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Across 2. an effect expressible as a quantity that repeatedly and regularly fluctuates above and below some mean value, as the pressure of a sound wave or the voltage of an alternating current 6. a unit of energy in the form of light 7. an intervening substance, as air, through which a force acts or an effect is produced 10. fundamental concept of quantum theory holding that energy sometimes behaves like particles and sometimes behaves like waves, so that descriptions of energy as one or the other are inadequate 11. The sensation of a frequency 13. the change that you notice in a sound, light, etc. as you get closer to it or farther from it 14. the interference of two waves of equal frequency and opposite phase, resulting in their cancellation where the negative displacement of one always coincides with the positive displacement of the other

Down 1. the interference of two or more waves of equal frequency and phase, resulting in their mutual reinforcement and producing a single amplitude equal to the sum of the amplitudes of the individual waves. 3. these points are the opposite of nodes 4. increased amplitude of oscillation of a mechanical system when it is subjected to vibration from another source at or near its own natural frequency 5. the change in direction that occurs when a wave of energy such as light passes from one medium to another of a different density 8. the bending or spreading out of waves, e.g. of sound or light, as they pass 9. when two or more waves come together 12. a point along a standing wave where the wave has minimum amplitude.