A student stands in a school hallway. A wall separates a classroom from the student. The student in the hallway cannot see inside the classroom
but hears noises from within the classroom. Which of these best explains
why the student hears the noises but cannot see into the classroom?

What sort of waves exhibit the doppler effect?

If you put a helium-filled balloon in the refrigerator, what will happen?

Cells in the nervous system have a potential difference of 70 mv across the cell membrane separating the interior of the cell from the extracellular fluid. this potential difference is maintained by ion pumps that move charged ions across the membrane. is this an emf? select the correct answer and explanation. 1)no. the ion pumps cannot separate charges; thus, they cannot create a potential difference. 2)yes. the ion pumps cannot separate charges, but they still can create a potential difference. 3)yes. the ion pumps can actively separate charge; thus, they can create a potential difference. 4)no. the ion pumps can separate charges, but they cannot create a potential difference.