Three practical uses of electromagnets would be
Light. The waves
Electric locks. The bolts that are used by the
coils
Cranes. The electric ones that are found in
scraps
Cars computers washing machines all use
Electromagnets . Even CD players DVDs
Players
<span>The velocity of light is by far the greatest in air. There is nothing in air to stop or impede the movement of light in air. When light travels in air it will not stop unless running into clouds, smoke, smoke, droplets, or impurities. Any other substance is harder for light to travel through.</span>
We see black colour in absence of light. Black colour absoorbs all the light, ( just opposite of white) and hence we do not see any colour. Black colour is also related to darkness.