Pin Hole Experiment

1. Light is diffracted when passes through a pin hole.
2. Diffraction pattern is made up of alternate bright and dark ring..

Single Slit Experiment

1. Light is diffracted if it passes through a narrow slit.
2. Diffraction pattern is made up of the bright bands and dark bands of different width.
3. The central band is wider and brighter. The dark and bright bands of narrower width are alternatively observed on the left and right side of the central bight band.
4. Diffraction pattern obtained will be clearer if the size of the slit decreases.
5. Conditions for diffraction to take place are:
   1. Light source must be monochromatic. That is, the light must possess only one wavelength.
   2. Slit size must be small enough as compare with the wavelength of light.

Factors affecting the pattern of diffraction

The factors that will affect the distance between the bright bands are

1. Size of the slit
2. Colour of the light
3. Distance of the screen from the slit

 

1. Diffraction is the spreading of a wave when it travels through an opening or a small obstacle.

(Diffraction happen when waves pass through an opening)



(Diffraction happen when waves encounter an obstacle)


2. Characteristics of Diffracted Wave
   1. Wavelength does not change.
   2. Frequency does not change.
   3. Speed of diffracted does not change.
   4. The amplitude of the wave decreases after diffraction.

Factors Affecting the Magnitude of Diffraction

The magnitude of diffraction (or angle of diffraction) depends on

1. The wavelength
2. The size of the opening

Experiment 1

Shorter wavelength - The wave spreads to a smaller area

Longer wavelength - The wave spreads to a wider area

Conclusion:
Diffraction is affected by the wavelength. The longer the wavelength, the greater the effect of diffraction

Experiment 2

Bigger opening - The wave spreads to a smaller area

Smaller opening - The wave spreads to a wider area

 

1. When light travels one medium to another of differing density, its speed changes.
2. Speed of light is higher in a medium of less density as compare with one higher density. The change in velocity of light when it travels from one media to another of different density results in the refraction phenomenon.
3. As we have learned in form 4 chapter 5, light, the refraction of light obey the law of refraction, where $$\frac{\sin i}{\sin r}=\text{constant}$$

 

 

Speed of Water Waves

1. When straight waves pass from deep to shallow water, their
   1. wave-length becomes shorter
   2. speed decreases
   3. frequency remain unchanged
2. This can be illustrated by placing a piece of rectangular Perspex of suitable thickness in the tank to reduce the local water depth.
   
3. Figure below shows the wavefront diagram of the wave formed.
   
4. We can see that the wavelength above the Perspex is shallower.
5. The relationship between the speed and wavelength of the wave in deep and shallow region is given by the formula below.
6. 
7. v_d = speed of wave in deep region
   λ_d = speed of wave in deep region
   
   
   v_s = speed of wave in deep region
   λ_s = speed of wave in deep region

Refraction of Waves at a Boundary

1. Refraction is the change in direction of propagation when a wave moves from one medium to another medium.
2. It is caused by the change of the speed of the wave when moving from one medium to another.
3. For water waves, refraction occurs when the waves move from one region to another region of different depth.
4. If water waves pass through a shallow region of convex shape, the waves will be converged.
   
5. If water waves pass through a shallow region of concave shape, the waves will be diverged.
   

 

Experiment

Conclusion:

1. The angle of incidence, i is equal to the angle of reflection, r.
2. Sound waves obey the law of reflection. That is, the angle of incidence is equal to the angle of reflection.

 

1. The characteristic of reflection of light enables us to see objects. Objects that do not emit light are not seen in the dark. An object only is seen if light is incident on it a reflected back to our eyes

Experiment

2. The experiment of reflection of light wave shows that reflection of light wave obeys the law of reflection.

 

1. Reflection occurs when an incident wave hits a reflector and reflected back.
2. The direction of propagation of the wave changed when it is reflected.
3. The wavelength, frequency and speed of wave remain unchanged.
4. The amplitude of the wave may or may not change depend on the material of the reflector and the shape of the wavefront.

Reflection of Straight and Circular Wave

1. Reflection of waves obeys the law of reflection, that is
   1. The angle of incident is equal to the angle of reflection
   2. The incident wave, reflected wave and the normal lie on the same plane.
2. For reflection of circular wave, the distance of image from the reflector is equal to the distance of source of wave from the reflector.

(Reflection of Straight Plane Wave)

(Reflection of Circular Wave)

 

Phenomena of Waves

1. There are 4 phenomena of waves:
   1. Reflection
   2. Refraction
   3. Diffraction
   4. Interference
2. Diffraction and interference are unique phenomena. Only waves perform these phenomena.
   
   

 

Natural Frequency

The Natural frequency of an oscillating system is the frequency of the system when there is no external force or forces acting on it.

Damping

1. Damping is the decrease of amplitude of an oscillating system.
2. An oscillating system experiences damping when its energy is losing to the surrounding as heat energy.
3. Usually, the frequency of the system remain unchanged.

(Displacement-time graph of a damped oscillation)

(Amplitude-time graph of a damped oscillation)

Type of Damping

Damping can be divided into:

1. internal damping, where an oscillating system loses energy due to the extension and compression of the molecules in the system.
2. external damping, where an oscillating system loses energy to overcome frictional force or air resistance that act on it.

Force Oscillation

1. In a damped oscillation, external force must be applied to the system to enable the oscillation to go on continuously.
2. Oscillation with the help of external force or forces is called a force oscillation.

Resonance

In a force oscillation, if the frequency of the external force is equal to the natural frequency of the system, the system will oscillates with maximum amplitude, and this is named as resonance.

Examples of Resonance

1. Opera singer breaks a wine glass with her voice due to the effect of resonance.
2. Tacoma Narrow Bridge in USA collapsed in 1940 due to the effect of resonance.
3. A moving bus produces excessive noise at certain speed when the frequency of the engine equal to the natural frequency of the bus.

Bartons Pendulum

The characteristic of resonance can be demonstrated with a Barton’s pendulum system.


Observation:
1. When pendulum X oscillates, the other pendulums are forced to oscillate.
2. Pendulum D will oscillates with the largest amplitude.