Physics - waves 1

Define: Wavelength

The distance of one entire oscillation of a wave

Define: Amplitude

The maximum displacement from the equilibrium/rest position

Define: Time period

The time it takes for one complete oscillation of a wave

What is the frequency formula?

f=1/T (frequency = 1/time period)

What are the units for frequency?

Hertz (Hz)

What is the formula for wave speed?

v = fλ (velocity = frequencyXwavelength)

Define: transverse wave

A wave where the oscillations are perpendicular to the direction of energy transfer

Define: longitudinal wave

A wave where the oscillations are parallel to the direction of energy transfer

Define: frequency

The number of waves produced by a source per second/ the number of waves passing a point per second

Define: wavelength

The distance travelled by a wave in a given interval of time

When light hits a material, it can be…

Refracted, reflected, absorbed

Define: angle of incidence

The angle made between the incident ray and the normal

Define: angle of reflection

The angle between the reflected ray and the normal

Define: ray of incidence

A ray of light that has struck a surface

Define: reflected ray

A ray of light that has reflected of a surface

Define: normal

The line that is drawn perpendicular to the surface light has reflected off

Define: point of incidence

The point at which the light strikes a surface

On what type of surface does specular reflection occur?

Flat/smooth

What type of image will specular reflection produce?

Clear

On what type of surface will diffused reflection occur?

Bumpy/rough

What type of image will diffused reflection produce?

Unclear

The angle of incidence is always ______ to the angle of reflection

Equal

Define: refraction

The bending of light rays as they travel from one medium to another, caused by a change in speed

Light travels more ______ in a denser medium

Slowly

Light travels more ______ in a rarer medium

Quickly

Light travelling from a rarer medium to a denser medium will bend ________ the normal

towards

Light travelling from a denser medium to a rarer medium will bend ________ the normal

Away from

Define: refracted ray

The ray which has entered the second medium and has bent towards or away from the normal, depending on the density of the medium.

Define: angle of refraction

The angle between the refracted ray and the normal

Define: emergent ray

The ray which emerges after reflection, refraction and dispersion

When a wave travels into a denser medium, the frequency _________

Stays the same

When a wave travels into a denser medium, the wavelength ________

Decreases

When a wave travels into a denser medium, the wave speed ________

Decreases

Define: dispersion

The phenomenon of splitting white light into its component colours (violet, indigo, blue, green, yellow, orange, red) by shining it through a prism

Are electromagnetic waves transverse or longitudinal?

Transverse

Electromagnetic waves oscillate ________ to the direction of energy transfer

Perpendicular

In a vacuum, electromagnetic waves travel at:

3X10^8 km/hr

Do radio waves have a short or long wavelength?

long

Do radio waves have a high or low frequency?

low

Do gamma rays have a short or long wavelength?

short

Do gamma rays have a high or low frequency?

high

What is the order of the regions of the electromagnetic spectrum, decreasing in wavelength?

Radio waves, microwaves, infrared radiation, visible light, ultraviolet light, x rays, gamma rays

What types of electromagnetic waves can be used in communication?

Radio waves, microwaves, infrared radiation, visible light

What types of electromagnetic waves are ionising?

Ultraviolet light, X rays, Gamma rays

Electromagnetic waves can be:

Reflected, absorbed, transmitted

True or false: Radio waves have the lowest frequency and longest wavelength

True

Can Radio waves be produced using a direct current or an alternating current?

Alternating

Oscilloscopes are used to…?

Display the wave frequency of an alternating current

The three types of radio waves are:

Long waves, short waves, very short waves

True or false: short waves can bend/diffract around the surface of the earth

False, only long waves can do this

What is Total internal reflection?

Complete reflection of a light ray reaching a boundary greater than the critical angle.

What is the critical angle?

The minimum angle at which total internal reflection takes place.

When is the angle of incidence called the critical angle?

When the angle of refraction is 90 degrees

What are some uses of total internal reflection?

Fibre optic broadband cables
Medical endoscopes

What is diffraction?

The bending and spreading out of waves as they go through a gap or past the edge of a barrier

True or false: the narrower the gap, the more diffraction will occur

True!

True or false: the shorter the wavelength, the more diffraction will occur

False: the longer the wavelength, the more diffraction will occur

What are some uses of infrared rays?

Remote controls, infrared photography, infrared communication

REQUIRED PRACTICAL 7 - What is the set-up for the required practical on measuring the speed of water ripples using a lamp?

