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.

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)