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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.

Using Deflection Galvanometer:

We can use deflection galvanometer by setting it in end-on position or broad side-on position,

(i) By setting the magnetometer in end-on position : When the deflection magnetometer is placed so that the two arms of the magnetometer and 0°-0° line lie along east-west line, the magnetometer is said to be placed in end-on position.

So the horizontal component of earth’s magnetic field (B_H) is perpendicular to the magnetic field (B) produced by the bar magnet as shown in figure.

Magnetic moment can be compared by using deflection method or null method.

Consider two equal bar magnets A and B having magnetic moments M₁ and M₂ respectively.

Let l be length of the each magnet. Place magnet A on the arm of the magnetometer lengthwise r at a distance effect of an r from the centre of the magnetometer.

Let B₁ be magnetic field due to magnet at the centre of the magnetometer box.

If the magnetic needle ns of the magnetometer box deflect at an angle θ, then,

B₁ = B_Htanθ₁...(1)

Since, magnetic needle lies on the axial line of the magnet,

Place magnet B in place of magnet A at the same distance r from the centre of the magnetometer, magnetic needle deflects at an angle 0₂, then as obtained in case of magnet A, we have

By calculating θ₁ and θ₂ the ratio M_l/M₂ can be calculated.

ii)

By setting the magnetometer in broad side-on position :

When the deflection magnetometer is placed, so that the arms of the magnetomer and 90°-90° line lie along the N-S magnetometer is said to be placed in broad side-on position.

The horizontal component of earth’s magnetic field to magnetic’s magnetic field.

Let M₁and M₂ magnetic moments of magnets A and B.

2l be length of each magnet.

Place magnet A on the arm of magnetometer breadthwise at a distance r from the centre of the box as shown in figure.

Let B₁be the magnetic field due to the centre of the magnetometer box. If the magnetic needle ns deflects through angle θ₁, then

B = B_Htan θ₁ ...(6)

magnetic needle lies on the equitorial line of the magnet.

B₁ =

Using B₁ in equation, we have

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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.

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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.