The parallel plates in a capacitor, with a plate area of 9.50 cm2 and an air-filled separation of 3.40 mm, are charged by a 7.60 V battery. They are then disconnected from the battery and pulled apart (without discharge) to a separation of 9.50 mm. Neglecting fringing, find (a) the potential difference between the plates, (b) the initial stored energy, (c) the final stored energy, and (d) the work required to separate the plates.

Explanation:

capacitance of capacitor = ε₀ A / d

ε₀ = 8.85 x 10⁻¹² , A is area of plate and d is plate separation .

= 8.85 x 10⁻¹² x 9.5 x 10⁻⁴ / 3.4 x 10⁻³

C  = 24.73 x 10⁻¹³

capacitance of capacitor after increase in plate separation

= 8.85 x 10⁻¹² x 9.5 x 10⁻⁴ / 9.5  x 10⁻³

= 8.85 x 10⁻¹³

initial charge = capacitance x potential

= 24.73 x 10⁻¹³ x 7.6 C

potential difference after increased separation

= initial charge / increased capacitance

= 24.73 x 10⁻¹³ x 7.6 / (8.85 x 10⁻¹³)

= 21.23 V .

b ) initial stored energy

= 1/2 C V²

= .5 x 24.73 x 10⁻¹³ x 7.6²

= 714.2 x 10⁻¹³ J

c ) final stored energy

1/2 C V²

= .5 x 8.85  x 10⁻¹³ x 21.23 ²

= 1994.4 x 10⁻¹³ J

d ) work done in separation of plate

=2 x  increase in stored energy

=  2 x (1994.4 - 714.2 ) x 10⁻¹³ J

= 2560.4 x 10⁻¹³ J .

the answer is c i did the same question so i know that's right!

the device is called “ rocket engine”