Question

Two long concentric cylindrical conductors of radii a & b (b < a) are maintained at a potential difference V & carry equal & opposite currents I. An electron with a particular velocity "U" parallel to the axis will travel undeviated in the evacuated region between the conductors. Then U=

• A.
• B.
• C.
• D.

Answer 1

Answer: (B)

Answer 2

E = p.d. V = $\frac { \lambda } { 2 \pi \varepsilon _ { 0 } } \ln \left( \frac { \mathrm { a } } { \mathrm { b } } \right)$ E = B varies with r B = $\frac { \mu _ { 0 } \mathrm { I } } { 2 \pi \mathrm { r } }$ B & E are perpendicular to each other

\ qUB = qE (if particle travel undeviated)

U = $\frac { E } { B } = \frac { 2 \pi V } { \mu _ { 0 } \mathrm { I } \ln \left( \frac { a } { b } \right) }$