Chapter 11: Electromagnetic Waves

Question 1

What are the properties of electromagnetic waves?

Answer 1

• Electromagnetic (EM) waves are non-mechanical as they do not require a material medium to travel.
• All EM waves travel at 3 x 10^8 m/s in vacuum (Their speed in air is approximately the same as their speed in vacuum)
• EM waves are caused by the oscillation of electrical chargers (e.g. electrons)
• EM waves consists of electric field (E) and magentic field (B) perpendicular to one another and oscillating in phase (at the same frequency)
• EM waves are transverse waves as the electric field and magnetic field oscillate perpendicularly to the direction of wave travel
• EM waves obey the wave equation, v = fλ
• EM waves obey the laws of reflection and refraction
• EM waves transfer energy through oscillating electric field and magnetic field.
• The higher the frequency (or. smaller the wavelength) of the waves, the greater the energy (Energy ∝ f)
• The greater the amplitude of the oscillating electric field and= oscillating magnetic field, the greater the energy. (Energy ∝ E² or B²)

Question 2

What is the order from shortest and longest wavelength

Answer 2

• Gamma ray
• X-ray
• Ultraviolet
• Visible light
• Infra-red waves
• Microwaves
• Radio waves

Question 3

What are the properties of gamma rays?

Answer 3

• High penetrating power They can pass through all materials due to their high energy. THey can be slowed down or shielded by lead.
• High ionising power. They have enough energy to break chemical bonds or remove electrons from atoms and molecules. Hence, they can cause damage to DNA which can lead to growth of cancerous cells

Question 4

What are uses of gamma rays?

Answer 4

• Used to sterilise medical equipment
• Used to sterilise food (irradiated food).
• Used in radiotherapy to kill cancer cells. (Disadvantage: Gamma rays may cause damage to living cells and cause cancer)

Question 4

What are the properties of X-rays?

Answer 4

• High penetration power. X-rays can penetrate through materials except for lead.
• High ionising power. They have enough energy to break chemical bonds or remove electrons from atoms and molecules. Hence, they can cause damage to DNA which can lead to growth of cancerous cells.

Question 5

What are the uses of X-rays?

Answer 5

• Used in capturing image for medical purposes (e.g. fractured bones). X-rays can pass through muscles and are blcoked byh bones
• Used in capturing image of contents in containers (e.g. X-ray scanner at the airports)

Question 6

What are the uses of ultraviolet (UV) radiation?

Answer 6

• UV A are used in sunbeds for tanning purpose.
• Strong UV B and UV C radiation are used in germicidal lamps for sterilisation in hospitals
• UV has florescence property on some chemicals. Most bank noes have invisible ink that when UV waves are shone on, the fluorescent marking appear.
• In fluorescence lamps, UV radiation is produced when electrons bombard mercury atoms. When the UV radiation falls onto the fluorescent coating on the inside surface of the lamp, the coating emits white, visible light.

Question 7

What are the properties of UV radiation?

Answer 7

• The Sun is a source of the full spectrum of ultraviolet (UV) radiation, which is commonly subdivided into UV-A (longest wavelength), UV-B and UV-C (shortest wavelength)
• UV radiation has high ionising power.

Question 8

What are the uses of visible light?

Answer 8

• Use in optical-fibre communications. Light signals travel through the transparent fibre from the source to the reciever.
• Used in laser surgery. A laser is an intense beam of monchromatic (waves of only one single wavelength) and coherent (waves are in phrase with one another) light.

Question 8

What are the properties of visible light?

Answer 8

• The Sun and burning fuesl emit visible light.
• The human eye is most sensitive to the visible light

Question 9

What are the properties of infared radiation?

Answer 9

• These waves (sometimes referred to as ‘heat waves’) produce heating effect
• The sun is the main source of infared waves
• Infared radiation from the Sun is absorbed by greenhouse gases such as CO2 and CH4. Increased level of greenhouse gases in the atmosphere leads to global warming.
• The human body emits infrared radiation but infrared cameras can detect it.

Question 10

What are the uses of infrared radiation?

Answer 10

• The ear thermometer is used to measure the temperature of the body by measuring the amount of infrared radiation.
• Used in infraredremote controllers aere used to control a variety of electrical devices such as the TV.
• Infrared travels down fibre optic cables more efficiently than visible lught, and so most fibre optic communication systems use infrared
• Used in security cameras to detect intruders or for night vision

Question 10

What are the uses of infrared radiation

Answer 10

• The ear thermometer is used to measure the temperature of the body by measuring the amount of infrared radiation
• Used in infrared remote controllers are used to control a variety of electrical devices such as the TV.
• Infrared travels down fibre optic cables more efficiently than visible light, and so most fibre optic communication systems use infrared.
• Used in security cameras to detect intruders or for night vision.

Question 10

What are the properties of microwaves?

Answer 10

• Used in microwave oven. The microwaves cause the water molecules in food to vibrate more vigoruously (greater kinetic energy.) The water and food then increase in temperature.
• Satellite televisions use microwaves to receive televison programmes via satellites in space. Microwaves can pass through the charged layer (called ionosphere) in the upper atmosphere.
• Wifi, rader, mobile phones, satellite communications

Question 11

What are the properties of radio waves?

Answer 11

• Radio waves can travel long distances and are able to go around obstructions due to their longer wavelengths.
• Radio waves are emitted and recived by anntennae.

Question 12

What are the uses of radio waves?

Answer 12

• Used in radio broadcasting
• Used in telephone transmission, television, radios and navigation system (GPS). Note than radio waves cannot be used for staellite communiation as they get reflected by the ionosphere in the upper atmosphere.
• MRI uses a magnetic field and radio waves to detect hydrogen nuclei of water molecules in an internal organ in order to produce images of the organ on the computer.