DIFFRACTIONNURUL FADHILAH ALIAS

MRSM KUALA KLAWANG

Solar glory at the steam from hot springs.

A glory is an optical phenomenon produced by light backscattered (a combination of diffraction, reflection and refraction) towards its source by a cloud of uniformly sized water droplets.

Waves tend to curve round the edges of the barriers.

DIFFRACTION…DEF. :

the spreading out of waves when they move through a gap or around an obstacle.

CHARACTERISTICS: the direction of propagation and shape of the

waves change Wavelength? Frequency? and Speed?

remains the

same!!!

DIFFRACTION OF WATER WAVES

SMALL SLIT

• The waves are more circular and originates from the small slit

• The effect of diffraction is obvious

LARGE SLIT

• The waves are bent only at the edges

• The effect of diffraction is not so obvious

If the gap is bigger than the wavelength,

i ) the waves in the centre go through the gap unchanged

ii) the waves at the edges are diffracted

Small vs. Large OBSTACLE

SMALL

• Effect of diffraction is obvious

LARGE

• Effect of diffraction is not so obvious

If the barrier is bigger that the wavelength, a large shadow area is formed behind the barrier. the diffraction pattern of the waves is less obvious.

The pattern of light diffraction is not easily seen because it wavelength is small ( x 10 -7 m).

AMPLITUDE of waves AFTER diffraction is SMALLER!

WHY?

DIFFRACTION OF LIGHT WAVES

Diffraction pattern of a PIN HOLE EXP.

Diffraction pattern of a SINGLE SLIT PLATE

The light spread after passing the slit

The light spread after spreading the pin hole

Bright and dark fringesBright

and dark fringes

Diffraction In Light Waves Will Occur When

1. Width of the slit or pin hole

• Must be COMPARABLE to that of wavelength of the light waves.

2. Light Source

• The light source must be MONOCHROMATIC

• i.e. one wavelength only!

Experiment 1Effect of the size of slit on diffraction pattern

Conclusion:The smaller the size of the slit, the greater the effect of diffraction.

Experiment 2Effect of the colour of light  on diffraction pattern

Conclusion:The longer the wavelength, the greater the effect of diffraction.(Red light has longer wavelength while purple light has shortest wavelength.)

Experiment 3Effect of the distance of the screen from the slit  on diffraction pattern

Conclusion:The further the screen from the slit, the further the distance between bright bands formed on the screen .

DIFFRACTION OF SOUND WAVES• Sound waves diffract around corners

• Audible sound waves have wavelengths in the range of 1.5 cm to about 15 metres…

• Hence, sound waves in the range of the width of a doorway (around 1-2 metres) will diffract in the room.