JEE Main · 2005 · 08 May 2005 · Offline · Magnetic Effects of Current

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A uniform electric field and a uniform magnetic field are acting along the same direction in a certain region. If an electron is projected along the direction of the fields with a certain velocity then

(A)its velocity will decrease.✓ Correct
(B)its velocity will increase.
(C)it will turn towards right of direction of motion
(D)it will turn towards left of direction of motion.

Answer: (A)

Solution

Projected along both fields, the electron moves parallel to

B

, so

v \times B = 0

and the magnetic field exerts no force. Only the electric force

- e E

remains, and being negative the electron is pushed opposite to

E

, hence opposite to its own motion. This retards it, so its speed steadily decreases.

JEE Main · 2005 · 08 May 2005 · Offline · Single correct option

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