4. [1pt] A uniform magnetic field is directed into the page. Because of the pres

Question

4. [1pt] A uniform magnetic field is directed into the page. Because of the presence of a tenuous gas in the region, a charged particle moving in the plane of the page follows an anti-clockwise spiral of decreasing radius as shown x X (For each statement select T True, F False) A) The charge is negative. B) The acceleration vector of the particle is constant. C) The magnitude of the momentum of the particle is increasing. D) The magnetic force is doing exactly zero work on the charge at all times E) The charge is slowing down.

Explanation / Answer

(A) path is anticlockwise and field is into the page.

so charge is +ve.

False

(B) r = m v / q B

and a = v^2 / r = q B v / m

v is decreasing hence acceleration is also decreasing.

False

(C) p = m v r = m (q r B / m)(r) = q r^2 B

r -> decreasing

so p -> decreasing

False

(D) magnetic force is perpendicular so its work done will be zero.

True

(E) v is decreasing. hence slowing down.

True

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