Answer:
you need only one independent variable because if not, you wont know what factors have changed your experiment.
Explanation:
The photoelectric effect occurs when light shines on a metal. ... Light of any frequency will cause electrons to be emitted.
Salad, a bag of different colored pebbles or sand, etc
A)Constant pumping from the heart which provides adequate pressure necessary to move the blood through the arteries and veins
B)Gravitational force
No a molecule is 2 different atoms bond
