At dawn and dusk, large amount of blue and violet light(shorter wavelength) has been scattered so, the light that is recieved by an observer is mostly of a longer wavelength and therefore appears to be red.
SinceECu2+/CuECu2+/Cuhas a greater positive value thanEH+/HEH+/H, the reaction that is feasible at the cathode is
Cu2+(aq)+2eCu(s)
A negative of a vector represents the direction opposite to the reference direction. It means that the magnitude of two vectors are same but they are opposite in direction.
For example, if A and B are two vectors that have equal magnitude but opposite in direction, then vector A is negative of vector B.
In the air, there's nothing holding the body of the helicopter still - so the rotor blades spin one direction, but the torque applied to spin the rotors tries to spin the body of the helicopter in the opposite direction. The little rotor on the tail helps keep the body of the helicopter pointed in the same direction.
