Select the three hypotheses. Grass prevents erosion when planted on a hillside.

Eating sweets may affect weight gain in children.

Brand X battery maintains a charge longer than brand Y.

Hummingbirds are aggressive animals.

A child will catch a cold if she plays in the rain.

If a plant receives fertilizer, it will grow at a faster rate.

Why do scientists believe that light is made of streams of particles? scientists believe that light is made of streams of particles because only the presence of photons can explain phenomena observed during experiments on the photoelectric effect. these observations include only some frequencies of light causing the ejection of electrons, no time gap existing between light striking a metal and electrons being ejected, and intensity having no effect on the kinetic energy of the ejected electrons.

When many atoms are split in a chain reaction, a large explosion occurs. this is an example of what type of energy conservation

Follow these directions and answer the questions. 1. set up the ripple tank as in previous investigations. 2. bend the rubber tube to form a "concave mirror" and place in the ripple tank. the water level must be below the top of the hose. 3. generate a few straight pulses with the dowel and observe the reflected waves. do the waves focus (come together) upon reflection? can you locate the place where the waves meet? 4. touch the water surface where the waves converged. what happens to the reflected wave? 5. move your finger twice that distance from the hose (2f = c of c, center of the curvature) and touch the water again. does the image (the reflected wave) appear in the same location (c of c)? you may have to experiment before you find the exact location. sometimes it is hard to visualize with the ripple tank because the waves move so quickly. likewise, it is impossible to "see" light waves because they have such small wavelengths and move at the speed of light. however, both are examples of transverse waves and behave in the same way when a parallel wave fronts hit a curved surface.