waves

what is a transverse wave

a wave where vibrations occur perpendicular to the direction the wave is traveling

eg electromagnetic waves, water waves

What is a longitudinal wave?

a wave where vibrations happen parallel to the direction the wave is traveling eg. sound waves

define amplitude

• maximum distance between the peak or trough of a wave and it’s equilibrium point

define wavelength

the distance from one point ona. wave to the same point on the next wave

define frequency

number of waves per second

measured in hertz Hz

define the period of a wave

time taken to complete one wave cycle

the equation for wave speed

wave speed = frequency x wavelength

equation for wave frequency

frequency = 1/time period

What properties do all waves have in common?

they can be reflected and refracted

transfer energy

similarities between a transverse and a longitudinal wave

all transfer energy

can be reflected and refracted

differences between a transverse and a longitudinal wave

transverse waves vibrate at right angles to the direction of travel

longitudinal waves vibrate in the same direction as the direction of travel

what is the doppler effect?

the change in frequency and wavelength caused by relative movement of the source of wave or observer

explain why the sound of a loud object moving away from a person at a constant speed decreases in pitch

- Due to the Doppler effect

- Wavefronts emitted at constant frequency by object

- Wavefronts arrive at person further apart than when they were emitted

- Distance between wavefronts is the wavelength

- Wavelength increasing

- Wave speed = frequency × wavelength

- Speed of waves is constant

- As speed is constant and wavelength has increased, frequency must decrease

- Decrease in frequency = decrease in pitch

- e.g. when an ambulance drives past the siren decreases in pitch

Give an example of the Doppler effect in light waves

- Light from distant planets looks red (red-shifted)

- Because planets are moving away from Earth

- wavelength increases and therefore moves to the red part of visible light spectrum

What do all EM waves have in common?

All transverse waves

- All transfer energy

- All travel at the same speed (speed of light) in a vacuum

- Can be reflected, refracted and diffracted

How are x-rays and gamma rays similar?

Both short wavelength EM waves

- Carry lots of energy per second

How do x-rays and gamma rays differ?

- X-rays are made when electrons moving at high speeds are stopped

- Gamma rays are released from unstable nuclei

- Gamma is more penetrative

- Gamma has shorter wavelength

What is the difference between the wavelength of a radio wave and the wavelength of a gamma wave?

The wavelength of a radio wave is the longest, whereas a gamma wave’s the shortest

What is the difference between the frequency of a radio wave and the frequency of a gamma wave?

Radio waves have the lowest frequency, but gamma waves have the highest frequency

What is the difference between the energy of a radio wave and the energy of a gamma wave?

radio waves have the lowest energy but gamma waves have the highest energy

Describe the differences between red and violet light.

Red light have a longer wavelength, but violet light has a shorter wavelength.

Red light have a lower frequency but violet light has a higher wavelength

Red light emits lower energy, violet light emits higher energy

Which EM wave can cause internal heating of body tissue

Microwave

Which EM wave causes burns

Infrared radiation

Which EM wave can cause skin cancer and blindness

UV

How can exposure to UV rays be reduced

Wear sunglasses

Cover skin with clothes or sunscreen

Stay in the shade

What are the dangers of X-rays and gamma rays

ionising radiation

mutation leading to cancer

How can exposure to gamma rays be reduced

Wear protective lead clothing

Describe the properties of light waves.

Transverse waves

- Vibrations occur perpendicular to the direction the wave is travelling

- Transfer energy

- Can be reflected, refracted, diffracted

What is a normal line?

A line drawn perpendicular to the mirror

What is the angle of incidence

Angle between the normal and the incident ray

What is the angle of reflection?

Angle between the normal and the light ray reflecting off the mirror

What is the law of reflection?

- Angle of incidence = Angle of reflection

What is refraction?

A change in direction of waves when they travel across a boundary from one medium to another

Caused by a change in the wave’s speed.

Describe how a light ray changes direction when it enters and leaves a glass block

Bends towards the normal as it enters the block

Bends away from the normal as it leaves the block

what is the refractive index

- The extent to which light is refracted when it enters a medium

- More dense medium = greater refractive index = greater refraction of light

Give the equation linking refractive index (n), angle of incidence and angle of refraction

n= sin i / sin r

What happens when light passes from air to glass (i.e from less dense to more dense medium)?

- Light ray slows down

- Angle of refraction less than angle of incidence

- ray bends towards normal

describe an experiment to determine the refractive index of a glass block.

- Use light box to produce beam of light

- Use a ruler, pencil and paper to trace path of light

- Use protractor to measure angle of incidence and angle of refraction

- Repeat for different angles of incidence

- Repeat the same angles of incidence at least three times

- Use n = sin i / sin r to calculate average value of n

- Plot a graph of sin i against sin r

- Calculate n from gradient

define critical angle

- Angle of incidence beyond which rays of light are totally internally reflected

Define total internal reflection (TIR)

- When the angle of incidence is greater than the critical angle

- All light is reflected, none is refracted

give the equation linking the critical angle with the refractive index

sin c = 1/n

State the conditions required for total internal reflection to happen

- Medium must be from more dense to less dense

- Angle of incidence > critical angle

Explain the relationship between refractive index and critical angle

- Larger refractive index means smaller critical angle

- Total internal reflection occurs when angle of incidence is greater than the critical angle

- Total internal reflection more likely to occur when refractive index is larger

how to optical fibres work?

- Total internal reflection

- Core of fibre made out of glass with high refractive index

- Cladding is made out of glass with lower refractive index

- Light entering core is at an angle greater than the critical angle so light is reflected

give examples of the use of optical fibres

- Endoscope - used in keyhole surgery

- Communication - more information sent per second compared to old copper wiring

Describe the properties of sound waves

- Longitudinal waves

- Transfer energy

- Can be reflected, refracted and diffracted

Describe how a sound wave moves through the air

- Vibration of air molecules

- Longitudinal wave

- Regions of compression and rarefaction

- Directions of vibration and propagation are parallel