physics - topic 5: waves in matter

What direction do waves transfer energy in?

The direction they’re travelling.

What is a transverse wave?

Vibrations are perpendicular to the direction of the wave.

Examples: EM waves and ripples in water.

What is a longitudinal wave?

Vibrations are parallel to the direction of the direction of the wave.

Examples: Sound waves or springs

How can you measure frequency with a ripple tank?

• Float a cork in the tank

• When it’s at the top of a ‘bob’ start the stopwatch

• Count how many bobs pass across 20 seconds

• Divide this number by the time - this is frequency

How can you measure wavelength with a ripple tank?

• Place a piece of squared paper behind the ripple tank.

• Turn on a strobe light until the waves appear to ‘freeze’.

• Measure the distance that five waves cover. Divide this number by five to get an avg wavelength.

What happens when a wave meets a boundary? (3 things)

• Wave can be absorbed

• Wave can be transmitted at a different speed

• Wave can be reflected

Whats the rule of reflection?

Angle of incidence = Angle of reflection

What is refraction?

When waves hit a boundary at an angle and bend.

When a wave speeds up, it bends // the normal.

Away from

When a wave slows down, it bends // the normal.

Toward

Sound travels faster in denser material: true or false?

True

Light travels faster in denser material: true or false?

False - they travel more slowly.

What are the two types of reflection?

Specular (smooth surface) or scattered (rough surface).

What do you get when white light is passed through a triangular prism?

A rainbow.

Where does sound travel fastest?

Through a solid.

How do we hear sound? (5 ideas)

• Sound waves reach your eardrum through the auditory canal and cause it to vibrate

• These vibrations are passed on to the ossicles and to the cochlea.

• The cochlea turns these vibrations into electrical signals

• These get sent to the brain

• This is then interpreted as sound

How is ultrasound used? (3 ideas)

• The ultrasound waves are processed by a computer

• Used to generate an image of a developing baby

• Different distances causes different shades of black

What is sonar used for?

• Used by boats and submarines

• Can locate objects in deep water

• Can find out the distance to the seabed from water level

A higher frequency wave transfers // energy.

More/higher

What EM waves are ionising?

UV, X-rays, and gamma rays.

What are the uses of all the EM waves?

Radiowaves - Communication (radio/tv)

Microwaves - Heating food and satellite communication

Infared - Temperature monitoring cameras

Visible Light - Fibre optic comunications

UV - Tanning and

X Rays - X-Ray images (broken bones)

Gamma Rays - Sterilisation and treating cancer

What are some of the hazardous effects of ionising EM waves? (3 ideas)

• Can cause cancerous mutations

• Cell death

• Skin cancer and sunburn (UV)

What are the compromises of medical imaging with UV?

UV can only be used for soft tissue because they give a fuzzy image

How can you use medical imaging with infrared?

Hotter areas give off more IR, so IR cameras uses these differences to make an image. This is used to check people for fevers.

How is a colour of an object determined?

By what wavelengths are reflected.

What wavelengths to white and black objects reflect?

White - All

Black - None

What happens when light is shone through a convex lens?

• The rays of light are brought to a principal focus

• This is known as a converging lens

• This forms a real image

What happens when light is shone through a concave lens?

• The rays of light divert outwards

• This is known as a divergent lens

• The principal focus is behind the lens

• Concave lenses magnify an image

• This forms a virtual image

What are the steps of drawing a ray diagram?

• Draw a straight line from the top of the object to the lens, then through the focal point.

• Draw another line from the top of the object through the middle of the lens.

• The point where the lines cross is where the object is seen

• Sometimes a virtual image is formed behind the lens.