#magnetic field direction

Induced EMF Due to Change in Magnetic Field

A flat coil is placed in a magnetic field that decreases with time. The direction of the induced current is such that it

**Induced emf due to B change** e = -N A dB/dt, N turns, A area (m²), dB/dt rate of change of field (T/s). For 110 turns area 0.035 m² B 0.09 T to 0 in 0.5 s, dB/dt=0.18 T/s, e=110×0.035×0.18=0.693 V, direction opposes decrease via Lenz's law. Lenz’s law dictates that the induced current opposes the decrease in flux by producing a magnetic field in the same direction as the original field. Using Φ = B A cosθ, e = -N dΦ/dt = -N A dB/dt = B l v = N B A ω sinωt, L = μ₀ N²A/l, M = e/(dI/dt) and U

Ref: NCERT > Physics Book > Electromagnetic Induction > Induced EMF Due to Change in Magnetic Field

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EM Wave Characteristics - Transverse Nature and E/B Ratio

In an electromagnetic wave, if the electric field oscillates along the \( y \)-axis and the wave propagates along the \(

**EM wave in vacuum** transverse, E and B perpendicular to propagation and to each other, E×B along propagation, in phase, E/B = c =3×10⁸ m/s, c =1/√(μ₀ ε₀), μ₀=4π×10⁻⁷ H/m, ε₀=8.85×10⁻¹² F/m. For E₀=45 V/m, B₀=E₀/c=45/3×10⁸=1.5×10⁻⁷ T=150 nT, illustrating B much smaller than E. In an EM wave, E , B , and the direction of propagation are perpendicular. If E is along y -axis and propagation is along x -axis, then B must be along z -axis ( E × B gives propagation direction). Using c = fλ, E₀/B₀ = c, I_d = ε₀ dΦ_E/dt, and spectrum classification λ = c/f, evaluation yields z

Ref: NCERT > Physics Book > Electromagnetic Waves > EM Wave Characteristics - Transverse Nature and E/B Ratio

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EM Wave Characteristics - Transverse Nature and E/B Ratio

An electromagnetic wave propagates in the \( z \)-direction with electric field along the \( x \)-axis. In which directi

**EM wave in vacuum** transverse, E and B perpendicular to propagation and to each other, E×B along propagation, in phase, E/B = c =3×10⁸ m/s, c =1/√(μ₀ ε₀), μ₀=4π×10⁻⁷ H/m, ε₀=8.85×10⁻¹² F/m. For E₀=45 V/m, B₀=E₀/c=45/3×10⁸=1.5×10⁻⁷ T=150 nT, illustrating B much smaller than E. In an electromagnetic wave, E , B , and the direction of propagation are mutually perpendicular. If E is along x -axis and propagation is along z -axis, then B must be along the y -axis (since E × B gives the direction of propagation). Using c = fλ, E₀/B₀ = c, I_d = ε₀ dΦ_E/dt, and spectrum classification λ =

Ref: NCERT > Physics Book > Electromagnetic Waves > EM Wave Characteristics - Transverse Nature and E/B Ratio

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Hysteresis, Retentivity, Coercivity and Permanent Magnets

The magnetic field inside a bar magnet is directed from:

**Soft ferromagnetic materials** have low coercivity and retentivity, narrow hysteresis loop, lose magnetism when external field removed, ideal for electromagnets and transformer cores. Energy loss per cycle proportional to loop area, explaining why soft materials minimize loss. Inside a bar magnet, magnetic field lines run from the south pole to the north pole to form closed loops with the external field (north to south), maintaining continuity as there are no magnetic monopoles. Substituting values gives South to north, which matches expected magnitude for this magnetic configuration, confir

Ref: NCERT > Physics Book > Magnetism and Matter > Hysteresis, Retentivity, Coercivity and Permanent Magnets

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