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Mention the three states by which matter exists.

Physics

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Step-by-step solution

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None of the three situations result in motional emf.

  1. Situation (a) – A positively charged dry cloth is rubbed on a piece of paper which is cut into the shape of a loop.

    Rubbing produces static electric charge via friction (triboelectric effect). Placing the charged cloth near the paper loop causes electrostatic induction: opposite charges separate on the loop.
    No magnetic field is present. No conductor motion in a magnetic field. No change in magnetic flux.
    No motional emf (ϵ=0\epsilon = 0).

  2. Situation (b) – A charged loop is placed in a uniform magnetic field ⊗\otimes (into the page).

    The loop is stationary. Magnetic field is static and uniform.
    Magnetic flux ΦB=B⋅Acos⁡0∘=BA\Phi_B = B \cdot A \cos 0^\circ = B A is constant (no motion, no change in BB).
    Faraday's law: induced emf ϵ=−dΦBdt=0\epsilon = -\frac{d\Phi_B}{dt} = 0.
    Charge on loop does not produce emf. No velocity v\mathbf{v}.
    No motional emf (ϵ=0\epsilon = 0).

  3. Situation (c) – The page (loop) on which writing is done is moving towards north.

    Earth's magnetic field: horizontal component Bh≈0.3B_h \approx 0.3–0.4 gauss towards magnetic north; vertical component BvB_v downward. Field approximately uniform over small loop.
    Loop translates with velocity v\mathbf{v} towards north (parallel to BhB_h).
    For translational motion of rigid loop in uniform B\mathbf{B}, magnetic flux ΦB\Phi_B constant (area and B⊥B_\perp unchanged).
    Motional emf ϵ=∮(v×B)⋅dl=0\epsilon = \oint (\mathbf{v} \times \mathbf{B}) \cdot d\mathbf{l} = 0 (closed path, conservative field).
    No motional emf (ϵ=0\epsilon = 0).

    None

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