EM Waves & General Wave basics

Waves transfer energy in the direction…

that they are travelling

amplitude means

the maximum displacement of a point on the wave from its undisturbed position.

Wavelength means

distance between the same point on 2 adjacent waves

Frequency means

and is measured in

number of complete waves passing a certain point per second. 1  Hz = 1 wave / second

The period of a wave means

the amount of time it takes for a full cycle of the wave to pass a point.

Formula for period of a wave

t = 1/f

t is period in seconds

f is frequency in Hz

Transverse waves have __ vibrations

the oscillations are __ to the direction of energy transfer

perpendicular

perpendicular

Longitudinal waves have __ vibrations

the oscillations are __ to the direction of energy transfer

parallel

parallel

Complete the longitudinal diagram

The important equation:

wavespeed (define this too)

wavelength

frequency

with units!

3 wave experiments using the equation

1. Sound: a speaker attached to signal generator. 2 microphones attached to an oscilloscope. move microphones in relation to each other until the 2 waves line up on oscilloscope. measure distance between microphones for wavelength

2. Ripple tank

3. String: signal generator attached to vibration transducer attached to string with pulley with masses on at end. measure nodes

EM Radiation:

As you go down from Radio to Gamma,

frequency __

and wavelength __

(increase/decrease)

frequency up

wavelength down

Radio waves uses

long range communication

short wave signals reflect off the ionosphere, so bounce around the earth and off its atmosphere

long wave signals bend around the earth

TV and FM radio would be very short wavelength radio waves, because to get signal you must be in direct sight of transmitter. Signal doesn't bend or travel far through buildings.

2  uses of microwaves

1. satellite comms. Micro is best for passing easily through earth’s watery atmosphere

2  . microwave ovens, where water molecules absorb microwaves which have penetrated a few cm into the food. they then quickly spread this absorbed energy to the rest of the food.

Infrared is used for

monitoring temperature.

It is given off by everything, more if the object is hot, less if cold. IR cameras can show the IR being given off, red for more, green for less.

used by police and nature ppl

Fibre optic cables can be used for

they use which type of wave?

using visible light to transmit data

UV uses

1. suntanning

2. fluorescence: Chemicals absorb UV and emit visible light. Used in hi-vis jackets, security pens, detecting forgery

X- Rays and Gamma Rays in medicine: talk about the uses

X-rays pass easily through flesh, but not bones, so we can see bones on the image clearly because they absorb the waves.

X and gamma can be targeted at cancer cells to kill all cells in the area, but it’s risky.

Risk: radiation dose is measured in

Sieverts

Sv

higher frequency waves usually more dangerous