Monochromatic light
Light of a single frequency
Normal
A line perpendicular to the mirror surface where the reflection occurs
Laws of reflection
- Angle of incidence = angle of reflection
2. The incident ray, the reflected ray and the normal all lie in the same plane
Refraction
The bending of light when it passes from one medium to another
Laws of refraction
- Snell’s Law - refractive index is the ratio of sin i / sin r
- The incident ray, refracted ray and the normal all lie in the same plane
Critical angle
The angle of incidence in the denser medium when the angle of refraction in the less dense medium is 90°
Characteristics of image formed by a plane mirror
- Same size
- Laterally inverted
- Upright
- Virtual (cannot be projected onto a screen)
- Object and image have the same distance from mirror
Uses of optical fibres
- Used in telecommunications as optical fibres can carry enormous amounts of information at very high speeds in light pulses trapped inside them
- Used in endoscopes that allow surgeons to examine patients’ internal organs
As the object distance decreases…
As the object distance decreases, the image distance increases and the image size increases
Features of EM waves
- Can travel through a vacuum / do not need a medium
- Travel through a vacuum at the speed of light
- Are transverse waves
- Transfer energy
Uses of radio waves
- Radio stations
- Televisions
- Cordless phone signals
- Airplane communications
Uses of microwaves
- Mobile phones
- Satellite television
- Heating effect used in microwave ovens
- Police radar
Uses of infra-red waves
- TV remote controllers
- Intruder alarms
- Electrical appliances, eg. grills, radiant heaters
Uses of ultraviolet rays
- Kill bacteria
2. In black light to find blood and saliva
Uses of X-rays
- See broken bones
2. In airport security systems to look for hidden objects
Uses of gamma rays
- Treat cancer
- Sterilise medical equipment
- Check for leaks in pipes
- Smoke detectors
Safety issues of microwaves
Microwaves can cause internal heating of body tissues
Safety issues of infra-red radiation
Infra-red radiation can cause skin burns
Safety issues of ultraviolet rays
Overexposure to ultraviolet rays increases the risk of skin cancer
Safety issues of X-rays and gamma rays
X-rays and gamma rays are ionising radiation that can cause mutations leading to cancer
*ionising radiation strips electrons from atoms in their path so the atoms become ions
