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ISC Class 12 Physics Solved Question Paper 2007

Short Answer Type

21. Derive an expression for the capacitance of a parallel plate capacitor in terms of the areas of the plates and the distance between them. Assume there is a vacuum in between the plates with the electric field between the plates E = σ/ ε₀. (where the symbols have their usual meaning.)

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22. Three equal charges of 5.0 μC each are placed at the three vertices of an equilateral triangle of side 5.0 cm each. Calculate the electrostatic potential energy of the system of charges.

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23. Define the emf of a cell in terms of the work done in moving a charge through the cell. Using Joule’s law obtain the equation, emf = 1(R + r). (The symbols have their usual meaning.)

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24. (i) State one important difference between the Joule effect and the Peltier effect.

ii) The principle of a deflection magnetometer is expressed by the formula B_m = B_H tan θ. What is represented by the symbol B_m and B_H?

i) One important difference between the Joule effect and Peltier effect is that Joule effect takes place throught out the metal with the production of heat whereas Peltier effect takes place only at junction with either production or absorption of heat.

(ii) In formula B_m = B_H tan θ

B_m→ Magnetic field produced by the magnet placed on one of the arms of the deflection magnetometer.

B_H → Horizontal component of Earth’s magnetic

field.

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25.

Obtain the formula, I = k θ for a moving coil galvanometer, given, the deflecting torque where m is the magnetic dipole moment of the coil placed in the magnetic field B, I is the current in the galvanometer and θ is the deflection.

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26.

(i) Define the terms magnetization (M) and magnetic susceptibility (x_m).

(ii) What is the value of the magnetic susceptibility of aluminium if its relative permeability is 1.000022 ?

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27. Obtain the relation for the current I = I₀ sin (ωt - π/2) for a pure inductor across which an alternating emf ε = ε₀ sin ψt is applied.

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28. A resistance of 150 Ω and capacitance of 15 μ F are connected in series with an AC source. The peak value of the current is 0.20 A. Calculate the average power consumed in the circuit. If the capacitor is removed but the current is kept the same, what is the average power consumed in the resistor alone ?

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29. In ac circuit resistance R, inductance I, and capacitance C are connected in series. The value of C is adjusted for resonance. State any three properties of this circuit which hold true for resonance only. (Give the properties in words or equations, relating X_L, Xc, Z, R, φ, power etc.)

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