During your study in a junior school you were told that light travels in a straight line. But now you know that light travels as a wave and it can bend around objects. In optical region light has a wavelength of about half a micrometre. If it encounters an obstacle of about this size, it may bend around it and can be seen on the other side. however, if the obstacle is much larger, light will not be able to bend to that extent and will not be seen on other side. This is a general property of waves and can be seen in sound waves too. the sound wave of our spech has a wavelength of about 50 cm-1m. if it meets an obstacle of the size of a few metres, it bends around it and reaches points behind the obstacle. but when it comes, across a larger obstacle of a few hundred metres, such as a hillock, most of it is reflected back and is heard as an echo. Q. Under what condition can you observe diffraction of light ?