physics - waves, topic 6, paper 2

year 10 feb-june

what is a wave (3)

-transfers energy from 1 place to another

-most waves transfer energy through vibrations (oscillations) of particles in space

-these particles don’t move from 1 place to another but they vibrate around a fixed point

define wave

a vibration (oscillation) that transfers energy from place to place but not matter

transverse waves definition

when the vibration is at a right angle to the direction the energy is moving (perpendicular) e.g electromagnetic waves

longitudinal waves definition

waves when the vibration is parallel to the direction of the wave is moving e.g sound waves

difference between a transverse wave and a longitudinal wave (3)

-longitudinal waves vibration is parallel to the direction of the wave moving

-whereas transverse waves are when the vibration is at a right angle to the direction the energy is moving

-oscillations!!!

longitudinal waves vibration is parallel to the direction of the wave moving whereas transverse waves are ehre when the vibration is at a right angle to the direction the energy is moving

label both waves

what’s the wavelngth symbol and definition

upside down y

the length between 2 peak/ areas of compression

amplitude symbol unit and definition

A

m

half the hight of the wave

frequency (symbol, unit, def)

f

Hz

the number of waves that pass a point every second

period (symbol, unit def)

T

s

the time it takes for a complete wave to pass a point

why can’t astronaughts hear sounds outside their space suits (2)

-sound can’t travel through empty space

-as there are no particles to vibrate

diff waves travel at diff speeds

what does the speed of a wave depend on

the medium (substance) the wave is travelling through

wave speed, frequency, wavelength equation

wave speed (V)(m/s)= frequency(f)(Hz(are every second) X wavelength(λ)(m)

1, frequency, period equation

frequency (f)(Hz)= 1/period(T)(s)

why do the waves appear stationary during the ripple tank RP

-frequency of waves is equal to frequency of the strobe light

whats the electromagnetic spectrum

spectrum of waves that are of the same type of wave but have slightly diff wave properties (wave length + frequency)

what waves are on the electromagnetic spectrum(7)

radio (highest wavelength, lowest frequency)

microwaves

infrared

visible

ultraviolet

xray

gammarays (shortest wavelength, highest frequency)

radio waves

whats it used for (3)

+description

• on earth communication

• allow us to listen to music transmitted by radio stations at diff frequencies

-when you tune into diff radio stations, you tune into diff radio frequency and canges the transmission you are listening to

• radio communication

microwaves

what they do

+description

-heat food

-food absorbs microwaves-causes our food molecules to vibrate and heat up

-satellite communication- uses microwaves to communicate with other satellites and earth- can easily get through atmosphere

Infrared

what they do

+description

-infrared radiation emitted by warm objects

-used in electrical heaters

-infared cameras- see things when there is little to no visible light

visible light

what they do

+description

-the frequencies of the electromagnetic spectrum that humans can see

-used in high speed communication

-fibre optic cable uses visible light to transmit into at incredibly high speeds

Ultra violet

what they do

+description

-sun emits lots of ultra violet (UV) radiation

-UV radiation is higher frequency than visible light so exposure to too much UV can damage your skin and even cause skin cancer

-UV radiation can also be used in energy efficient lighting and light bulbs

-we also use UV to sterilise medical equiptment and food

X ray

what they do

+description

-medical imaging

-image bones-relatively safe in small doses but it can be damaging to the body if you are exposed to too much- because x-ray radiation is high frequency therefore can cause mutations in your cells which could lead to cancer

gamma rays

what they do

+description

-highest frequency electromagnetic wave

-highly ionising- can damage cells-use gamma rays in cancer treatment

-gamma rays directed at cancer cells in the body in order to kill those cells

-can be used in stronomy-highly penetrating and so we can use it to see things very distant in the universe

speed of light

300,000,000 m/s

OR
3 × 10⁸ m/s

electromagnetic waves in a vacuum equation

C = λ x f

1. how are radio waves transmitted

2. how are waves picked up- what do electrons do in the reciever and what does it lead to

3. how can this be represented

4. why can radio waves be used for long disrance communication

1. transmitted- transmitter at a certain frequency

2. picked up- reciever- where electrons in the receiver vibrate/ oscillate at the same frequency as the radio waves were transmitted at. This leads to an alternating current in the reciever

