Maharashtra State Board
- Calculate the value of induced emf between the ends of an axle of a railway carriage 1.75 m long traveling Data: l = 1.75 m, v = 50 km/h = 50 × 5/18 m/s. B_v = 5 × 10⁻⁵ T The area swept out by the wing per unit time = 1v. ∴ The magnetic flux cut b... 1
- A stiff semi-circular wire of radius R is rotated in a uniform magnetic field B about an axis passing through its ends. Answer: Amplitude of the emf e₀ = π²R²Bf (taking B perpendicular to the axis of rotation). The semicircular wire, together with the line joi... 1
- A search coil having 2000 turns with area 1.5 cm2 is placed in a magnetic field of 0.60T. The coil is moved Data: N = 2000, A_i = 1.5 × 10⁻⁴ m², A_f = 0, B = 0.6T, ∆t = 0.2s Initial flux, NΦ_f = NBA_i = 2000(0.6)(1.5 × 10⁻⁴) = 0.18 Wb Final flux, N... 1
- In a Faraday disc dynamo, a metal disc of radius R rotates with an angular velocity ω about an axis perpendicular Suppose a thin conducting disc of radius R is rotated anticlockwise, about its axis, in a plane perpendicular to a uniform magnetic field of... 1
- State and explain Lenz’s law in the light of principle of conservation of energy. Lenz’s law : The direction of the induced current is such as to oppose the change that produces it. The change that induces a current may be... 2
- What do you mean by electromagnetic induction? State Faraday’s law of induction. The phenomenon of production of emf in a conductor or circuit by a changing magnetic flux through the circuit is called electromagnetic indu... 1
- The flux rule is the terminology that Feynman used to refer to the law relating magnetic flux to emf. Modern applications of Faraday’s law of induction : Electric generators and motors Dynamos in vehicles Transformers Induction furnaces (indu... 1
- Which property of soft iron makes it useful for preparing electromagnet? An electromagnet should become magnetic when a current is passed through its coil but should lose its magnetism once the current is switched... 1
- What should be retentivity and coercivity of permanent magnet? A permanent magnet should have a large zero-field magnetization and should need a very large reverse field to demagnetize. In other words, i... 1
- What does the hysteresis loop represents? A magnetic hysteresis loop is a closed curve obtained by plotting the magnetic flux density B of a ferromagnetic material against the corres... 1
- Explain one application of electromagnet. Applications of an electromagnet: Electromagnets are used in electric bells, loud speakers and circuit breakers. Large electromagnets are us... 1
- When a plate of magnetic material of size 10 cm × 0.5 cm × 0.2 cm (length , breadth and thickness respectively) Answer: B ≈ 0.635\ T Volume of the plate: V = 10 × 0.5 × 0.2 = 1\ mathrmcm³ = 1×10⁻⁶\ mathrmm³ Magnetisation (magnetic moment per unit volum... 1
- A rod of magnetic material of cross section 0.25 cm2 is located in 4000 Am-1 magnetising field Data: A = 0.25 cm² = 25 × 10⁻⁶ m², H = 4000 A∙m⁻¹, Φ = 25 × 10⁻⁶ Wb Magnetic induction is B = φ/A=frac25 × 10⁻⁶25 × 10⁻⁶ = 1 Wb/m² (a) B = µ... 1
- The work done for rotating a magnet with magnetic dipole momentm, through 90° from its magnetic meridian is n Data : θ₀ = 0°, θ₁ = 90°, θ₂ = 60°, W₁ = nW₂ The work done by an external agent to rotate the magnet from θ₀ to θ is W = MB (cos θ₀ – cos θ)... 1
- An electron in an atom is revolving round the nucleus in a circular orbit of radius 5.3 × 10-11 m, with a speed Data: r = 5.3 × 10⁻¹¹ m, v = 2 × 10⁶ m/s, e = 1.6 × 10⁻¹⁹ C, m_e = 9.1 × 10⁻³¹ kg The orbital magnetic moment of the electron is M₀ = 1/2 ev... 1
- A paramagnetic gas has 2.0 × 1026 atoms/m with atomic magnetic dipole moment of 1.5 × 10-23 A m2 each. Data: N/V = 2.0 × 10²⁶ atoms/m³, μ = 1.5 × 10⁻²³ Am2, T = 27 + 273 = 300 K, B = 3T, k^B = 1.38 × 10⁻²³ J/K, 1 eV = 1.6 × 10⁻¹⁹ J (a) The max... 1
- A magnetic needle placed in uniform magnetic field has magnetic moment of 2 × 10-2 A m2, and moment of inertia Data: M = 2 × 10⁻² A∙m², I = 7.2 × 10⁻⁷ kg∙m², T = 6/10 = 0.6 S T = 2π √(I/M B) The magnitude of the magnetic field is B = frac4 π² IM T² =... 1
- A short bar magnet is placed in an external magnetic field of 700 guass. When its axis makes an angle of 30° Data : B = 700 gauss = 0.07 tesla, θ = 30°, τ = 0.014 N∙m τ = MB sin θ The magnetic moment of the magnet is M = τ/B sin θ=frac(0.014)(0.07)(... 1
- Classify the following atoms as diamagnetic or paramagnetic. H, O, Zn, Fe, F, Ar, He Atoms Electronic configuration No. of Electrons Diamagnetic/Paramagnetic H 1s¹„ 1 Diamagnetic 0 1s²2s²2p⁴ 8 Paramagnetic Zn 1s²2s²2p⁶3s²3p⁶3... 2
- A piece of straight wire has mass 20 g and length 1m. It is to be levitated using a current of 1 A flowing through Data: m = 20 g = 2 × 10⁻² kg, l = 1 m, I = 1 A, g = 9.8 m/s² To balance the wire, the upward magnetic force must be equal in magnitude to th... 1
- Calculate the value of magnetic field at a distance of 2 cm from a very long straight wire Data : I = 5A, a = 0.02 m, fracμ₀4 π = 10⁻⁷ T∙m/A The magnetic induction, B = fracμ₀ I2 π a=fracμ₀4 π 2 I/a = 10⁻⁷ × frac2(5)2 × 10⁻² = 5 ×... 1
- Two wires shown in the figure are connected in a series circuit and the same amount of current of 10 A Data: I₁ = I₂ = 10 A, s = 8 mm = 8 × 10⁻³ m, l = 0.22 m By right hand grip rule, the direction of the magnetic field overrightarrowB₂ due to... 1
- A very long straight wire carries a current 5.2 A. What is the magnitude of the magnetic field Data : I = 5.2 A, a = 0.031 m, fracμ₀4 π = 10⁻⁷ T∙m/A The magnetic induction, B = fracμ₀ I2 π a=fracμ₀4 π 2 I/a = 10⁻⁷ × frac2(5.2)3.1 × 10⁻... 1
- Magnetic field at a distance 2.4 cm from a long straight wire is 16 µT. What must be current through the wire? Data: a = 2.4 × 10⁻² m, B = 1.6 × 10⁻⁵ T, fracμ₀4 π = 10⁻⁷ T∙m/A B = fracμ₀ I2 π a=fracμ₀4 π 2 I/a The current through the wire, I = frac1μ₀... 1