NATURE OF LIGHT

Newton’s corpuscular theory of light
Newton’s corpuscular theory of light is based on the following points 1. Light consists of very tiny particles known as “corpuscular”. 2. These corpuscles on emission from the source of light travel in straight line with high velocity 3. When these particles enter the eyes, they produce image of the object or sensation of vision. 4. Corpuscles of different colours have different sizes.
Huygen’s wave theory of light
In 1679, Christian Huygens proposed the wave theory of light. According to huygen’s wave theory: 1. Each point in a source of light sends out waves in all directions in hypothetical medium called "ETHER". 2. Light is a form of energy 3. Light travels in the form of waves. 4. A medium is necessary for the propagation of waves & the whole space is filled with an imaginary medium called Ether 5. Light waves have very short wave length
Quantum theory of light
Quantum theory was put forward by MAX-PLANCK in 1905. According to quantum theory “Energy radiated or absorbed can not have any fractional value. This energy must be an integral multiple of a fixed quantity of energy. This quantity is called “QUANTUM” OR Energy released or absorbed is always in the form of packets of energy or bundles of energy. These packets of energy are known as QUANTA or PHOTONS

SIMPLE PENDULUM

SIMPLE PENDULUM
	simple pendulum consists of a heavy mass particle suspended by a light, flexible and in-extensible string.
	MOTION OF THE BOB OF SIMPLE PENDULUM
	The motion of the bob of simple pendulum simple harmonic motion if it is given small displacement. In order to prove this fact consider a simple pendulum having a bob of mass 'm' and the length of pendulum is 'l'. Assuming that the mass of the string os pendulum is negligible. When the pendulum is at rest at position 'A', the only force acting is its weight and tension in the string. When it is displaced from its mean position to another new position say 'B' and released, it vibrates to and fro around its mean position.
	Suppose that at this instant the bob is at point 'B' as shown below :
	FORCES ACTING ON THE BOB
	1. Weight of the bob (W) acting vertically downward. 2. Tension in the string (T) acting along the string.
	The weight of the bob can be resolved into two rectangular components:
	a. Wcosq along the string. b. Wsinq perpendicular to string.
	Since there is no motion along the string, therefore, the component Wcosq must balance tension (T) i.e.                                                                      Wcosq = T
	This shows that only Wsinq is the net force which is responsible for the acceleration in the bob of pendulum.
	According to Newton's second law of motion Wsinq will be equal to m x a
	i.e.                                                                      Wsinq = m a
	Since Wsinq is towards the mean position, therefore, it must have a negative sign. i.e.                                                                     m a = -  Wsinq
	But W = mg
	m a = -  mgsinq
	a = -  gsinq
	In our assumption q is very small because displacement is small, in this condition we can take sinq = q
	Hence                                                                     a = -  gq ----------- (1)
	If x be the linear displacement of the bob from its mean position, then from figure, the length of arc AB is nearly equal to x
	From elementary geometry we know that:
	Where s= x, r = l
	Putting the value of q in equation (1)
	As the acceleration of the bob of simple pendulum is directly proportional to displacement and is directed towards the mean position, therefore the motion of the bob is simple harmonic when it is given a small displacement

TORQUE - CENTER OF GRAVITY

TORQUE - CENTER OF GRAVITY

Torque
The torque or moment of force can be define as
“ The tendency of a force to produce rotation in a body about an axis is called torque or moment of force."
The turning effect of a force depends upon two factors:    The magnitude of force (F)    Moment arm (r)    The torque about any axis is given by the product of force and moment arm
Torque = force x moment arm OR
Positive torque:    If a body rotates about its axis in anti clockwise direction, then the torque is taken positive .
Negative torque:    If the body rotates in the clockwise direction, then the torque is taken as negative .
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Center of gravity
The center of a body is that point in the body through which the resultant forces due to the earth’s    attraction posses and through which the whole weight of the body always acts.    OR    Center of gravity of a body is a point where total weight of the body is concentrated.    Every body posses a center of gravity and this is irrespective of the body. Its is not necessary that the    center of gravity should be within the body, but it may also be situated in space out side the body.    Example: center of gravity of a ring is at the center, which is in the space.    Center of gravity of different objects:    Rectangle    Center of gravity of a rectangular is at the point of intersection of its diagonals    Circle    Center of gravity of a circle is at its center.    Square    Center of gravity of square is at the point of intersection of its diagonals.    Regular bar    The center of gravity of a regular bar is at its geometrical center.     Triangle    The center of gravity of a triangle is at the point of intersection of its medians.     Cylinder    The center of gravity of a cylinder is at the axis of cylinder.