3. an oscilloscope can be used to represent this recieved radio transmission

4. radio waves can be used for long distance communication because their long wavelength allow them to bend around the curvature of the Earth

why are microwaves used for heating food

high frequency microwave radiation is absorbed easily by food molecules, increasing their internal energy and raising their temp

why are infared used forheaters and heating food

certain frequencies can be abdorbed easily by chemiscal bonds, increase their internal energy and raising their temp

why are gamma and xrays used for medical imaging

penetrating so will pass through most body tissues

why are gamma rays used for space exploration

highly penetrating so can pass through clouds of gas/ other objects in universe so we can take pictures from far away

P waves

what does it stand for

what are they

what can they pass through

primary waves

longitudinal waves- fastest of waves produced by earthwuakes

can travel through liquid and solid

S waves

what does it stand for

what are they

what can they pass through

Secondary waves

transverse waves- slower waves

onkly travel through solids

what parts of the earth can P and S waves travel through

Crust- solid so P and S waves

mantle- solid so P and S waves

outer core- liquid so only P waves

inner core- solid so P and S waves

2 waves sound waves and radio waves are diff

1. radio waves are transverse, soundwaves are longitudinal

2. radio waves travel at a higher speed than sound waves

reflect definition

where waves ‘bounce back‘/ bounce off a surface

absorb definition

where a surface ‘takes in‘ some of the energy from a wave that hits it

refract definition

where waves change speed and bend at a barrier between two mediums

transmit definition

when an object allows a wave to pass through it

emit definition

where an object gives out a wave

if a object/person absorbs more radiation than they emit will they heat up or cool down

if a object/person emits more radiation than they absorb will they heat up or cool down

heat up

cool down

what are white'/ shiny objects good for

reflecting

bad at absorbing or emitting radiation

what are black/ matte objects good for

absorbing/ emitting

poor at reflecting

out of

matte black

matte copper

shiny copper

matte red

which ones the best emitter of radiation

why

matte black

matte red

matte copper

shiny copper

because matte black has the highest temp as it emitted the most infarred radiation

how does the earth stay warm (4)

• most wavelengths of electromagnetic radiation emitted by the sun are transmitted through the earths atmosphere

• earth absorbs short wavelengths and warms up. Other wavelengths reflect off the earth

• greenhouse gases in the atmosphere absorbs some of the infrared radiation reflected off the earth- warming the lower atmosphere

• the longer wavelength infrared is transmitted through the atmosphere and back into space

whats the perfect black body

a (black) object that absorbs all the radiation that hits it so nothing is reflected

would a hotter object

emit a higher/lower wavelength

higher/lower frequency radiation

lower wavelength

higher frequency radiation

would a cooler object

emit a higher/lower wavelength

higher/lower frequency radiation

higher wavekength

lower frequency radiation

is the peak of a hotter object be a shorter or longer wavelength than a cooler object

shorter wavelength

does a hotter object emit a wider or narrower range of wavelngths than a cooler object

wider range of wavelengths

2 diff between electromagnetic waves and sound waves

• electromagnetic waves are transverse, whereas sound waves are longitudinal

• electromagnetic waves travel at a higher speed compared to sound waves

measuring waves

list the equiptment needed to calculate the speed of water waves (5)

ripple tank

stobescope

ruler

motor

wooden block

describe how to measure the speed of waves in a string (4marks)

-turn up frequency on the single generator

-write down frequency

-use a ruler to measure length of the wave

-use the wave equation to calculate the speed of wave

Snell’s law

reflection diagrams can be quite simple to complete, because of Snells law

the angle of incidence = angle of reflection

Seeing colour

why does a red ball appear red to our eyes

when we look through a green filter most things appear green, why

why does a snowman appear white

what do black objects absorb

1. because it absorbs all other wavelengths except red

2. this is because the filter only transmits green wavelengths and absorbs all others

3. because it reflects evry wavelength of visible light, white objects do not absorb any wavelength of light

4. black objects, absorb every wavelength of visible light, and reflect no wavelength of visible light

what are the two types of reflection

specular reflection= occurs on mirrors, where surfaces are (almost) entirely smooth. Here the reflection is very orded

diffuse reflection = happens on other objects, that have rougher surfaces. Due to theroughness of the surface the reflections are irregular

ray diagrams and howto describe the motion

what do ray diagrams have (5)

