1. Electromagnetic wave is a periodically changing electromagnetic field propagating in space. Its propagation speed is the same as that of light in vacuum, and electromagnetic waves with different frequencies travel at the same speed in air, so information and energy can be transmitted in the process of propagation. 2. Modern communication mainly consists of satellite communication and optical fiber communication. Internet plays an increasingly important role in modern life, such as sending and receiving emails, online learning, online trading, shopping and holding video conferences. 3. Primary and secondary energy, renewable and non-renewable energy, conventional and new energy, clean energy and non-clean energy. 4. The ultra-high temperature and ultra-high pressure in the solar center of nuclear energy make the hydrogen nuclei in the sun interact, fuse and combine into helium nuclei. Application: hydrogen bomb. 5. Solar Energy All energy sources on the earth except nuclear energy, geothermal energy and tidal energy come from the sun. Three ways of using solar energy: solar water heater, solar cell and green plants. Are all applications of physics.