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27 September, 09:32

a parallel plate capacitor has square plates that have edge length equal to 100cm and are separated by 1 mm. It is connected to a battery and is charged to 12V. How much energy is stored in the capacitor?

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Answers (2)
  1. 27 September, 09:35
    0
    3.187*10⁻⁷ J.

    Explanation:

    The expression for the energy stored in a capacitor is given as,

    E = 1/2CV² ... Equation 1

    Where E = Energy stored in the capacitor, C = Capacitance of the capacitor, V = Voltage.

    But,

    C = ε₀A/d ... Equation 2

    Where A = Area of the plates, d = distance of separation of the plates, ε₀ = permitivity of free space

    Substitute equation 2 into equation 1

    E = 1/2 (ε₀A/d) V² ... Equation 3

    Given: V = 12 V, d = 1 mm = 0.001 m

    Note Edge length is the diagonal of a square

    From Pythagoras,

    L²+L² = d

    Where d = diagonal = 100 cm = 1 m

    2L² = 1

    L² = 1/2

    L = √ (1/2) m

    A = area of a square = L², where L = Length of the square plates = √ (1/2)

    A = [√ (1/2) ]² = 1/2 m², ε₀ = 8.854*10⁻¹² F/m

    Substitute into equation 3

    E = 1/2 (8.854*10⁻¹²*1/2/0.001) 12²

    E = 36 (8854*10⁻¹²)

    E = 318744*10⁻¹²

    E = 318744*10⁻⁷ J.

    Hence the amount of energy stored in the capacitor = 3.187*10⁻⁷ J.
  2. 27 September, 09:47
    0
    the energy is stored in the capacitor is 0.32 μJ

    Explanation:

    Given;

    distance of separation, d = 1 mm = 0.001 m

    edge length of the square = 100 cm

    potential difference across the plates, V = 12 v

    let the side of the square = L

    This edge length is also the diagonal of the square which makes a right angle with the side of the square.

    Applying Pythagoras theorem;

    L² + L² = 100²

    2L² = 100²

    L² = 100²/2

    Note area of a square is L²

    A = L² = 100²/2 = 5000 cm²

    A (m²) = 5000 cm² x 1m² / (100 cm) ²

    A = 5000 cm² x 1m²/10000 cm²

    A = 0.5 m²

    Energy stored in a parallel plate capacitor, E = ¹/₂CV²

    C = ε₀A/d

    where;

    ε₀ is permittivity of free space = 8.85 x 10⁻¹² F/m

    d is the distance of separation = 0.001 m

    A is the area of the plate

    C = ε₀A/d = (8.85 x 10⁻¹²) x0.5 / 0.001

    C = 4425 x 10⁻¹² F

    E = ¹/₂CV² = ¹/₂ x 4425 x 10⁻¹² x (12) ²

    E = 318600 x 10⁻¹² = 0.32 μJ

    Therefore, the energy is stored in the capacitor is 0.32 μJ
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