Which of the following is the best explanation of why it is difficult to discriminate the color of an object at night?

a. cones come in three types, each sensitive to different wavelengths of light.
b. the foveae are densely packed with cones.
c. at night, the amount of light entering the eye is insufficient to stimulate the cone cells but is sufficient to stimulate the rod cells.
d. as many as 100 cones may converge on one ganglion cell.

When using two-wire cable to feed a 240-v appliance that does not require a neutral wire, you should a. mark both ends of the white wire green. b. use the cable as is. c. use only the black wire. d. mark both ends and any exposed area of the white wire black.

Electric field of the earth. the earth has a net electric charge that causes a field at points near its surface equal to 150 n> c and directed in toward the center of the earth. (a) what magnitude and sign of charge would a 60-kg human have to acquire to overcome his or her weight by the force exerted by the earth’s electric field? (b) what would be the force of repulsion between two people each with the charge calculated in part (a) and separated by a distance of 100 m? is use of the earth’s electric field a feasible means of flight? why or why not?

How does an observation about an object differ from an inference about that object