Question

An electron with a kinetic energy of 100 eV enters the space between the plates of plane capacitor made of two dense metal grids at an angle of 30⁰ with the plates of capacitor and leaves this space at an angle of 45⁰ with the plates. What is the potential difference of the capacitor –

• A. 100 V
• B. 50 V
• C. 150 V
• D. 200 V

Answer 1

Answer: (B)

50 V

Answer 2

Horizontal velocity is constant

v₁ cos 30⁰ = v₂ cos 45⁰

v₁ $\frac { \sqrt { 3 } } { 2 }$ = v₂ × $\frac { 1 } { \sqrt { 2 } }$

$\frac { 3 v _ { 1 } ^ { 2 } } { 4 }$ =

=

KE_f = $\frac { 3 } { 2 }$× KE_i

= 1.5 × 100 = 150 eV

P.d. = $\frac { \Delta \mathrm { KE } } { \mathrm { e } }$ = = 50 V