-labelled rays

-directional arrows

-labelled angles

-a normal

-straight linaes

what colour does the ball apear

white light →red filter, white ball

white light→green filter, red ball

ball appears red because the filter only transmits red wavelengths and absorbs all others and reflects of the ball

ball appears black as green is transmitted through the filter, greenlight is absorbed by red ball

investigating retraction diagram

what do you notice when the light ray enters the glass block

the light ray slows down as it enters the glass block. What can we conclude about the density of the block compared to the air

the light ray refracts

the block is denser than air

wave fronts

A wave front diagram is a way of representing multiple waves. Each line on the wave front diagram represents the same point on each of these waves

for example a wavefrontdiagram might represent thr trough or peak of each wave with one straight line

when we use these wave front diagrams to represent refraction we see that the wave front bends when it hits a boundary at an angle LOOK IN BOOK 30 APRIL

what happens to the wavelength during reflection

what happens to the frequency

wavelength gets smaller and the waves slow down so the frequency stays the same

speed = smaller too

what is sound

-sound waves transfer energy from one place to another

-sound is a longitudinal wave with areas of rarefraction and compression

-sound involves the oscillation of particles, parallel to the direction that the energy is moving

-sound can only travel where there are particles to vibrate

the ear: how we hear

• in the same way that our eyes are able to convert electromagnetic waves into brain signals (allowing us to see), the ear converts sound waves into brain signals that allow us to hear

• sound waves hit the ear drum, causes small bones in the inner ear to vibrate. The cochlea then converts these vibrations to nerve signals - allowing our brain to work out what we have heard

what are oscilloscopes used for

converting sound waves into viewable transverse waves

moving sounds

objects that are emitting waves - arent always stationary

The doppler effect

• when a wave emitting object moves towards you the wave frequency inc causing the sound to seem higher pitched

• when wave emitting objects move away from you the wave frequency decreases causing the sound to seem lower pitched

Ultrasound - image babies in the womb

-humans can hear 20-20,000 Hz (but other factors can impact the range an individual can hear e.g listening to loud music, age)

-ultrasound = a sound that is a higher frequency than what humans can hear

-a transducter = a piece of electronic equipment that emits ultrasound into the womb, this ultrasound hits the baby + reflects back

-reciever = what the reflected ultrasound is picked up by. The length of time between the ultrasound is emitted and when its recieved allows us to image the baby

convex / converging lenses

-parallel rays of light are refracted inwards and meet at the focus

-focus is infront of the lens

concave/diverging lens

-spreads light rays out

-focus behind the lens

-used for short sighted

Practicle: measuing focal length

method

1. we measured the focal length for the convex lense by using a ray block and the slit card on the 3 hole side. We put the convex lense when the light is still parallel and draw an X (this is the focus) in the middle of where the light rays meet. Trace around the convex lense. Take of the lense and measure from the middle of thw width of the lense to the focus. THis is the focal length

2. we measured the focal length for the concave lense by using the ray block. Put the concave lense where the light is still parallel and trace the lense. Trace the 3 rays and remove the lense. Measure where the rays meet behind the lense (side closer to ray box) abd put an X (focus) then measure from the focus tpoint to the middle of the width of lense. This is the focal length

Practicle: measuing focal length

equipment

-ruler

-paper

-power bank

-ray box

-lenses

-rubber

-slit

-pencil

magnification equation

if magnification is >1

if magnification <1

magnification = image height/object height

if magnification >1 then object will be magnified (bigger)

if magnification <1 object will be dimminished (smaller)

Real vs Virtual images

LOOK IN BOOK FOR DIAGRAM 11 JUNE

-real images are locations where light actually converges (rays being brought together)

-real images would be visible if a screen is placed there

-virtual images are located where light appears to come from

-virtual images can only be seen when looking through the lense

upright vs inverted images

LOOK IN BOOK FOR DIAGRAM 11 JUNE

-upright images would appear the same way up as the object

-inverted images would appear upside down

-if the object is moved further away from the lense the size of the image will decrease

convex lense thats futher than 2 focal points

convex lense thats between F and 2F

convex less than F

concave at any location

are they diminished or magnified, upright or inverted, virtual or real

DIR

MIR

MUV
DUV

wave speed on a string

experiment

A string is attached to a vibrator and passes over a pulley. The weights on the end of the string keep the strings in tension.

The signal generator is used to change the frequency of the vibrator

when the signal generator is switched on, the vibrator “shakes” the string and sets up a wave pattern. (This is just the same as a vibrating string on a guitar)

becuase the ends of the string are fixed, it can only vibrate so that there are a whole number of half wavelengths on the string

FInd the frequencies at which these patterns occur and use the ruler to measure the wavelength (count the number of half wavelengths on the string)

Wave speed on a string

theory

The wave patterns on the string are called “stationary waves” or “standing waves”

they form because a wave travels along the string and reflects at the end. The two waves, moving in opposite directions, add together to form the stationary wave pattern

to find the speed of the wave, use the formular: = frequency x wavelength