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ISC Class 12 Physics Solved Question Paper 2012

Short Answer Type

21. Three point charges Q₁ = 25μ C, Q₂ = 50μ C, and Q₃ = 100μ C are kept at the comers A, B and C respectively of an equilateral triangle ABC having each side equal to 7.5 m. Calculate the total electrostatic potential energy of the system.

Electrostatic PE of the system:

straight E subscript straight P. straight E end subscript space equals space fraction numerator 1 over denominator 4 πε subscript straight o end fraction open square brackets fraction numerator 25 space straight x 10 to the power of negative 6 end exponent straight x space 50 straight x 10 to the power of negative 6 end exponent over denominator 7.5 end fraction space plus fraction numerator 25 space straight x 10 to the power of negative 6 end exponent straight x space 100 space straight x 10 to the power of negative 6 end exponent over denominator 7.5 end fraction plus fraction numerator 25 space straight x 10 to the power of negative 6 end exponent straight x space 100 space straight x 10 to the power of negative 6 end exponent over denominator 7.5 end fraction space close square brackets straight P. straight E space of space the space system space is comma space straight P. straight E space equals space 9 space straight x 10 to the power of 9 space open square brackets fraction numerator 25 space straight x space 50 straight x 10 to the power of negative 12 end exponent over denominator 7.5 end fraction space plus fraction numerator 25 space straight x space 100 space straight x 10 to the power of negative 12 end exponent over denominator 7.5 end fraction plus fraction numerator 25 space straight x space 100 space straight x 10 to the power of negative 12 end exponent over denominator 7.5 end fraction space close square brackets space space space space space space equals space fraction numerator 9 space straight x 10 to the power of 9 space straight x 10 to the power of negative 12 end exponent over denominator 7.5 end fraction space open square brackets 1250 space plus space 2500 space plus space 5000 close square brackets space space space space space space equals fraction numerator 9 space straight x 10 to the power of negative 3 end exponent over denominator 7.5 end fraction space open square brackets 8750 close square brackets space space space space space space equals space 10.5 space Joules

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22. Obtain and expression for equivalent capacitance C, when three capacitors having capacitance C₁ , C₂ and C₃ are connected in series.

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23. When a potential difference of 3V is applied between the two ends of a 60 cm long metallic wire, current density in it is found to be 1 x 10 ^-7 Am ². Find conductivity of the material of the wire in SI system.

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24. In the circuit shown in Figure 4 below, E is a battery of emf 6V and internal resistance 1Ω. Find the reading of the ammeter A, if it has negligible resistance :

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25. With the help of a neatly drawn and lebelled diagram, obtain balancing condition of a Wheatstone bridge.

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26. State any two differences between Peltier effect and Joule effect.

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27.

Adjecent figure shows a point P near a long conductor XY carrying a current I. MN is a short current carrying conductor, kept at the point P, parallel to the conductor XY.

(i) What is the direction of magnetic flux density ‘B’ at the point P due to the current flowing through XY?

(ii) What is the direction of the force experienced by the conductor MN due to the current flowing through XY?

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28. What the four different types of energy losses in a transformer? State how to reduce/ minimize any one of them.

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29. A 50μ F capacitor, a 30 Ω resistor and a 0.7 H inductor are connected in series to an ac supply which generates an emf ‘e’ given by e = 300 Sin (200t) Volt. Calculate peak value of the current flowing through the circuit

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30. On the basis of Huygen’s wave theory, prove Snell’s law of refraction of light. Draw a neat and lebelled diagram. (Postulates of Huygen’s wave theory not required).

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