P5

Describe what a transverse wave looks like

Describe what a transverse wave looks like

A wave in which the oscillations occur perpendicularly to and the wavelength is measured peak to peak and amplitude is measured from the base to peak.

Examples of transverse waves?

Light waves
Water waves
Waves on a rope

Describe a longitudinal wave

A wave in which oscillations occur parallel to the direction of energy transfer

Properties of a longitudinal wave

Compressions- Regions of high pressure where particles have moved closer together

Rarefractions- Regions of low pressure where particles have moved further apart

Time period definition and formula

Time period- The time for which one wave takes to pass a given point

T= 1/F where F is frequency

Equation for wavespeed, frequency and wavelength

Wavespeed = Wavelength x frequency
Frequency = wavespeed/wavelength
Wavelength = wavespeed/frequency

How to measure wavelength in a ripple tank

Place a ruler on white paper underneath the ripple tank
Take a picture of the dark and light lines
Using the ruler measure the distance between the centres of 11 crests
Divide this length by 10 to find the wavelength (or 1 less than how many crests measured)

How to measure frequency using a ripple tank

Place a marker to mark a fixed point on the paper
Using a stopwatch, record the number of dark lines to pass the mark in 60 seconds
Divide the number of waves by 60 to measure the frequency

How to measure the speed of sound in the air

Make someone stand 100m away from you by measuring using a trundle wheel
Make the person bang 2 pieces of wood together
Using a stopwatch, measure the time from when you see the person bang the wooden blocks to when you hear the sound
Repeat this 5 times and take an average by calculating the mean
Calculate the speed by dividing the distance by the average time

How to measure speed of sound and wavelength using an oscilloscope?

Start with 2 microphones connected to an oscilloscope next to each other and a speaker emitting a known frequency using a signal generator.

Move one microphone away from the other until the two traces on the oscilloscope are in phase then measure the distance between microphones using a ruler

Why is sound not heard in a vacuum?

The bell vibrates
There are no particles next to it
So no sound wave is created and the energy cannot be transferred to the air outside

Different types of sound across a boundary

Reflected- echo
Transmitted- Goes through the boundary
Absorbed- similar to soundproofing

Outline the process of our ear hearing sounds

Sound waves are collected by the outer ear
The waves travel along the ear canal
The waves reach the eardrum and make it vibrate
The small bones (ossicles) amplify the vibrations
The cochlea contains fluid which transmits movement of the oval window to small hairs called cilia on the inside of the wall
Hair attached to sound-detecting cells that release chemical substances
Chemical substances make nerves send a signal down the auditory nerve to the brain

What sounds can humans hear?

Humans can only hear sound within 20Hz-20,000Hz
Sound above 20,000 Hz is ultrasound

How do ultrasound body scans work?

Ultrasound waves are produced by a transducer and transmitted into the body
The ultrasound waves are partially reflected everytime they travel into a tissue with a slightly different density
The transducer detects the reflected ultrasound waves and produces a live image on the computer screen
A gel is applied to the surface because it allows ultrasound waves to enter the body

Properties of electromagnetic waves

Always transverse waves
Can travel through a vacuum
Travel at the speed of light (300,000 m/s)

Electromagnetic spectrum in order of increasing frequency

Radiowaves (10^4)
Microwaves (10^8)
Infrared (10^12)
Visible light (10^15)
Ultraviolet (10^16)
X-ray ( 10^18)
Gamma rays (10^20)

How are Radio waves produced?

An alternating current in the transmitter produces radio waves with the same frequency. This induces a matching alternate current in the receiver

How do you communicate with radio waves

Radio waves can be used to send information from one place on Earth’s surface to another
Radio waves diffract around hills and buildings as their wavelengths are very long

Advantages and disadvantages of communicating with radio waves

Advantages:
Does not need direct line of sight between transmitter and receivers

Disadvantages:
Signal gets weaker when it diffracts
Some radio signals pass through the atmosphere but most are reflected (Conosphere)

Properties of microwaves

Travel through Earth’s atmosphere
Signal received and re-transmitted by orbitting satellites
Need a direct line of sight

