appears to be moving relative to the observer.
According to the theory of special relativity, electric and magnetic fields transform into one another when viewed from different inertial frames.
A moving charge constitutes an electric current and hence produces a magnetic field in the observer's frame.
Step 3: Fields in the moving observer's frame.
Since the charge is now seen as moving, \[ \vec{E}'\neq 0 \] and \[ \vec{B}'\neq 0. \] Thus, the observer experiences both electric and magnetic fields simultaneously.
Step 4: Final conclusion.
Therefore, a moving observer experiences \[ \boxed{\text{Electric and magnetic fields}} \] Hence, the correct option is \[ \boxed{(3)} \]
A stationary point charge produces only an electric field.
Thus, in the frame where the charge is at rest, \[ \vec{B}=0, \] and \[ \vec{E}\neq 0. \] Therefore, an observer initially at rest experiences only the electric field.
Step 2: Consider the observer moving away from the charge.
When the observer starts moving, the charge appears to be moving relative to the observer.
According to the theory of special relativity, electric and magnetic fields transform into one another when viewed from different inertial frames.
A moving charge constitutes an electric current and hence produces a magnetic field in the observer's frame.
Step 3: Fields in the moving observer's frame.
Since the charge is now seen as moving, \[ \vec{E}'\neq 0 \] and \[ \vec{B}'\neq 0. \] Thus, the observer experiences both electric and magnetic fields simultaneously.
Step 4: Final conclusion.
Therefore, a moving observer experiences \[ \boxed{\text{Electric and magnetic fields}} \] Hence, the correct option is \[ \boxed{(3)} \]
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