Convex and concave lenses • Images formed by a convex lens • Images formed by a concave lens • Magnification • The lens formula Heat • Measuring temperature • The Celsius temperature scale • Internal energy and energy transfer • Heat transfer processes • Power and measurement of energy transferred • Heat capacity and specific heat capacity Formulas • Magnification • Lens formula • Relationship between length of a liquid column and temperature of a liquid-in-glass thermometer • Power • Heat capacity of a body • Specific heat capacity of a body

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Lenses are transparent optical devices that refract light to form images. There are two main types of lenses. Convex lenses are thicker in the middle and converge light rays to a focal point. Concave lenses are thinner in the middle and diverge light rays outward. Convex lenses form different types of images depending on the object's position. When an object is placed beyond the focal point, the lens forms a real, inverted image on the opposite side. Light rays from the object converge after passing through the lens. When the object is within the focal point, a virtual, upright, and magnified image is formed on the same side as the object. Concave lenses always form virtual, upright, and diminished images regardless of object position. Light rays from the object diverge after passing through the lens. The virtual image appears to come from the intersection of the backward extensions of the diverged rays. This image is always on the same side as the object, upright, and smaller than the original object. Two important formulas describe lens behavior. Magnification equals image height divided by object height, or image distance divided by object distance. The lens formula relates focal length to object and image distances: one over f equals one over u plus one over v. These formulas help calculate unknown quantities when working with lenses in optical systems. Heat and temperature are fundamental concepts in thermal physics. Temperature measures the average kinetic energy of particles, while heat is energy transfer between objects at different temperatures. Internal energy is the total energy of all particles. Key formulas include Q equals m c delta T for heat capacity, and P equals E over t for power. Thermometers measure temperature using thermal expansion of liquids.