An ideal 100-V dc battery is applied across a series combination of four resistors having resistances of 20 Ω, 40 Ω, 60 Ω, and 80 Ω. What is the potential difference across the 40-Ω resistor?

1. do the particles in the medium material move in the same direction of the wave or at opposite direction to the wave? explain your answer. 2. by inputting more energy into the wave, i.e a large shake of the spring, which wave property also increases? 3. are there forces of friction acting while a wave is passing through a medium?