How does conduction occur

Heated particles in a solid vibrate rapidly
Vibrating particles bump into their neighbours and make them vibrate
Heat is conducted along the rod as vibrating particles transfer the energy

How does a normal convection oven work

Heats all the particles on the surface of the food
These particles gain kinetic energy
Heat is transferred through to centre of food by convection or conduction

How do microwaves work

Causes only water or fat molecules to gain kinetic energy
Can penetrate up to 1 cm below surface of food
Heat is transferred through the food via convection

Properties of infrared radiation

Heat can be transferred without particles as an EM wave
Everything above absolute 0 emits IR radiation
Dark, matte surfaces are good emitters and absorbers

White or shiny surfaces are good reflectors of IR radiation

What are the primary colours of light and what do they combine to make?

Red, Green, Blue
Red + green = yellow
Red + blue = magenta
Blue + green = cyan

Difference between specular reflection and diffused scattering

Specular reflection- from a smooth surface in a single direction. An image is seen in the reflection
Diffuse scattering- reflection from a rough surface that causes scattering in many directions

Properties of opaque, translucent and transparent objects

Opaque- transmit no light, absorbs some wavelengths, reflects some
Translucent- transmits most wavelengths of light, Absorbs and reflects some light
Transparent- Transmits all wavelengths of light, Absorbs and reflects some light

Dangers of high energy radiation

UV, X-rays and Gamma rays contain ionising radiation which can damage you
Ionising radiation can damage the DNA in cells
Damaged DNA could mutate, leading to uncontrollable division (cancer tumours)
Damage is more likely to occur to actively dividing cells in the body

Benefits and dangers of UV light

Benefits: When UV passes through the skin, it stimulates vitamin D production. Vitamin D is essential to the absorption of calcium.

Dangers: sunburn, skin cancer, cataracts, premature skin aging

How are X-ray images formed

X-rays transmitted through the body while detector placed behind the patient
X-rays pass through patient’s body and onto the detector. Film turns black where x-rays hit it
Dense substances like bone absorb x-rays so the film stays white where bones are

How are CT scans and medical tracers different to x-rays

CT scans- take a range of x-rays from various positions and processed by a computer to build a 3D image from cross sections
Medical tracers- A type of imagery that uses X-rays and Gammara rays

How does a gamma knife work

Fire a narrow beam of low intensity gamma rays at the affected area
This beam focused onto the cancerous cells
By rotating the beam around the patient, cancer cells will receive high dose of gamma rays whilst healthy cells receive a low dose

How are gamma rays used for sterilisation

Food can be hit with high doses of gamma rays to kill bacteria
Keeps them fresh but does not make them contaminated
Medical equipment can be sterilised in the same way

Properties of refractions

When light enters a more dense medium, light slows down and bends towards normal (shorter the wavelength, more it bends towards normal and blue slows down most)

When light enters a less dense medium, it speeds up and bends away from the normal

Which colours have largest/smallest refractive index

Different colours travel at different speeds through glass, so each has a different refractive index
Violet traces slowest so have largest refractive index
Red traces fastest so has the smallest refractive index

Describe refraction practical

Place Persplex block on white paper and trace outline then draw a normal at right angle to the long side of block, passing through the middle of the block
Use a protractor to draw incident rays at 20,40,60 degrees from the normal
Shine a single beam of light along first incident ray line, where it exits the block on the other side and to the edge of paper
Remove block and ray box and join up dots using pencil and ruler

Rules for convex ray diagrams

Any ray that hits lens perpendicular to the axis will pass through the “further” focus
Any ray hitting centre of lens will pass through without changing direction

Image formed in a concave lens

Upright, Virtual, Diminished and Inside 1st focal point

How to describe images from lenses

Real/Virtual- Real: Rays meet on other side of lens, Virtual: rays don’t meet and only meet on same side of lens
Upright/inverted
Magnified/Diminished

Which lenses used to fix which eye problems

Myopia- fixed by concave lens with focal point in front of retina. Lens diverges light back into focus

Hyperopia- Convex lens with focal point behind retina. Converges light to bring it back into focus