A parallel plate capacitor of area A = 30 cm2 and separation d = 5 mm is charged by a battery of 60-V. If the air between the plates is replaced by a dielectric of κ = 4 with the battery still connected, then what is the ratio of the initial charge on the plates divided by the final charge on the plates?

Respuesta :

Answer:

0.25

Explanation:

A = area of each plate = 30 cm² = 30 x 10⁻⁴ m²

d = separation between the plates = 5 mm = 5 x 10⁻³ m

[tex]C_{air}[/tex] = Capacitance of capacitor when there is air between the plates

k = dielectric constant = 4

[tex]C_{dielectric}[/tex] = Capacitance of capacitor when there is dielectric between the plates

Capacitance of capacitor when there is air between the plates is given as

[tex]C_{air} = \frac{\epsilon _{o}A}{d}[/tex]                            eq-1

Capacitance of capacitor when there is dielectric between the plates is given as

[tex]C_{dielectric} = \frac{k \epsilon _{o}A}{d}[/tex]                            eq-2

Dividing eq-1 by eq-2

[tex]\frac{C_{air}}{C_{dielectric}}=\frac{\frac{\epsilon _{o}A}{d}}{\frac{k \epsilon _{o}A}{d}}[/tex]

[tex]\frac{C_{air}}{C_{dielectric}}=\frac{1}{k}[/tex]

[tex]\frac{C_{air}}{C_{dielectric}}=\frac{1}{4}[/tex]

[tex]\frac{C_{air}}{C_{dielectric}}=0.25[/tex]

Charge stored in the capacitor when there is air is given as

[tex]Q_{air}=C_{air}V[/tex]                             eq-3

Charge stored in the capacitor when there is dielectric is given as

[tex]Q_{dielectric}=C_{dielectric}V[/tex]                             eq-4

Dividing eq-3 by eq-4

[tex]\frac{Q_{air}}{Q_{dielectric}}=\frac{C_{air}V}{C_{dielectric} V}[/tex]

[tex]\frac{Q_{air}}{Q_{dielectric}}=\frac{C_{air}}{C_{dielectric}}[/tex]

[tex]\frac{Q_{air}}{Q_{dielectric}}=0.25[/tex]