The electromagnetic spectrum is the distribution of electromagnetic waves according to their wavelength or frequency. It includes radio waves, microwaves, infrared radiation, visible light, ultraviolet rays, X-rays, and gamma rays. Radio waves have the longest wavelength in the spectrum, ranging from millimeters to kilometers. They are generated by accelerated electric charges and act as a carrier to transmit information. A microwave oven produces microwaves that heat up food. Heated surfaces emit infrared radiation. Remote controls use infrared radiation of wavelength around 0.9 micrometers. An incandescent bulb emits visible radiation with wavelengths ranging from 0.4 to 0.7 micrometers. Ultraviolet rays of wavelength around 0.35 micrometers are used to kill insects. Sources of high-frequency X-rays are intra-atomic transitions. X-rays of wavelength around 1 x 10-4 micrometers are used for scanning bones. Gamma rays are emitted during nuclear decay. Radiation therapy utilizes gamma rays.