12th Science Maharashtra Board
In this category students supposed to ask questions which belong to std 12th maharashtra board Science
- For very high frequency AC supply, a capacitor behaves like a pure conductor. Why ? The reactance of a capacitor is XC = 1/2 π f C , where f is the frequency of the AC supply and C is the capacitance of the capacitor. For ve... 1
- The total impedance of a circuit decreases when a capacitor is added in series with L and R. Explain why ? For an LR circuit, the impedance, Z_LR = sqrtR²+X_L² , where X_L is the reactance of the inductor. When a capacitor of capacitance C is adde... 1
- An electric lamp is connected in series with a capacitor and an AC source is glowing with a certain brightness. Answer: The lamp glows more brightly when the capacitance is increased. For the lamp (resistance R) in series with a capacitor C on an AC su... 1
- A toroidal ring, having 100 turns per cm of a thin wire is wound on a nonmagnetic metal rod of length 1 m and diameter Data : l = 1 m, d = 1 cm, n = 100 cm⁻¹ = 10⁴ m⁻¹, I = 100 A, µ₀ = 4π × 10⁻⁷ H/m The radius of cross section, r = d/2 = 0.5 cm = 5 × 10⁻³ m (... 2
- The primary and secondary coil of a transformer each have an inductance of 200 × 10-6H. Data: L_P = L_S = 2 × 10⁻⁴ H, M = 4 × 10⁻⁶ H M = K sqrtL_P L_S The coupling coefficient is K = fracMsqrtL_P L_S=frac4 × 10⁻⁶sqrt(2 × 10⁻⁴)²=... 1
- A long solenoid of length l, cross-sectional area A and having N1 turns (primary coil) has a small coil of N2 We assume the solenoid to be ideal and that all the flux from the solenoid passes through the outer coil C. For a steady current Is through... 1
- An emf of 96.0 mV is induced in the windings of a coil when the current in a nearby coil is increasing Data: |e₂| = 9.6 × 10⁻² V, dI₁/dt = 1.2 A/s |e₂| = M fracd I₁d t Mutual inductance, M = frac|e₂|d I₁ / d t=frac9.6 × 10⁻²1.2 = 8 × 10⁻² H =... 1
- The value of mutual inductance of two coils is 10 mH. If the current in one of the coil changes Data: M = 10 mH = 10⁻² H, I₁i = 5A, I₁f = 1 A, ∆t = 0.2s The mutually induced emf in coil 2 due to the changing current in coil 1, e₂₁ = -M... 1
- 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