Given below are two statements :
Statement I : The electric force changes the speed of the charged particle and hence changes its kinetic energy; whereas the magnetic force does not change the kinetic energy of the charged particle.
Statement II : The electric force accelerates the positively charged particle perpendicular to the direction of electric field. The magnetic force accelerates the moving charged particle along the direction of magnetic field.
In the light of the above statements, choose the most appropriate answer from the options given below :

Solution

Physics sir · 3 steps

Check where each force points: electric along the field, magnetic always perpendicular to both v and B.

1. F⃗ = qE⃗ + q(v⃗ × B⃗)

2. Statement I. The electric force qE⃗ can have a component along the velocity, so it does work and changes speed and kinetic energy. The magnetic force q(v⃗ × B⃗) is always perpendicular to v⃗, so its power F⃗ · v⃗ is zero and the kinetic energy stays the same. Statement I is correct.
3. Statement II. For a positive charge, qE⃗ points along E⃗, not perpendicular to it. The magnetic force comes from a cross product, so it is perpendicular to B⃗, never along it. Both halves of the statement are reversed, so Statement II is incorrect.
4. So. Statement I is correct and Statement II is incorrect, which is option (c).

The idea to keep. Electric force acts along E⃗ and can change speed. Magnetic force is a cross product, perpendicular to both v⃗ and B⃗, so it bends the path but never does work.

Answer from the NTA final answer key. Solution by PrepWiser.