Answer:
a ) 2.13 X 10⁶ m/s .
b ) 1.28 X 10⁶ m/s
Explanation:
When electrons are repelled by negative plates and attracted by positive plates , it will increase their kinetic energy.
Increase in their energy = 4.15 eV
= 4.5 X 1.6 X 10⁻¹⁹ J
= 6.64 x 10⁻¹⁹ J
Initial kinetic energy
= 1/2 mv²
= 1/2 x 9.1 x 10⁻³¹ x ( 1.76 x 10⁶)²
= 14.09 X 10⁻¹⁹ J
Total energy
= 6.64 x 10⁻¹⁹+14.09 X 10⁻¹⁹
= 20.73 x 10⁻¹⁹
If V be the increased velocity
1/2 m V² = 20.73 X 10⁻¹⁹
.5 X 9.1 X 10⁻³¹ V² = 20.73 X 10⁻¹⁹
V = 2.13 X 10⁶ m/s .
b ) When electrons are released from positive plate , their speed are reduced because of attraction between electrons and positively charge plates.
Initial kinetic energy
= 14.09 x 10⁻¹⁹ J (see above )
reduction in kinetic energy
= 6.64 x 10⁻¹⁹ J ( See above )
Total energy with electron -
= 14.09 x 10⁻¹⁹ - 6.64 x 10⁻¹⁹
= 7. 45 x 10⁻¹⁹ J .
If V be the energy of electrons reaching the negative plate,
1/2 m V² =7. 45 x 10⁻¹⁹
V = 1.28 X 10⁶ ms⁻¹
