waves_3 (2)

Created by a disturbance.Waves carry energy from one

place to another

Waves (Def.) – A wave is a disturbance that transfers energy.

Medium – Substance or region through which a wave is transmitted.

Speed of Waves – Depends on the properties of the medium.

Water wave. The particles of water oscillate up and down from the equilibrium position. The wave is travelling from left to right. P is going down, Q is at the maximum displacement, and R is going up.

Energy is transferred without transfer of matter e.g.???????

Displacement Wavelength Period (deduce an expression for the

speed) Intensity (relation to amplitude A) Frequency Phase- Fraction of cycle the particle has

passed through relative to a given starting point.

© 2000 Microsoft Clip Gallery

Phase difference Φ-is the fraction of a cycle by which one leads or lags behind the other.

Path difference- between two waves is the number of cycles difference there is in the distance they have to travel.

Sine and Cosine are out of phase by /2 radians.

A ripple tank dipper makes 8 water waves in a time of 2s. When it is just about to make the 9th wave, the first wave has travelled 48 cm from the dipper.

(a) What is the frequency of the waves? (b) What is the wavelength of the

waves? (c) What is the wave speed?

(a) Period of each wave = 2/8 = 0.25 s () f = 1/0.25 = 4 Hz

(b) wavelength = 48/8 = 6 cm

(c) speed v = f = 4 Hz 6 cm = 24 cm/s ()

Solution

On the picture below, draw a second wave that is lagging the first wave by 90o, i.e. it’s behind the first wave. Draw another wave that is radians out of phase. Is it leading or lagging?

Both longitudinal and transverse waves can be represented by a displacement-distance graph. If we take a snapshot of a wave at any instant, we see:

Transverse

Longitudinal

Notice that we obtain the same graph.

Can’t differentiate by looking!!!

Speed in Vacuum 300,000 km/sec i.e. 3 x 108 m/s

Speed in Other Materials Slower in Air, Water, Glass

Energy is perpendicular to direction of motion

Moving photon creates electric & magnetic field Light has BOTH Electric & Magnetic fields at right angles!


Visible Spectrum – Light we can see Roy G. Biv – Acronym for Red, Orange, Yellow, Green, Blue, Indigo, & Violet.

Largest to Smallest Wavelength.

Invisible Spectrum Radio Waves

Def. – Longest wavelength & lowest frequency.

Uses – Radio & T.V. broadcasting.


Modulation - variation of amplitude or frequency when waves are broadcast AM – amplitude modulation

Carries audio for T.V. Broadcasts Longer wavelength so can bend around hills

FM – frequency modulation Carries video for T.V. Broadcasts


Invisible Spectrum (Cont.) Infrared Rays

Def – Light rays with longer wavelength than red light.

Uses: Cooking, Medicine, T.V. remote controls

Invisible spectrum (cont.). Ultraviolet rays.

Def. – EM waves with frequencies slightly higher than visible light

Uses: food processing & hospitals to kill germs’ cells

Helps your body use vitamin D.

Invisible Spectrum (Cont.) X-Rays

Def. - EM waves that are shorter than UV rays.

Uses: Medicine – Bones absorb x-rays; soft tissue does not.

Lead absorbs X-rays.

Invisible spectrum (cont.) Gamma rays

Def. Highest frequency EM waves; Shortest wavelength. They come from outer space.

Uses: cancer treatment.

TYPE USES DANGERSGAMMA

X-RAYS

UV

VISIBLE

INFRA RED

MICROWAVES

RADIO / TV RAYS

TREATING CANCER/STERILISATION

MEDICAL

SUN BEDS

PHOTOGRAPHY

REMOTE CONTROL /HEAT TRANSFER

SATELLITES / PHONES

COMMUNICATIONS

MUTATION OF CELLS

MUTATION OF CELLS

SKIN CANCER

NONE (IF NOT OVERLY EXPOSED OR IF YOU STARE AT THE SUN

SUN BURNS

VERY FEW

VERY FEW

waves_3 (2)

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