Write the expression for Lorentz magnetic force on a particle of

Subject

Physics

Class

CBSE Class 12

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 Multiple Choice QuestionsShort Answer Type

1.

Define electric dipole moment. Write its S.I. unit. 

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2.

Where on the surface of Earth is the angle of dip 90°? 

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3.

A hollow metal sphere of radius 5 cm is charged such that the potential on its surface is 10 V. What is the potential at the centre of the sphere?

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4.

How are radio waves produced?

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5.

Two bar magnets are quickly moved towards a metallic loop connected across a capacitor ‘C’ as shown in the figure. Predict the polarity of the capacitor. 


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6.

A thin straight infinitely long conducting wire having charge density straight lambda is enclosed by a cylindrical surface of radius r and length l, its axis coinciding with the length of the wire. Find the expression for the electric flux through the surface of the cylinder. 

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7.

Plot a graph showing the variation of coulomb force (F) versus , where r is the distance between the two charges of each pair of charges: (1 C, 2 C) and (2 C – 3 C). Interpret the graphs obtained. 

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8.

Write the expression for Lorentz magnetic force on a particle of charge ‘q’ moving with velocity v in a magnetic field B  . Show that no work is done by this force on the charged particle.

OR 

A steady current (I1) flows through a long straight wire. Another wire carrying steady current (I2) in the same direction is kept close and parallel to the first wire. Show with the help of a diagram how the magnetic field due to the current I1 exerts a magnetic force on the second wire. Write the expression for this force.


Lorentz magnetic force is given by, 

Therefore, work done is, 


As, 

So, Work done, W = 0

                                                            OR

Consider two long straight conductors PQ and RS placed parallel to each other carrying currents I1 and I2 respectively. Conductors experience an attractive force when the conductors move in the same direction while, repulsive force is experienced by the conductors when currents move in opposite direction.

PQ and RS which are placed at a distance r, carry currents I1 and I2 in the same direction.

Suppose, a current element ‘ab’ of length  of wire RS.

The magnetic field produced by current-carrying conductor PQ at the location of other wire RS,


So, total force on the conductor of length L is given by, 

Force acting per unit length of conductor is given by,  

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9.

What are eddy currents? Write any two applications of eddy currents.

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10.

In the given circuit, assuming point A to be at zero potential, use Kirchhoff’s rules to determine the potential at point B.

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