Waves (electromag spec + light)

• Waves transfer energy through vibrations without transferring matter.
• Speed of a wave is the distance travelled by a wave in 1 second.
• Period is the time taken to generate one complete wave.
• Frequency is the number of complete waves generated per second.
• Amplitude is the maximum displacement of the wave from the rest position.
• Wavelength is the distance between two successive crests/troughs.
• Wavefront is the imaginary line joining all peaks or identical points on a wave.
• A transverse wave travels in a direction perpendicular to the direction of vibration. Eg surface water waves, electromagnetic waves
• A longitudinal wave travels in a direction parallel to the direction of vibration. Eg sound waves
• speed (m/s) = frequency (Hz) * wavelength (m)

  v=fλ
• frequency (Hz) = 1 / time period (s)

  f = 1/T
• speed (m/s) = wavelength (m) / time period (s)

  v=λ/T
• Qn: Describe how sound waves are transmitted through a medium.

  When the source of a sound wave vibrates, the surrounding particles are disturbed and vibrates in a direction parallel to the direction of the sound waves.

  The vibrations are passed on from one particle to the

  next in a series of alternate regions of compressions

  and rarefactions, transmitting the sound waves

  through the medium.
• Sound will travel fastest in solids, since solid particles are closest together, and vibrations from the source will be passed on from particle to particle the fastest.

  Sound will travel slowest in gases, since gaseous particles are furthest apart, and vibrations from the source will be passed on from particle to particle the slowest.
• Sound cannot be transmitted in a vacuum due to the absence of particles in a vacuum.
• Total distance travelled by sound wave= speed * time = v * t
• The louder the sound, the higher the amplitude of the sound wave.

  The higher the frequency, the higher the pitch of the sound wave.
• All electromagnetic waves are transverse waves.
• All electromagnetic waves travel at a speed of 3 x 10^8 m/s in vacuo (plural for vacuum)
• Lowest frequency to highest frequency

  Radio waves, Microwave, Infrared rays, Visible Light rays (ROYGBIV), Ultraviolet rays, X-rays, Gamma rays

  [Ronald Mcdoanld Is Very Ugly Xcept Gary]
• Radio waves application is radio and television communication, astronomy and RFID tags; wireless networks; mobile phone networks; GPS systems; police radios; radiocontrolled toys
• Microwave application is mobile (cell) phones, microwave oven and satellite television; satellite communications
• Infra-red ray application is infrared remote controllers, intruder alarms and thermal imaging; weather forecasting; infra-red tracking missiles; infra-red heaters
• Visible light ray application is photography, optical fibres in medicine and telecommunications; lighting; endoscope
• Ultraviolet ray application is sunbeds, bank note authentication and disinfecting water; sterilisation of medical equipment
• X-ray application is medical radiology, security screening and industrial defect detection
• Gamma ray application is sterilising food, detection of cancer and its treatment
• Effect of absorbing electro magnetic waves

  Heating Effect:

  1. Infrared heating -> Fires and hot bodies emit infra-red radiation. Our skin absorbs the infra-red rays, making us feel warm.
  2. Microwaves heating -> Microwaves are of a non-ionizing character. However, microwaves, being more penetrative, can cause more severe burns to the skin, especially when skin has high water content.
• Effect of absorbing electro magnetic waves:

  Ionisation Effect:

  • UV rays, X-ray, Gamma ray can cause breakdown of DNA, and ionization of molecules and atoms in living matter. The mutation of these cells and atoms can lead to formation of cancerous cells
• The normal is a line perpendicular to the surface.
• Light is a form of energy.

  Light travels at 3 x 10^8 m/s in vacuum/air.

  Light travels in straight lines.
• Laws of reflection

  First Law:

  The incident ray, reflected ray and the normal all lie in the same plane.

  Second Law:

  The angle of incidence is equal to the angle of reflection.
• Refractive index of a medium is defined as the ratio of the speed of light in vacuum to the speed of light in the medium
• Critical angle is the angle of incidence in the optically denser medium for which the angle of refraction in the optically less dense medium is 90°.
• Total internal reflection occurs when light travels from a denser to a less dense medium and the angle of incidence in the denser medium is greater than the critical angle. The incident ray in the denser medium is reflected within the medium completely.
• n = sin i / sin r
• n = speed of light in air or vacuum / speed of light in medium

  n = c / v
• n = 1 / sin c

  For finding critical angle of a medium
• n = real depth / apparent depth
• Conditions for TIR:

  1. Light ray is travelling from denser optical medium to a less dense optical medium.
  2. Angle of incidence in the denser medium is greater than the critical angle of the medium.