Electromagnetic Waves and light

1. Quantum Model and Photons

  • Electrons occupy specific energy levels around the nucleus.

  • Higher energy levels = farther from the nucleus.

  • Lower energy levels = closer to the nucleus.

  • When an electron falls from a higher energy level to a lower one, it releases energy as a photon (light particle).

  • The greater the energy difference between levels, the higher the energy of the photon emitted.

Examples

  • Lasers

  • Fluorescent lights

  • Neon signs

2. Electromagnetic Radiation

Electromagnetic radiation is energy that travels as waves.

Examples:

  • Radio waves

  • Microwaves

  • Infrared radiation

  • Visible light

  • Ultraviolet radiation

  • X-rays

  • Gamma rays

All electromagnetic waves travel at the speed of light in a vacuum:

c=2.998×108 m/sc=2.998\times10^8\ \text{m/s}c=2.998×108 m/s

3. Wave Vocabulary

Crest

  • Highest point of a wave.

Amplitude

  • Distance from the rest position to the crest.

  • Indicates wave intensity.

Wavelength (λ)

  • Distance between two consecutive crests.

Frequency (f)

  • Number of wave cycles passing a point each second.

  • Measured in hertz (Hz).

Relationship

  • Short wavelength → High frequency

  • Long wavelength → Low frequency

4. Electromagnetic Spectrum

Region

Frequency

Wavelength

Radio Waves

Lowest

Longest

Microwaves

Higher

Shorter

Infrared

Higher

Shorter

Visible Light

Moderate

Moderate

Ultraviolet

High

Short

X-rays

Very High

Very Short

Gamma Rays

Highest

Shortest

Important Trend

As wavelength decreases:

  • Frequency increases

  • Energy increases

As wavelength increases:

  • Frequency decreases

  • Energy decreases

5. Radio Waves

Characteristics

  • Longest wavelengths

  • Lowest frequencies

  • Lowest energies

Uses

  • Radio broadcasting

  • Television signals

  • Cell phones

  • Cordless phones

  • Space communication

6. Production of Electromagnetic Waves

When electrons oscillate (move back and forth):

  1. Electric field (E) forms.

  2. Magnetic field (B) forms.

  3. Changing fields propagate outward as electromagnetic waves.

Receiving antennas detect these waves and convert them into electrical signals.

7. Energy of Electromagnetic Waves

Energy and frequency are directly proportional.

E=hfE=hfE=hf

Where:

  • E = energy (J)

  • h = Planck's constant = 6.626 × 10⁻³⁴ J·s

  • f = frequency (Hz)

Key Idea

Higher frequency → Higher energy

Examples:

  • Gamma rays = very high energy

  • Radio waves = very low energy

8. Sources of Light

A. Blackbody Radiation

A blackbody:

  • Absorbs all incoming radiation.

  • Re-emits radiation based on temperature.

Examples:

  • Sun

  • Burning coals

  • Incandescent bulbs

Temperature Effect

Higher temperature:

  • Greater intensity

  • Shorter wavelengths

  • Higher frequencies

B. Fluorescence

  • Substance absorbs light.

  • Almost immediately emits light of longer wavelength.

Examples:

  • Mercury vapor lamps

  • Fluorescent lights

C. Light Emitting Diodes (LEDs)

  • Emit light in specific energy bands.

  • Very energy efficient.

9. Visible Light

Visible light is the only portion of the electromagnetic spectrum detectable by human eyes.

Frequency Range

4.3 × 10¹⁴ Hz to 7.5 × 10¹⁴ Hz

Wavelength Range

400 nm – 700 nm

Color Order (ROYGBIV)

  1. Red

  2. Orange

  3. Yellow

  4. Green

  5. Blue

  6. Indigo

  7. Violet

Color Trends

Color

Wavelength

Frequency

Red

Longest

Lowest

Violet

Shortest

Highest

10. Infrared Radiation (IR)

Position

Between:

  • Microwaves

  • Visible red light

Wavelength Range

0.75 μm – 300 μm

Uses

  • Night vision goggles

  • Thermal imaging

  • Astronomy

Important Fact

Warm objects emit infrared radiation.

Examples:

  • Human bodies

  • Cars

  • Buildings

11. Ultraviolet Radiation (UV)

Position

Between:

  • Visible violet light

  • X-rays

Wavelength Range

10 nm – 400 nm

Types

Type

Energy

UVA

Lowest

UVB

Medium

UVC

Highest

Atmospheric Protection

  • Atmosphere blocks all UVC.

  • Atmosphere blocks most UVB.

  • About 95% of UV reaching Earth is UVA.

12. Effects of UV Radiation

Benefits

  • Helps body produce Vitamin D.

  • Assists calcium metabolism.

Risks

  • Sunburn

  • Skin damage

  • Premature aging

  • Skin cancer

Protection

Use sunscreen.

SPF = Sun Protection Factor

Higher SPF = Greater UV protection.

13. Incandescent Light Bulbs

  • Produce visible light through blackbody radiation.

  • Approximately 90% of emitted energy is infrared radiation.

  • Therefore, incandescent bulbs are inefficient.

Key Test Facts

  1. Electrons emit photons when dropping to lower energy levels.

  2. Electromagnetic waves travel at 2.998 × 10⁸ m/s in a vacuum.

  3. Wavelength and frequency are inversely related.

  4. Frequency and energy are directly related.

  5. Radio waves have the longest wavelengths.

  6. Gamma rays have the highest frequencies and energies.

  7. Red light has the longest visible wavelength.

  8. Violet light has the highest visible frequency.

  9. Infrared radiation is associated with heat.

  10. UVB helps produce Vitamin D.

  11. LEDs are more efficient than incandescent bulbs.

  12. Energy of electromagnetic radiation is given by E = hf.