P4: Waves

Transverse

Oscillations that are perpendicular to the direction of energy transfer. Particles move from side to side. The amplitude goes up an down while the wave moves from left to right.

Longitudinal

Oscillations that are parallel to the direction of energy transfer. Particles move back and forth. Some parts of the wave are closer together (compression) and some are further apart (rarefaction)

angle of incidence=

angle of reflection

Equation for refractive index

n=c/v

n= refractive index

c= velocity of light in a vacuum (3.0\*10^8)

v= velocity of light in a substance

\

Snells law

n1sinθ1=n2sinθ2

n1= incidence index

n2=refracted index

θ1= incident angle

θ2=refracted angle

refractive index

the measure of the **bending** of the **refracted angle** when it goes from **one medium to another**

optical fibers + examples

Optical fibres allow TIR because each time light bounces inside the fibre, the angle of incidence is greater than the critical angle. The glass must be on high purity as well.

**Used in telecommunication, internet, messages, endoscopes,**

Total internal reflection

When the angle of incidence is greater than the critical angle, this results in no light being lost

Real image + examples

Real images are images that can be projected onto another medium

Virtual image + examples

Images that cannot be projected onto another medium

order of electromagnetic spectrum in frequency (l to h)

radio - micro - infra - visible- UV- xray - gamma

Electromagnetic waves in a vacuum and air

Electromagnetic waves can also travel in vacuums like space as well as air, this is because electromagnetic waves do not need a medium.

Radio waves (radio and tv communications)

• television broadcasts, mobile phones

• transverse

• safe because of long wavelengths

microwaves ( satellite tv and telephones)

• transverse

• satellite tv and telephones

• high exposure can cause burns

Infra-red waves (electric applainces, security, remote controllers for tvs)

• transverse

• Security, remotes, night-vision

• long exposure can cause eye damage

X-rays (medicine)

• transverse

• medicine

• radiation sickness, DNA mutations

wavefront

Where all the points of the crest join

 v = f λ

wave speed=frequency\*wavelength

waves peed: m/s

frequency: Hz

wavelength:m

examples of longitudinal waves

Sound waves

examples of transverse waves

all electromagnetic waves (radio, microwave)

Crest and trough

Crest: the highest point of the wave

trough: the lowest point of the wave

Wavelength

The distance of one peak to the next

Amplitude

The distance between the crest and the center of the wave

What happens when a wave passes through a gap?

The wavefronts spread

Waves

Waves transfer energy from one place to another without transferring matter, it can be observed as sound and light. When they travel from one place to another, they vibrate and/or oscillate.

frequency

How many oscillations of a wave per time period

Describing words for ray diagrams

inverted (upside down)

Enlarged (bigger)

Diminished (smaller)

real or virtual

upright

UV ray dangers

Skin cancer, premature aging.

Converging lenses

Thicker in the middle, when rays pass through a converging lens, they converge at the focal point.

The distance between the center of the lens to the focal point is called the focal length

Diverging lenses

Thinner in the middle