1. DIFFRACTION
NURUL FADHILAH ALIAS
MRSM KUALA KLAWANG

2. Solar glory at
the steam from hot
springs.
A glory is an optical
phenomenon produced
by light backscattered
(a combination of
diffraction, reflection an
d refraction) towards its
source by a cloud of
uniformly sized water
droplets.

3. Waves tend to
curve round
the edges of
the barriers.

4. 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!!!

5. 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

6. 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

7. Small vs. Large OBSTACLE
SMALL
LARGE
• Effect of diffraction is obvious
• Effect of diffraction is not so obvious

8. 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?

9. DIFFRACTION OF LIGHT WAVES
Diffraction pattern of a
PIN HOLE EXP.
Bright
and
dark
fringes
Diffraction pattern of a
SINGLE SLIT PLATE
Bright
and
dark
fringes
The light spread after
spreading the pin hole
The light
spread after
passing the slit

11. 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!

12. Experiment 1
Effect of the size of slit on diffraction pattern
Conclusion:
The smaller the size of the slit, the greater the effect of diffraction.

13. Experiment 2
Effect 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.)

14. Experiment 3
Effect 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.

15. 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.