T6: Waves

What is the difference between transverse and longitudinal waves?

What is the difference between transverse and longitudinal waves?

• Transverse: direction of oscillation is perpendicular to the direction of energy transfer

• Longitudinal: direction of oscillation is parallel to the direction of energy transfer

What is amplitude and what does it dictate?

Maximum displacement from undisturbed position of wave - loudness

What is frequency and what does it dictate?

Number of waves passing a point per second - pitch

What is wavelength?

Distance from one point on a wave to the same point on the next wave

What can happen to waves? x3

• absorbed

• transmitted

• reflected

What is the law of reflection?

i=r

Explain specular reflection

All waves are reflected in the same direction by a smooth surface. This creates a clear reflection of the image eg mirror

Explain diffuse reflection

All waves are reflected in different directions and are scattered on a rough surface. This forms a matte and not clear reflection

What is refraction?

Waves changing angles when they cross boundaries

Why does refraction happen?

New material has a different density

• More dense: wave speeds up causing it to move away from the normal

• Less dense: wave slows down causing it to move towards the normal

How do convex lens form images?

Converge the light towards the focal point

But, if the distance of the object is less than 1F then the image formed is virtual

How do concave lens form images?

Diverge light away from the focus, forming a virtual image

What are some traits that all EM waves share?

• transverse

• all same speed in a vacuum

How can we use radio waves for communication?

• Long wave lengths diffract along curvature of the earth

• Short wave lengths are reflected off of the ionosphere

How do radio waves transmit information?

1. Alternating current in transmitter produces EM waves

2. Frequency is determined by the alternating current

3. This produces a radio wave

4. This is then received by a receiver where is the energy is absorbed by the electron

5. The electron then begins to oscillate at the same frequency of the wave and so produces an alternating current that’s the same

What are some uses of microwaves?

• communication and satellites

• Microwaves ovens: vibrate water molecules causing them to increase in temperature

What is IR emitted by?

hot objects

What is a use of IR radiation?

heat detecting cameras

Describe an object at a constant temperature in terms of IR?

Emits the same amount of IR than it absorbs

How can we investigate IR?

Leslie cube

What is a use of visible light?

Fibre optic cables - not easily absorbed or scattered

What is visible light made up of?

All colours

Why do objects have a colour?

They absorb all other wave lengths eg an apple absorb all colour except red and reflects red light

A black body is…

a perfect absorber and a perfect emitter

What are some uses of UV?

suntan

What are some uses of x-rays

X-rays: easily travel through soft flesh but is absorb by denser materials like bone

What are some uses of gamma rays?

• medical tracers

• killing cancer cells

What are some risks of EM radiation?

High energy waves are ionising and so can cause mutations and cause cancer

What type of wave is sound?

longitudinal

Why can’t sound wave travel in space?

• Sound needs a medium to travel in

• But space is vacuum without any particles and so there are no particles to transfer wave energy to

Describe how we hear

1. sound waves enter the ear and hit the are drum, causing it to vibrate

2. this causes small bones called ossicles to vibrate

3. ossicles transmit the sound wave to the cochlea where vibrations are converted into electrical signal

4. these electrical signals are then sent to the brain to be interpreted

What is the human hearing range?

20≤x≤20,000 Hz

What is ultrasound?

A sound wave with a frequency greater than 20,000Hz

How can ultrasound be used in pre-natal foetus scanning?

• machines produce high frequency waves

• at the boundary between the foetus and the skin, some of the wave is partially reflected

• it is then received by the receiver and the time taken to come back is used by a computer to form an image

What are the differences between P waves and S waves?

• P waves are longitudinal and S waves are transverse

• P waves can travel through solids and S waves cannot

• P waves are faster and S waves are slower