#current direction

Doping, Charge Carriers and Conductivity

The direction of conventional current in a forward-biased diode is:

**Charge carriers** in n-type majority electrons, minority holes, in p-type majority holes, minority electrons, minority concentration reduced due to recombination n_e n_h = n_i², doping increases majority, conductivity σ = e(n_e μ_e + n_h μ_h), increases with doping. Donor ionization energy small ~0.01 eV, electrons easily promoted to conduction band at room temperature. In forward bias, current flows from p-side (positive) to n-side (negative) conventionally, as indicated by the diode symbol’s arrow, due to the flow of majority carriers. Substituting values gives P-side to n-side, which matc

Ref: NCERT > Physics Book > Electronic Devices > Doping, Charge Carriers and Conductivity

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Wheatstone Bridge and Meter Bridge

In a Wheatstone bridge, if the bridge is unbalanced, what determines the direction of current through the galvanometer?

**Meter bridge** uses uniform wire of length 1 m, balance length l gives R_unknown = R_known·l/(100-l). Principle same as Wheatstone, with wire resistances proportional to lengths, allowing unknown resistance determination from length ratio. When unbalanced ( R₁ / R₂ neq R₃ / R₄ ), the potentials at the galvanometer’s nodes differ. The current flows from the higher-potential node to the lower one, determined by the relative voltage drops across the bridge arms. Applying I = n e A v_d, R = ρ l/A, R_t = R₀[1+αΔT], Kirchhoff's ΣI=0, ΣV=0, R_eq series/parallel, V = ε - I r and P = I²R, evaluation

Ref: NCERT > Physics Book > Current Electricity > Wheatstone Bridge and Meter Bridge

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Magnetic Force on Moving Charge - Lorentz Force and Motion

Which rule is used to determine the direction of the magnetic field produced by a current-carrying straight wire?

**Lorentz force** on charge q moving with velocity v in magnetic field B is F = q v × B, magnitude F = q v B sinθ, θ angle between v and B (degrees), unit N. Direction perpendicular to both v and B via right-hand rule. When v ⊥ B, motion circular with radius r = m v/(q B), centripetal force provided by magnetic force. The direction of the magnetic field around a current-carrying straight wire is determined by the right-hand rule: grasp the wire with your right hand, thumb pointing in the direction of the current, and your fingers curl in the direction of

Ref: NCERT > Physics Book > Moving Charge and Magnetism > Magnetic Force on Moving Charge - Lorentz Force and Motion

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Torque on Current Loop, Magnetic Moment and Galvanometer

What is the direction of the magnetic field at the center of a circular current-carrying loop?

**Magnetic moment of loop** m = N I A (A·m²), potential energy U = -m·B = -N I A B cosθ, torque tends to align m with B. For square side 0.18 m, A = 0.0324 m², N=30, I=2 A, B=0.4 T, θ=60°, τ =30×2×0.0324×0.4×sin60° =0.7776×0.866=0.673 N·m, illustrating large torque for modest parameters. Using the right-hand rule, if the fingers curl along the direction of the current in the loop, the thumb points perpendicular to the plane of the loop, indicating the field direction at the center. Using F = q v B sinθ, F = I l B sinθ, B = μ₀ I/(2π r),

Ref: NCERT > Physics Book > Moving Charge and Magnetism > Torque on Current Loop, Magnetic Moment and Galvanometer

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Force on Current-Carrying Conductor and Between Parallel Wires

Two parallel wires \( 0.02 \, \text{m} \) apart carry \( 5 \, \text{A} \) each in opposite directions. What is the force

**Force on current-carrying wire** in magnetic field is F = I l × B, magnitude F = I l B sinθ, I current (A), l length (m), B field (T), θ angle between current direction and B. Direction perpendicular to plane containing wire and B, given by Fleming's left-hand rule. f = (μ₀ I₁ I₂/2 π d) . f = (4 π × 10⁻⁷ × 5 × 5/2 π × 0.02) = (100 × 10⁻⁷/0.04) = 2.5 × 10⁻⁵ N/m . Using F = q v B sinθ, F = I l B sinθ, B = μ₀ I/(2π r), B = μ₀ N I/(2R) and

Ref: NCERT > Physics Book > Moving Charge and Magnetism > Force on Current-Carrying Conductor and Between Parallel Wires

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