CIE iGCSE Co-ordinated Sciences-P3.3 Electromagnetic spectrum- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-P3.3 Electromagnetic spectrum – Study Notes
CIE iGCSE Co-ordinated Sciences-P3.3 Electromagnetic spectrum – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
The Electromagnetic Spectrum
(a) Main Regions:
- The electromagnetic (EM) spectrum is the complete range of electromagnetic waves arranged in order of frequency or wavelength.
- All EM waves travel at the speed of light in a vacuum, \( c = 3.0 \times 10^8 \,\text{m/s} \).
- Main regions (in order of increasing frequency and decreasing wavelength):
- Radio waves
- Microwaves
- Infrared (IR)
- Visible light
- Ultraviolet (UV)
- X-rays
- Gamma rays
(b) Relationship Between Frequency and Wavelength:
- The wave equation links them: \( v = f \lambda \).
- Since \( v = c \) in a vacuum: \( c = f \lambda \).
- Thus:
- Higher frequency → shorter wavelength.
- Lower frequency → longer wavelength.
(c) Order of Regions:
| Region | Frequency Range | Wavelength Range | Typical Uses |
|---|---|---|---|
| Radio Waves | Lowest | Longest | Broadcasting, communication |
| Microwaves | Higher than radio | Shorter than radio | Cooking, radar, satellites |
| Infrared | Higher than microwaves | Shorter than microwaves | Remote controls, thermal imaging |
| Visible Light | Middle of spectrum | \( 400 \,\text{nm} \) – \( 700 \,\text{nm} \) | Human vision, photography |
| Ultraviolet | Higher than visible | Shorter than visible | Sterilisation, tanning, security |
| X-rays | Very high | Very short | Medical imaging, security scans |
| Gamma Rays | Highest | Shortest | Cancer treatment, sterilisation |
Example
A microwave has a frequency of \( 3.0 \times 10^9 \,\text{Hz} \). Calculate its wavelength in air.
▶️Answer/Explanation
Step (1) – Formula:
\( c = f \lambda \) → \( \lambda = \dfrac{c}{f} \).
Step (2) – Substitution:
\( \lambda = \dfrac{3.0 \times 10^8}{3.0 \times 10^9} \).
Step (3) – Solve:
\( \lambda = 0.10 \,\text{m} \).
Final Answer:
The wavelength of the microwave is \( 0.10 \,\text{m} \) (10 cm).
Speed of Electromagnetic Waves
- All electromagnetic (EM) waves travel at the same speed in a vacuum, regardless of their wavelength or frequency.
- This speed is known as the speed of light and is represented by the symbol \( c \).
(b) Numerical Value:
- The speed of electromagnetic waves in a vacuum is:
- \( c = 3.0 \times 10^8 \,\text{m/s} \)
- This value is the same for radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.
- In air, the speed is almost the same as in a vacuum (slightly less, but very close to \( c \)).
(c) Connection Between Speed, Frequency and Wavelength:
- The wave equation links the three quantities:
- \( v = f \lambda \), and in a vacuum or air, \( v = c \).
- Thus, if the frequency \( f \) increases, the wavelength \( \lambda \) decreases to keep \( c \) constant.
Example
Visible red light has a frequency of \( 4.5 \times 10^{14} \,\text{Hz} \). Calculate its wavelength in air.
▶️Answer/Explanation
Step (1) – Formula:
\( c = f \lambda \) → \( \lambda = \dfrac{c}{f} \).
Step (2) – Substitution:
\( \lambda = \dfrac{3.0 \times 10^8}{4.5 \times 10^{14}} \).
Step (3) – Solve:
\( \lambda = 6.7 \times 10^{-7} \,\text{m} \).
Final Answer:
The wavelength of red light is approximately \( 670 \,\text{nm} \), which is within the visible spectrum.
Applications of the Electromagnetic Spectrum
- Different regions of the electromagnetic (EM) spectrum have different properties (frequency, wavelength, energy).
- Because of this, each region has specific uses in daily life, medicine, communication, and industry.
- However, all EM waves travel at the same speed in a vacuum: \( 3.0 \times 10^8 \,\text{m/s} \).
(b) Applications by Region:
| Region of EM Spectrum | Applications |
|---|---|
| Radio Waves | Radio and TV transmission, Radar |
| Microwaves | Satellite TV, Mobile (cell) phones, Microwave ovens |
| Infrared (IR) | Remote controls, Thermal imaging, Night vision cameras |
| Visible Light | Human vision, Photography, Optical instruments |
| Ultraviolet (UV) | Detecting fake bank notes, Sterilisation of equipment |
| X-rays | Medical scanning (bones), Airport security scanners |
| Gamma Rays | Cancer detection and treatment, Sterilisation of medical equipment |
Example
A hospital uses X-rays for bone imaging. If the X-rays have a frequency of \( 3.0 \times 10^{18} \,\text{Hz} \), calculate their wavelength.
▶️Answer/Explanation
Step (1) – Formula:
\( c = f \lambda \) → \( \lambda = \dfrac{c}{f} \).
Step (2) – Substitution:
\( \lambda = \dfrac{3.0 \times 10^8}{3.0 \times 10^{18}} \).
Step (3) – Solve:
\( \lambda = 1.0 \times 10^{-10} \,\text{m} \).
Final Answer:
The wavelength of these X-rays is \( 1.0 \times 10^{-10} \,\text{m} \), which lies in the X-ray region of the spectrum.
Harmful Effects of Excessive Exposure to Electromagnetic Radiation
- Electromagnetic (EM) radiation carries energy that can interact with human tissue.
- The higher the frequency of the wave, the greater the energy, and the more harmful the radiation.
- Some forms of EM radiation can cause damage to cells and DNA, leading to health problems such as burns, cancer, or genetic mutations.
(b) Specific Harmful Effects:
| Region of EM Spectrum | Harmful Effects on Humans |
|---|---|
| Ultraviolet (UV) | $\bullet$ Damages surface skin cells $\bullet$ Causes sunburn $\bullet$ Increases risk of skin cancer $\bullet$ Can damage eyes (e.g., cataracts) |
| X rays | $\bullet$ Can penetrate the body and damage cells $\bullet$ Overexposure may cause mutations in DNA $\bullet$ May lead to cancers if used without shielding |
| Gamma Rays | $\bullet$ Very high$\bullet$energy radiation $\bullet$ Causes severe cell damage and mutations $\bullet$ Linked to cancers and radiation sickness $\bullet$ High doses can be fatal |
(c) Notes:
- Protective measures include: sunscreen (for UV), lead shielding (for X rays and gamma rays).
- Medical use of X rays and gamma rays is carefully controlled to ensure the benefits outweigh the risks.
Example
A worker in a nuclear facility is exposed to gamma radiation at a dose of \( 5 \,\text{mSv} \) (millisieverts). Explain why this is dangerous and how the risk can be reduced.
▶️Answer/Explanation
Step (1) – Identify the radiation:
Gamma rays have very high frequency and energy.
Step (2) – Harmful effect:
They can penetrate deeply, damage DNA, and cause mutations → possible cancer.
Step (3) – Safety measures:
Use thick lead or concrete shielding, reduce exposure time, and increase distance from the source.
Final Answer:
Gamma rays at \( 5 \,\text{mSv} \) can damage body cells and increase cancer risk. The danger can be reduced by shielding, limiting exposure, and maintaining distance.