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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.

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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).

On the basis of Huygen's wave theory, the laws of refraction

Given : AEB is the incident wave front and DGC be the refracted wavefront.

BC = V₁t V₁ = velocity of light in medium 1.

AD = V₂t V₂ = velocity of light in medium 2.

i) Existence of the refracted wave front DGC

$BC over straight V subscript 1 equals fraction numerator E F over denominator V subscript 1 end fraction plus fraction numerator F G over denominator V subscript 2 end fraction$

ii) $fraction numerator sin space straight i over denominator sin space straight r end fraction space equals space V subscript 1 over V subscript 2$

Construction : From the point F a perpendicular FH is dropped.

Proof: ΔABC + ΔFHC [By simple geometry these triangles are similar (A.A.A.)]

$BC over HC space equals space fraction numerator A C over denominator F C end fraction space space space space space space space space... space left parenthesis i right parenthesis I n space increment A D C space plus space increment F G C comma space space space space fraction numerator A C over denominator F C end fraction space equals space fraction numerator A D over denominator F G end fraction space space space space space... space left parenthesis i i right parenthesis thin space space space space space space space space space space space space space space space space space space space space space space space space space space space space left square bracket Similar space by space AAA right square bracket From space eqns. space left parenthesis straight i right parenthesis space and space left parenthesis ii right parenthesis comma space BC over HC space equals space AD over FG space equals space fraction numerator straight V subscript 1 straight t over denominator HC end fraction space equals space fraction numerator straight V subscript 2 straight t over denominator FG end fraction space space FG over straight V subscript 2 space equals space fraction numerator BC space minus space BH over denominator straight V subscript 1 end fraction FG over straight V subscript 2 space equals space fraction numerator BC space minus space EF over denominator straight V subscript 1 end fraction space open square brackets BH space equals space EF close square brackets FG over straight V subscript 2 space space equals space BC over straight V subscript 1 space minus space EF over straight V subscript 1 FG over straight V subscript 2 space equals space EF over straight V subscript 1 space equals space BC over straight V subscript 1 space Existence space of space wavefront space is space confirmed. space In space increment space ABC comma space sin space straight i space equals space BC over AC space space space space space space... space left parenthesis iii right parenthesis In space increment space ADC comma sin space straight r space equals space AD over AC space space space space space... space left parenthesis iv right parenthesis Dividing space equation space left parenthesis iii right parenthesis space by space Eq. space left parenthesis iv right parenthesis fraction numerator sin space straight i over denominator sin space straight r end fraction space equals space BC over AD fraction numerator sin space straight i over denominator sin space straight r end fraction space equals space fraction numerator straight V subscript 1 straight t over denominator straight V subscript 2 straight t end fraction straight mu subscript 2 space equals space fraction numerator sin space straight i over denominator sin space straight r end fraction space equals straight V subscript 1 over straight V subscript 2 Thus space Snells apostrophe straight s space law space is space confirmed. space Hence space proved. space$