Light, Lenses and the Electromagnetic Spectrum

Electromagnetic waves are transverse and travel at the same speed in a vacuum. From low to high frequency the spectrum runs radio, microwave, infrared, visible, ultraviolet, X-ray and gamma. Higher frequency means shorter wavelength at fixed speed. Uses depend on absorption, penetration and interaction with matter: infrared supports thermal imaging, microwaves communications or heating, and X-rays imaging. Ionising radiation can damage cells, so evaluate the particular dose and application.

Reflection obeys equal incidence and reflection angles measured to the normal. At refraction, a speed change can alter the ray direction; entering a slower region bends toward the normal for ordinary positive-index materials. A colour depends on which visible wavelengths are emitted, reflected or transmitted. A red filter transmits red light rather than painting every incoming wavelength red. Use ray arrows to show travel direction.

A converging lens can form a real image from an object beyond its focal point, while an object inside that point gives a virtual magnified image. A diverging lens gives a virtual upright diminished image for an ordinary real object. Draw principal rays consistently: a ray parallel to the axis refracts through, or appears to come from, a focal point. Magnification is image height divided by object height. State whether an image is real or virtual as well as its size and orientation.

Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.