Laws of reflection of light---- angle of incidence = angle of reflection. Incident ray, normal, reflected ray lies on the same plane.

Refraction of light--- refraction is the bending of light when it travels from one material into another. When light passes from air into a more dense medium such as water, glass of plastic, it slows down.

Law of refraction of light—Incident ray, refracted ray and normal all lie in same plane

SinI / Sin R = refractive index.

Refractive index = Ci / Cr (Ci = speed of light in incident ray. Cr= spend of light in refracted ray.)

The critical angle is when the angle of refraction is equal to 90 degrees. Beyond the critical angle, the ray is entirely reflected inside the block. This is called total internal reflection. The critical angle is related to the refractive index of the material. N= 1/ sin C

The greater the refractive index, the smaller the critical angle.

Optic fibre --- light travels through a glass fibre by total internal reflection.   It helps to see inside the human body, transmit signals for phone calls and cable TV.

Advantages:  

1.visible light—high frequency which carries lots of information

2.It doesn’t heat up----- less energy loss

3.Little interference.

Multipath dispersion--- a single pulse which enters the fibre at one end will be spread out by the time it reaches the other end. Rays which travel along the center of the fibre follow the shortest path and reach the end first; rays which zig-zag along the fibre follow a longer path and reach the end later.

This problem can be overcome by using narrow fibres and fibres which are more dense in the centre.

An object vibrates when it moves backwards and forwards about a fixed point. When a string of a guitar vibrates, a wave is formed. Example of vibration: air moving from a loudspeaker, water particles in a sea water.

Waves show reflection and refraction in ripple tank.

Refraction: water waves slow down when they enter shallower water. If the waves approach the boundary between deep and shallow water at an angle, the effect is for the waves to change direction. Their wavelength decreases, the waves become closer together. Their frequency remains the same.

Reflection: wave front will reflect back when it hits any barriers.

The number of complete wave per second is the frequency. (hertz)

The distance from any point on a wave to the next exactly similar point (crest to crest) is the wavelength. (m)

The distance of a point on the wave from it undisturbed position is called the displacement. (m)

The maximum displacement of any point on the wave from it undisturbed position is called amplitude.(m)

The time taken for one complete vibration is called the period (S) of the motion.

T = 1/f.

There is a phase difference when the points on waves vibrate out of phase with each other.

Wave energy is the energy that is transmitted by the wave. Each particle vibrates: as it does so, it pushes its neighbor, transferring energy to it. Then that particle pushes its neighbor, which pushes its neighbor. In this way, energy is transmitted from one particle to the next, to the next and so on down the line.

The intensity of a wave tells us how fast it transfers energy from place to place. Eg, the energy transferred by the sun is 1000J per second on each square meter on the earth surface.

The speed which energy is transmitted by a wave is know as the wave speed.

Wave speed = wavelength / period = (wavelength / 1/ f) = wavelength * Frequency

Waves move through a material is called progressive waves so energy transfers due to a progressive wave.

The oscillator is connected to one end of the spring. When it is switched on, the end of the spring is moved up and down and a series of longitudinal pulses travels up the spring and reflects from the top

.

Waggle the end of the slinky spring from side to side. The segments of the spring move from side to side as the wave travels along the spring.

Graphical representations of transverse and longitudinal waves:

Polarisation---- Transverse waves can be polarized but longitudinal waves can not.

Light is a transverse wave. Light, which is unpolarised, has vibrations in all directions at right angles to the direction in which it is travelling. If the light passes through a piece of Polaroid, it becomes polarised which means only vibrations in one direction can get through. A second piece of Polaroid placed at 90 degrees to the fist will stop this light.

Usage: Polaroid sunglasses

These reduce glare by selecting one polarization of light waves only so the amount of unpolarised light reaching the eyes is reduced. Light reflected from a road tends to be polarised horizontally and the Polaroid in sunglasses is arranged to cut out this light.

A Polaroid filter can help in photography by cutting out light reflected form the surface of the water, it allows us to see down to the seabed.

The Frequency, wavelength and amplitude of a sound wave can be very clearly shown using an oscilloscope and a microphone. The microphone is connected to the oscilloscope’s Y-input. Short- form------- C.R.O

To work out the frequency, I need to know the time base--- the time interval represented by each cm horizontally. T= 1/f

The oscilloscope describes the shape of the sound waves and this property is know as their quality or timbre.

