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Q18. State and explain Biot -Savart's law.

              (OR)

        A fine insulated wire 15.7 m. long is used to make a coil of radius 5 cm, find the magnitude of  magnetic induction in air, at the centre of the coil, when the current of 0.2A is sent through it.


Q19. Define :

      (i) Magnetic dipole

      (ii) Magnetic length

      (iii) Magnetic moment

Q20. State properties of electric lines of force.

Q21. State law of conservation of momentum. Give any two examples.

 

Dear Student,
Q20.

Properties of Electric Lines of Force are:

1)The tangent to the line of force at a point gives the direction of Electric field intensity at that point.

2) Electric lines of forces never cross each other. This point can be cleared easily through a figure.

Let us suppose that two lines intersect at a point. So draw tangents to that point along the lines of force. You will see that their will be two directions of the electric field intensity at a single point, which is not possible.electrostatic 2.26

3)Electric Lines of Force start from positive charges and end at negative charges.

4)They do not form any closed loop.

Q21.

Conservation of momentum states that the momentum of the body remains conserved if no external force is applied on it. 

The state of rest or motion is not disturbed if external force is not applied on it. If external force is applied on the body the state will change with change in its momentum. 

Suppose a body is moving in a straight line with a constant speed. The body will continue its motion and the momentum of the body will remain conserved until and unless some external force acts on it. The change in momentum can be observed only when external force acts on the body. Internal force never brings change in the momentum of the body.

Examples of conservation of momentum: 

Rocket – Gas system Initially when the rocket is at rest the momentum of the system is zero. When rocket takes off it throws gas in opposite direction to its motion. The magnitude of the velocity of the gas in downward direction is equal to the magnitude of the velocity of rocket in the upward direction. The direction of velocity is in opposite direction therefore the net momentum again comes out to be zero and hence the conservation of momentum. 

Bullet fired from the gun Here also initially when no bullet is fired the net momentum of the bullet-gun system has zero momentum. When bullet is fired the magnitude of the velocity of the bullet in forward direction is equal to the magnitude of the velocity of gun in the backward direction. The direction of velocity is in opposite direction therefore the net momentum again comes out to be zero and hence the conservation of momentum. This is the reason why recoil of gun is observed.

for remaining queries ask in different thread.
Regards,

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