Waves

What are the 2 types of waves?

• Transverse waves

• Longitudinal waves

What is a transverse wave?

A wave for which the oscillations are perpendicular to the direction of energy transfer

What is a longitudinal wave?

A wave for which the oscillations are parallel to the direction of energy transfer

What are 2 examples of tranverse waves?

• Electromagnetic waves

• Seismic S waves

What are 2 examples of longitudinal waves?

• Sound waves

• Seismic waves

What are the 2 parts of a longitudinal wave?

Compressions and rarefractions

What is amplitude?

The maximum displacement of a point on a wave from its undisturbed position

What is wavelength

The distance from a point on a wave to the same position on the adjacent wave

What is frequency?

The number of complete waves that pass a point in a second, in hertz (Hz)

What is wavespeed?

The speed at which the wave moves or at which energy is transferred through a medium.

What is the point of a wave?

To transfer energy from 1 point to another through a medium

What equation links wavespeed, frequency and wavelength?

Wavespeed = frequency x wavelength

What formula links frequency and time period?

1 (wave cycle) = frequency x time period

What is it called when a wave bounces off a surface?

Reflection

How do sound waves travel in a solid?

They are absorbed by the solid, in which the solid particles vibrate to the frequency of the sound wave the solid absorbed

What is the range of human hearing?

20Hz - 20kHz

Why is human hearing limited?

Within the ear, sound waves cause the eardrum and other parts of the ear to vibrate, however, the conversion of sound waves into vibrations of solids only works over a limited frequency range.

What are ultrasound waves?

Waves with a frequency greater than the upper limit of human hearing (20kHz)

What are uses of ultrasound waves?

Medical or industrial imaging

How are seismic waves produced naturally?

Earthquakes which produce both S and P waves

State a difference between the mediums that P-waves and S-waves can travel through

• P-waves travel through both solids and liquids

• S-waves only travel through solids (not liquids)

What technique is used to detect objects in deep water and measure water depth?

Echo sounding:

• High frequency sound waves are emitted, reflected and detected

• Time difference between emission and detection, alongside wave speed, are used to calculate distances

What 3 things can happen at a boundary?

Transmission, reflection and absorbtion

What type of spectrum is the electromagnetic spectrum?

A continuous spectrum

Order the types of electromagnetic radiation from lowest to highest frequency.

• Radio waves

• Microwaves

• Infrared

• Visible Light

• Ultraviolet

• X-rays

• Gamma Rays

Why can EM waves travel in a vacuum and air?

EM waves are vibrating electric and magnetic fields, so they dont require physical particles to transfer energy

What property of waves in different mediums causes refraction?

• Velocity

• Wave speed is slower in denser materials, causing refraction

Where do waves refract in a denser medium?

Towards the normal

Where do waves refract in a less dense medium?

Away from the normal

What waves can be produced by a circuit?

Radio waves

How do radio waves create alternating current in a circuit?

They induce oscillations in a circuit with the same frequency as the waves themselves

Where do gamma rays originate from?

The nuclei of atoms (released by radiation)

What health effects do UV waves cause?

• Premature skin ageing

• Increase risk of skin cancer

What health effects can X and gamma rays cause?

• They are ionising radiation, so increase the chance of gene mutation

  • Increase risk of developing some cancers

What are 3 practical uses for infrare radiation?

• Heaters

• Thermal cameras / imaging

• Cooking food

What are 2 uses for microwave waves?

• Satellite/mobile communication

• Cooking food

What are 2 uses of radio waves?

• Television transmission

• Radio transmission

What allows lenses to form an image?

Refraction

How does a convex lens form an image?

Parallel rays of light are refracted and brought together at a point known as the principal focus

What is the focal length of a lens?

The distance from the lens to the principal focus

What is the magnification formula?

Magnification = image height / object height

What is the difference between the image produced by a convex and a concave lens?

• Convex lenses can produce real or virtual images

• Concave lenses can only produce virtual images that are upright and diminished

What determines colour of a wave?

The wavelength and frequency of waves

What is specular reflection?

Reflection on a smooth surface, where light rays are reflected in a single direction

What is diffuse relfection?

Reflection on a non smooth surface, which causes scattering

How does a colour filter work?

• A colour filter absorbs all wavelengths of light other than those in its range of the spectrum

• This means only the filters colour light passes through the filter

When does an object appear white?

When it reflectes all wavelengths at equal amounts

When does an object appear black?

When it absorbs all wavelengths of light

What is a body?

An object

What is a perfect black body?

An object that absorbs all EM radiation, and is also a perfect emitter of infrared radiation

Why is a perfect black body the best possible emitter of radiation?

It is a perfect absorber since it absorbs all radiation incident on it, and since perfect absorbers are perfect emitters, it is a perfect emitter too

What can be said about a body when it increases in temperature?

A body at constant temperature is absorbing radiation at the same rate as it is emitting radiation. The temperature of a body increases when the body absorbs radiation faster than it emits radiation

Give two factors that affect the temperature of the Earth.

• The Earth’s rate of absorption and emission of radiation

• The amount of reflection of radiation into space