Light generally travels in a straight line, following the path of a straight line in a homogeneous and isotropic medium. This behavior is known as rectilinear propagation. When light travels through a uniform medium, such as air or a vacuum, it typically moves in a straight path.
However, under certain circumstances, the path of light can be curved or bent. This phenomenon is called refraction and occurs when light passes through different mediums with varying optical densities, such as from air to water or from air to glass. The change in the speed of light as it enters a different medium causes it to bend.
Additionally, light can be influenced by gravitational fields, causing its path to curve. This phenomenon, known as gravitational lensing, occurs due to the bending of light by massive objects like stars or galaxies. Einstein's theory of general relativity predicts this curvature of light in the presence of strong gravitational fields.
In the context of peaks and troughs, it's important to note that light is an electromagnetic wave, and it exhibits wave-like properties, such as wavelength and frequency. These properties determine the peaks and troughs of the light wave. However, when considering the path of light in a given medium, it generally travels in a straight line, following the principles of geometric optics.