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ISC Class 12 Physics Solved Question Paper 2008

Short Answer Type

21. Obtain an expression for the electric potential at a point which is at a distance r from the point charge Q.

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22. Find the equivalent capacitance of the following circuit between the junctions A and B; given C₁ = C₂ = C₃ = C₄= 10μF and C₅ = 5,μF.

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23. A galvanometer with a coil of resistance 100 Cl and a scale having 100 divisions has a current sensitivity of 25 μ A / division.'How will you convert it into an ammeter of range 0 to 5A ?

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24. The emf ‘E’ of a thermocouple varies with the temperature θ (in degree C) of the hot junction (cold junction at 0°C) as E = 15 q 0.05 q^2.
Determine the neutral temperature.

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25. Using either deflection magnetometer or vibration magnetometer, explain how will you compare magnetic moments of two given bar magnets.

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26. Two very long straight parallel conductors carrying currents I₁ and I₂ in vacuum are separated by a distance ‘a’. Write an expression for the force experienced per unit length by one wire due to the current flowing through the other wire and hence define the fundamental unit of current, i.e., an ampere.

Force between two parallel current carrying conductors

Let parallel conductors are I and II. I₁, current is flowing through conductor I and I₂through II.

The force experienced per unit length by the current carrying conductor I due to the magnetic field produced by the conductor II. Magnetic field at point P due to current I₂ is given by,

According to right hand thumb rule, the direction of the magnetic field B₂ at point P is perpendicular to the plane of paper and in inward direction.

Now the conductor I carrying current I₁ lies in the magnetic filed B₂ produced by the conductor I₂.

Since, F = B I l

Hence,

F = B₂ x (l₁ x I) =

Force, F =

Definition of Ampere:

Let I₁ = I₂ = 1 A and a = 1 m

Then from above equation, we have

One ampere is the current which when flowing through each of the two parallel conductors of infinite length and placed in free space at a distance of 1 metre apart, produces between them a force of 2 x 10 ^-7newton per metre of their lengths.

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27. When the primary of a transformer is connected to a 120 V AC mains, the current in the primary is 18.5 mA. Find the voltage across the secondary when it delivers 1.5 mA current through it, assuming the transformer to be an ideal one. State any one type of energy loss in a transformer.

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28. Draw a simple ray diagram showing the formation of a primary rainbow.

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29. Using Huygen’s Principle, prove the laws of refraction of light.

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30. The figure below shows the positions of the first bright fringes B₁, and B₂ on either side of the central bright fringe O in Young’s double slit experiment. Find the wavelength of monochromatic light used.