# Consider the Following ??

## Presentation on theme: "Consider the Following ??"— Presentation 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,
amplitude Direction of propagation 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)

In Longitudinal Waves (like Sound),
Medium (e.g. air) gets more compressed. This repeats again and again. The compression moves away from the source. Particles of medium (air molecules) do not move ahead, they swing back and forth Energy moves ahead (Watch animation of sound wave now)

Mechanical Waves vs Electromagnetic Wave
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. Watch animation now

Wavelength(λ): max to max distance
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 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)
The other end of spectrum Wavelength measured in: nm (nanometres) 1nm = 10-9m size of protein or Å (Angstrom) 1 Å = 10-10m size of water molecule Even more ouch! - more energy

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:
Energy ROY G BIV

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?
Which wave is more frequent: gamma ray or radio wave? Gamma wave Which one is more energetic?

Light does act as a wave It can be cut by a narrow slot (polarization)

Light does act as a wave Light diffracts: spreads around when exits narrow gate When waves overlap, intensities of two waves add up (interferention)