Chapter 5: Infrared, Ultraviolet, X-rays and Spectroscopes

Chapter 5: Infrared, Ultraviolet, X-rays and Spectroscopes

1. Infrared Rays

• Properties:

• Emit strong heat, easily absorbed by objects and converted into heat energy.

• Affect photographic film, used for night-time infrared photography.

• Cause some chemical reactions.

• Can be modulated like high-frequency electromagnetic waves, used to make remote controls.

• Cause the photoelectric effect in some semiconductors.

• Applications:

• Used in remote control devices, drying equipment, microwave ovens, medical equipment, etc.

2. Ultraviolet Rays

• Sources:

• Objects with temperatures above 2000°C (e.g., electric arcs, the surface of the Sun).

• Properties:

• Affect photographic film, stimulate the fluorescence of some substances.

• Stimulate chemical reactions.

• Ionize air and some gases.

• Biological effects, such as tanning and skin cancer.

• Strongly absorbed by water and glass, but can pass through quartz.

• Applications:

• Sterilization, treatment, finding cracks on surfaces.

3. X-rays

• Properties:

• Strong penetrating power, the shorter the wavelength, the greater the penetrating power.

• Blacken photographic film, used for X-ray imaging in medicine.

• Cause fluorescence in some substances.

• Ionize air.

• Biological effects, destroy cells, used for cancer treatment.

• Applications:

• Finding defects inside objects, inspecting baggage at airports, studying the structure of solids.

4. Spectroscopes

• Tool:

• Analyzes complex light beams into different monochromatic components.

• Structure:

• Collimator tube, prism, dark chamber/imaging chamber.

• Conditions for obtaining an absorption line spectrum:

• The temperature of the absorber must be lower than the temperature of the source of the continuous spectrum.

• Reversal of spectral lines:

• At a specific temperature, an object only absorbs the radiation it can emit, and vice versa, it only emits radiation it can absorb.