Question

A narrow electron beam passes undeviated through an electric field $E = 3 \times 10 ^ { 4 }$ volt $/ \mathrm { m }$and an overlapping magnetic field . If electric field and magnetic field are mutually perpendicular. The speed of the electrons is.

• A. 60 m/s
• B. $10.3 \times 10 ^ { 7 } \mathrm {~m} / \mathrm { s }$
• C. $1.5 \times 10 ^ { 7 } \mathrm {~m} / \mathrm { s }$
• D. $0.67 \times 10 ^ { - 7 } \mathrm {~m} / \mathrm { s }$

Answer 1

Answer: (C)

$1.5 \times 10 ^ { 7 } \mathrm {~m} / \mathrm { s }$

Answer 2

$e E = e v B \Rightarrow v = \frac { E } { B } = \frac { 3 \times 10 ^ { 4 } } { 2 \times 10 ^ { - 3 } } = 1.5 \times 10 ^ { 7 } \mathrm {~m} / \mathrm { s }$