Two large metal plates of area 1.2 m^2 face each other, 6.5 cm apart, with equal charge magnitudes but opposite signs. the field magnitude e between them (neglect fringing) is 68 n/c. find |q|.

Q= 722.5 *10⁻¹² C

Explanation:

Conceptual analysis

For a parallel plate capacitor, we can use the following formula :

E= (Q) /(ϵ₀*A)  Formula (1)

Where:

E: electric field between the plates ( N/C)

Q: Charge of  the plates (C)

ϵo : vacuum permittivity  ( C²/ N.m²)

A :  area oh the plates (m²)

Known data

A = 1.2 m²

E= 68 N/C

ϵo= 8.8542*10⁻¹² (  C²/ N.m²)

Problem development

We apply the formula (1) :

Q= (68) (8.8542*10⁻¹²)(1.2)

Q= 722.5 *10⁻¹² C

when a device is used in a circuit in which the voltage is 81 v, the current flowing through the device is 3 a. what is the resistance of the device?

a. 27 ω

b. 40.5 a

c. 243 ω

d. 243 a

the correct answer is a. 27

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