Physics
A standing wave occurs when

Two waves overlap
The speed of the wave is zero or near zero
The amplitude of a wave exceeds its wavelength
A wave reflects upon itself

ANSWER DOWNLOAD EXAMIANS APP

Physics
Purpose of an optical filter is to

Refract light of different colours
Transmit or absorb light of different colours
Dispense light into component colours
Reflect lights of different colours

ANSWER DOWNLOAD EXAMIANS APP