The shapes of waves from different instructment are different but they have same frequency.

White noise is a sound that contains a large number of frequencies.

The principle of superposition--- the resultant effect of two waves which meet at a point simply by adding up the displacements at the point along their length is called the principle of superposition of waves.

Explain: two loudspeakers are connected to a single signal generator. They each produce sound waves of the same wavelength. If u walk around in the space in front of the loudspeakers, you will obverse the resultant effect. At some points, the sound is louder than for a single speaker, at some points, the sound is much quieter.

At some points, the 2 waves arrive at a point in phase with on another and with equal amplitude, constructive interference will happen.

At some points, 2 waves arrive out of phase with one another. (one goes up and one goes down) they cancel each other out. This effect is know as destructive interference.

Direct the light from a laser through two slits. Where the light falls on the screen, a series of equally spaced dots of light are seen. These are referred to as interference fringes and they are points where light waves from the two slits are arriving in phase with each other-----. Constructive interference. The dark regions in between are the result of destructive interference.

If one slit is covered, the pattern of interference fringes disappear, a broad band of light appears across the screen.

Interference of microwaves---- by moving the probe around, it’s possible to detect regions of high intensity and low intensity.

Interference of water waves ---- two dippers in the ripple tank vibrate. Each dipper acts as a source of circular ripples spreading outwards. Where these sets of ripples overlap, we observe an interference pattern. Another way to observe interference in a ripple tank is to use plane waves passing through two gaps in a barrier.

Coherence---- two waves with the same frequency and a constant phase difference between them. In order to observe interference, wee need two coherent sources of waves with same frequency. If they were not coherent sources, the interference pattern would be constantly changing, far too fast for out eyes to detect. Use splits in front a single source or two-linked laser.

Property of wave: interference, reflection, refraction, diffraction and polarization.

When two rays of waves are arriving in phase, a bright fringe is shown on the screen, this is the interference pattern. Where there is a dark fringe, their path lengths differ by a whole number of wavelengths plus half a wavelength. When there is constructive interference, the path difference is equal the whole number of wavelengths. When there is destructive interference, the path difference is equal to the whole number of wavelengths plus half a wavelength.

Determining wavelength----- wavelength = (a * x ) / D

--- a = the distance between the slits, x = distance between the fringes , D = distance between the slits and the screen.

`Diffraction--- when wave fronts are restricted by a barrier with a gap, the waves bend at the corner and spread out.

A ripple tank can be used to show diffraction; plane waves are generated using a vibrating bar and they then barrier at a gap in a barrier. Where the ripples strike the barrier , they are reflected back. Where they arrive at the gap, they pass through and spread out into the space beyond. It’s this spreading out of waves as thy travel through a gap is called diffraction.

The extent to which ripples are diffracted depends on the width of the gap.

The wider the gap, the smaller the effect on diffraction. As the gap becomes narrower, the effect becomes more pronounced. It is greatest when the width of the gap is equal to the wavelength of the wave.

Standing wave---- when a wave and its reflection traveling in opposite directions interference. A long rope is laid on the floor and is fixed it’s end firmly. Wave the other end from side to side so that waves travel along and reflect off the fixed end. there are points which remain motionless on the standing wave are called nodes. A node is a position where the amplitude of the stationary wave is zero. The points on either side, which are oscillating, back and forth are called antinode.

Node--- result to the destructive interference….. Antinode—result to constructive interference.

Stretched strings: A string is attached at one end to a vibration generator, driven by a signal generator. The other end hangs over a pulley and weights maintain the tension in the string. When the vibrations are switched on, the string vibrates with small amplitude. As the frequency is increased, it’s possible to observe one loop, two loops, three loops and more. By measuring the distance between nodes, it’s possible to find the wavelength of the waves on the string. (melde’s experiment)

When u hold a vibrating tuning fork above the open end, the air column may be forced to vibrate and the note of the tuning fork sounds increasingly louder. If the length of the air column is right adjusted, a very loud note will be heard. This must be the node. First node = ¼ wavelength.

For a stringed instrument such as guitar, the two ends of a string are fixed so nodes must be established at these points. When the string is plucked half-way along its length, it vibrates with an antinode at its mid point.

In a wind instrument, by changing the length of the air column, the note can be changed.

The string or air column is forced to vibrate. It has its own natural frequency of vibration and the note of this frequency therefore sounds loudest. This is called the resonance. The air column experiment is called a resonance tube.

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