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NEET-XII-Physics

33: Thermal and Chemical Effects of Electric Current

with Solutions - page 5
Qstn# iv-24 Prvs-Qstn
  • #24
    A plate of area 10 cm2 is to be electroplated with copper (density 9000 kg m-3) to a thickness of 10 micrometres on both sides, using a cell of 12 V. Calculate the energy spent by the cell in the process of deposition. If this energy is used to heat 100 g of water, calculate the rise in the temperature of the water. ECE of copper = 3 × 10-7 kg C-1 and specific heat capacity of water = 4200 J kg-1
    Ans : Surface area of the plate, A = 10 cm2 = 10 × 10-4 m2
    Thickness of copper deposited, t = 10 μm = 10-5 m
    Density of copper = 9000 kg/m3
    Volume of copper deposited, V = A(2t)
    V = 10 × 10-4 × 2 × 10 × 10-6
    = 2 × 102 × 10-10
    = 2 × 10-8 m3
    Mass of copper deposited, m = Volume × Density = 2 × 10-8 × 9000
    ⇒ m = 18 × 10-5 kg
    Using the formula, m = ZQ, we get:
    18 × 10-5 = 3 × 10-7 × Q
    ⇒ Q = 6 × 102 C
    Energy spent by the cell = Work done by the cell
    ⇒W = VQ
    = 12 × 6 × 102
    = 72 × 102 = 7.2 kJ
    Let ∆θ be the rise in temperature of water. When this energy is used to heat 100 g of water, we have:
    7.2 × 103 = 100 × 10-3 × 4200 × ∆θ
    ⇒ ∆θ = 17 K