Physics

CBSE Class 12

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2.

The carrier wave is given by C (*t*) = 2sin (8π*t*) Volt.

The modulating signal is a square wave as shown. Find modulation index.

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For any charge configuration, equipotential surface through a point is normal to the electric field. Justify.

Work done (*W*) in moving a test charge along an equipotential surface is zero.

Work done is given by,

F is the electric force and s is the magnitude of displacement.

For non-zero displacement, this is possible only when cos is equal to 0.

= 90°

Thus, the force acting on the point charge is perpendicular to the equipotential surface.

Electric field lines give us the direction of the electric force on a charge.

Thus, for any charge configuration, an equipotential surface through a point is normal to the electric field.

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4.

Two spherical bobs, one metallic and the other of glass, of the same size are allowed to fall freely from the same height above the ground. Which of the two would reach earlier and why?

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6.

Write the expression, in a vector form, for the Lorentz magnetic force due to a charge moving with velocity in a magnetic field B. What is the direction of the magnetic force?

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7.

Out of the two magnetic materials, 'A' has relative permeability slightly greater than unity while 'B' has less than unity. Identify the nature of the materials 'A' and 'B'. Will their susceptibilities be positive or negative?

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8.

Given a uniform electric field E =5 ×10^{3 }N/C, find the flux of this field through a square of 10 cm on a side whose plane is parallel to the y-z plane. What would be the flux through the same square if the plane makes a 30° angle with the x-axis?

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10.

A capacitor 'C', a variable resistor 'R' and a bulb 'B' are connected in series to the ac mains in circuit as shown. The bulb glows with some brightness. How will the glow of the bulb change if (i) a dielectric slab is introduced between the plates of the capacitor, keeping resistance R to be the same; (ii) the resistance R is increased keeping the same capacitance?

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