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

Options

A. will turn towards right of direction of motion
B. speed will decrease
C. speed will increase
D. will turn towards left direction of motion.

Answer

b

Explanation

Magnetic force on the electron will be
`vecF_(m) = - e ( vec v xx vec B) rArr F_(m) = evB sin 0^(@) = 0 `
Electric force on the electron will be
`vecF_(e) = - e vec E`
Since the force is directed opposite to the velocity of electron, therefore, the speed will decrease.