The signal generator attached to the dipper of the ripple tank can create water waves at a set what?

Frequency

What does the lamp allow you to do?

It allows you to see the wave crests on a screen below the tank

How do you work out the wavelength of the waves?

You can measure the distance between shadow lines that are 10 wavelengths apart and then divide this distance by 10 to get the average wavelength.

Sine you have worked out the wavelength, and already know what the frequency is, which equation can be used to work out the speed of the waves?

Velocity = frequency x wavelength

ADD USES
What equipment is used to produce a radio wave (what does it do)

Transmitter → generates an alternating current which is displayed on an oscilloscope

What equipment is used to detect a radio wave (what does it do)

Receiver → creates another alternating current which is displayed on an oscilloscope

What aspect of the transmission and reception of radio waves allows information to be transferred

The oscilloscopes connected to both the transmitter and the receiver will show the same frequency

How are long radio waves used and how do they achieve this?

Sending information very long distances are the bend around the surfaces of the earth

How are short radio waves used and how do they achieve this

Sending information very long distances by reflecting between the earth and the ionosphere (part of the atmosphere) or can be used for short distances like bluetooth)

How are very short radio waves used and how do they achieve this

Sending information directly from the transmitter to the receiver. For example, television and fm radio (this is why you don’t always get good signal)

Two types of microwaves (drip…drip)

Ones that are absorbed by water molecules, and ones that are not absorbed by water molecules

How are microwaves that aren’t absorbed by water molecules used for + why? + how does this work

Satellite communication, as there is lots of water in the atmosphere. A signal is sent somewhere from earth, that is received by the satellite, and then transmitted again, and received somewhere else on earth

How are microwaves that are absorbed by water molecules used? How does it work

To heat food in microwave ovens, as most foods contain lots of water molecules → they absorb the energy from the microwaves → they vibrate faster, gaining kinetic energy → this spreads through the food by conduction or convection

Infrared radiation is emitted from all objects that BLANK

Have thermal energy

The BLANK the object the more infrared radiation it emits

hotter

How is infrared radiation used (just names, no explanation

Infrared cameras
Cooking
Electrical heaters

How is infrared radiation used in infrared cameras

Hotter objects emit more infrared radiation so they will appear closer to red on the camera, while the opposite is true for cooler objects

How is infrared radiation used in cooking

The metal is heated → it transfers infrared radiation to the food (but the waves don’t penetrate the food, so it’s only the outside that is most affected) This is how toast works.

How is infrared radiation used in electric heaters

Electrical energy is used to heat the metal of the heater, which then emits this heat to the surroundings, warming up the room

Microwaves and infrared radiation are only harmful to us in BLANK quantities

high

How can visible light be used

Communication using optical fibres to totally internally reflect the light → it can be transmitted from one place to another very quickly

(also just to see)

What must optical fibres be made of

Thin plastic or glass

Uses of ultraviolet light

Sunbeds and tanning
Fluorescent lights
Security
Water sterilisation

How is ultraviolet light used for fluorescent lights (+advantages)

They produce ultraviolet light, which is absorbed by a layer of phosphorous, which converts it into visible light, so we can see it
Very efficient → less electricity bills + co2 emissions

How is ultraviolet light used for security

Ink used which is only visible under ultraviolet light is used to mark banknotes and passports to identify frauds

How is ultraviolet light used for water sterilisation

The waves kill microorganisms

How can x rays be used to produce images

X rays are absorbed by dense materials like bones, partially absorbed by thicker muscles like the heart, and can pass through organs which are thin and mostly air like the lungs and intestines. By using a detector, we can see which rays passed through, and which didn’t, which allows an image to be produced

Why are x rays useful? How can they be harmful?

They can show injuries like broken bones, though they do give the patient a small amount of radiation (but it is a very low dose)
They are very quick and cheap
They can be harmful for the staff, who wear lead aprons to protect themselves and leave the room when x rays are being fried

How can gamma rays be used

To treat cancer cell by killing them, and produce medical images
To sterilise equipment and food

Why are gamma rays good for sterilisation (what is the alternative)

They kill microorganisms without changing the equipment/food itself, so it is safe to eat/use. The other way to sterilise would be to use boiling water, but they can damage plastic equipment

How does gamma ray sterilisation help food

It gives it a longer life because there are no microorganisms to break it down

X rays and Gamma rays can BLANK cells

damage