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Capacitor
- 1. CAPACITOR Dr. Nadeem Khalid AL-AQSA ACADEMY, LAHORE
- 2. • Definition • The device which is used to store electric charge is called capacitor CAPACITOR
- 4. • A simple capacitor consist of two parallel conducting plates separated by air, or some insulating medium is called parallel plate capacitor • The insulating medium is known as dielectric PARALLEL PLATE CAPACITOR
- 5. • If the plates are connected to a battery of voltage V the one of the plate has + Q charge and the other plate have – Q charge. These charges remain on the inner surface of the plates due to attraction between the opposite charges • It is observed that if the amount of charge stored increased the potential difference between plates also increase • Q∝ 𝑉 • Q = CV • C = 𝑄 𝑉 • Here C is the constant of proportionality called capacitance of capacitor CHARGING OF CAPACITOR
- 6. • Definition • The capacity of a capacitor to store charges is known as Capacitance • Formula • C = 𝑄 𝑉 • Dependence • Area of plate • Distance between plates • Medium present between plates • Units • Farad(F) • Farad • if one coulomb charge store on capacitor plates produce a potential difference of one volt then capacitance of this capacitor will be one farad • 1 farad = 1 𝑐𝑜𝑢𝑙𝑜𝑚𝑏 1 𝑣𝑜𝑙𝑡 CAPACITANCE
- 7. • Consider a parallel plate capacitor. Let • A = area of each plate • d = distance between the plates • Q = charge store on each plate • V = potential difference between plates • E = electric field • 𝜎 = surface charge density CAPACITANCE OF A PARALEL PLATE CAPACITOR
- 8. • Capacitance when air or vacuum between plates • Cvac = 𝑄 𝑉 …….(1) • Cvac = 𝜎𝐴 𝜎𝑑 ϵ0 • Cvac = 𝐴ϵ0 d CAPACITANCE OF A PARALEL PLATE CAPACITOR E= 𝑽 𝒅 V = Ed E = 𝝈 𝛜 𝟎 V = = 𝝈𝒅 𝛜 𝟎 𝝈= 𝑸 𝑨 Q = 𝝈𝑨
- 9. • Capacitance with dielectric as medium • If an insulating material of relative permittivity ϵr is placed between plates the capacitance of capacitor is increased by the factor ϵr called as dielectric constant • Cmed = 𝐴ϵ0 ϵr d CAPACITANCE OF A PARALEL PLATE CAPACITOR
- 10. • How capacitance increase • C = 𝑄 𝑉 • by placing dielectric voltage decrease so capacitance increase • Dielectric constant • Ratio of capacitance of a parallel plate capacitor with a dielecric to its capacitance with vacuum or air as a medium • ϵr = Cmed Cvac CAPACITANCE OF A PARALEL PLATE CAPACITOR
- 12. PRACTICE TEST Answer: A C = 𝑄 𝑉
- 13. PRACTICE TEST Answer: A Cmed = 𝐴ϵ0 ϵr d
- 14. PRACTICE TEST Answer: C Cvac = 𝑨𝛜 𝟎 𝒅