consider the following ??. what is light electric field... is the space around an electric charge,...
TRANSCRIPT
Consider the Following ??
What is Light
Electric Field...•Is the space around an electric charge, it does not have mass.
It is not matter
• It exerts a force on other electrically charged objects and is able to do work.
Electric field is
…energy
Magnetic Field…• surrounds magnetic
materials, it also does not have mass and also is not matter
• it is detected by the force it exerts on other magnetic materials
Magnetic field also is
energy
Do electric and magnetic fields interact?
• Static (not moving) Electric field does not exert force on magnetic materials
• Static (not moving) Magnetic field does not exert force of electrically charged objects.
»However….
Electric and Magnetic Interaction
• Moving or alternating (changing in strength) electric field will generate magnetic field. ie an electro magnet
Similarly,
• Moving or alternating (changing in strength) magnetic field will generate electric field.
Electromagnetic Wave
• Electric and magnetic fields may pass energy one to another without any wire
• This energy moves ahead (propagates) in a straight line at 300,000 km/s
• Electromagnetic wave is a transfer of energy by constant interaction between electric and magnetic fields.
Like in Transversal Water Waves,
• Particles of medium (a toy duck and water itself) do not move ahead, but swinging up and down
• Energy moves ahead(Watch animation of surface wave now)
Direction of
propagation
amplitude
In Longitudinal Waves (like Sound),
• Particles of medium (air molecules) do not move ahead, they swing back and forth
• Energy moves ahead(Watch animation of sound wave now)
• Medium (e.g. air) gets more compressed. This repeats again and again. The compression moves away from the source.
• water wave: energy moves ahead by vibrating water
• Sound wave: energy moves ahead by vibrating air
• Wave in a rope: rope twists to send energy impulse ahead
• Electromagnetic wave does not need medium. It can travel through vacuum, a space free of matter.
Mechanical Waves vs Electromagnetic Wave
•Watch animation now
Speed for all wavelength in vacuum is :
V = 300,000 km/s
Short or long, all the waves will make same distance in one second
Shorter waves will get chance to oscillate more times during that time
shorter waves have higher frequency
Shorter waves with higher frequency are more energetic
Wavelength(λ): max to max distance
Frequency(f): # of cycles per second
Lower frequencies (long waves)
Wavelength measured in:
km (kilometres)
metres
cm (centimetres)
mm (milimetres)
Continues over!
Highest frequencies (short waves)
Wavelength measured in:
nm (nanometres)
1nm = 10-9m
size of protein
nm (nanometres)
or Å (Angstrom)
1 Å = 10-10m
size of water molecule
Even more ouch! - more energy
The other end of spectrum
What’s in the Middle of the Electromagnetic Spectrum?
Wavelength measured in:
mm (milimetres), 10-3m
µm (micrometres),10-6m,
Size of bacteria
nm (nanometres), 10-9m
Size of one cell
All the wavelength / frequency ranges:
ROY G BIV
FrequencyEnergy
• Light is an electromagnetic radiation
• It is pure energy moving ahead, it does not need medium to propagate
• It moves always in the straight lines within same (while in the same) medium
• All wavelengths (colours) move at the same speed in vacuum, c = 3.00*108m/s
Photons: how light is produced• - Electrons within atoms can move
from one energy level to another.
- Electrons move to higher levels when gain energy; they release energy when move to lower levels.
- Light is the energy released by electrons when they change energy level in atoms.
- For that, energy has to be input first.
• Which electromagnetic wave is shorter: gamma ray or radio wave?
• Gamma ray
• Which wave is more frequent: gamma ray or radio wave?
• Gamma wave
• Which one is more energetic?• Gamma ray
Light does act as a wave
It can be cut by a narrow slot (polarization)
Light diffracts: spreads around when exits narrow gate
Light does act as a wave
When waves overlap, intensities of two waves add up (interferention)