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 30ŗ with the plates of the capacitor and leaves this space at an angle of 45ŗ 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

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

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

$\frac { 3 } { 2 } \times \frac { 1 } { 2 } \operatorname { mv } _ { 1 } ^ { 2 } = \frac { 1 } { 2 } m v _ { 2 } ^ { 2 }$

K.E_f = $\frac { 3 } { 2 }$ × KE_i

= 1.5 × 100 = 150 eV

p.d. = $\frac { \Delta \mathrm { KE } } { \mathrm { e } }$ = $\frac { 150 - 100 \mathrm { eV } } { \mathrm { e } }$ = 50V