2.1 Light

1. Preparation - Chapter 2.1a, Chapter 2.1b, Chapter 2.1c, Chapter 2.1d, Chapter 2.1e 

2. Participation - Assignment P.55 Q10-16 except 14

3. Presentation - Blackboard, Student's Work

4. Possession
   > Energy is emitted when an excited atom demote to lower energy level.  Light is emitted if the energy change falls between a certain range.
   > Gas discharge lamp which includes fluorescent tube lamp (FTL), compact fluorescent lamp CFL, High-density discharge (HID) lamp - their working mechanism
   > FTL: electrodes accelerate electrons ionises the tube,  mercury atoms are excited, then  UV light emission followed by fluorescence by phosphor coating

1. Preparation - Chapter 2.1b

2. Possession
   > Incandescent lamp/filament lamp: filament, joule heating, demote to emit a range of light, but much are infra-red, that explains its low efficacy.
   > halogen lamp: filled with Bromine or iodine to reduce evaporation of filament.

1. Preparation - Chapter 2.1c

2. Possession
   > Light Emitting Diode (LED): current may only flow from p-type to n-type, electrons and holes diffuse to each other and forms an E-field from n- to p-type semiconductor.
   > Applied E-field from p- to n-type semiconductor may drive a current, by giving excess energy to the charge carriers, and they may emit light when oppositely charged carriers combined.
   >   LED works only when p-type semiconductor is connected to a higher potential.

1. Preparation - Chapter 2.1d

2. Possession> Power rating is input power (consumed by the appliance)> Brightness is subjective.  Our eyes are more sensitive to 555 nm that other wavelengths of light.> luminous flux is a measure of visible power, the unit is lumen (lm). A 555 nm light source of 1W output produces 683 lm.> Read the relative sensitivity graph and fill in the blanks on the left!> light bulbs, read the labels!
   > illuminance measures the visible power per unit area as perceived at the certain point from a light source.  It is the luminance flux per unit area, falling through the surface perpendicularly.
   > ...

1. Preparation - Chapter 2.1e 

2. Possession
   > ...