Unit 1: Chapter 5 - Waves

Question 1

The Nature of Waves

Answer 1

Electromagnetic Waves can all travel through a vacuum at the same speed 300,000 kilometre/s.

Electromagnetic waves are all TRANSVERSE. Transverse waves oscillate perpendicular.

MECHANICAL/LONGITUDINAL WAVES consist of SOUND, WATER, waves of springs and ropes, as well as seismic waves.
Mechanical waves push and pull and travel through the air. These waves compress also do rarefaction.

Question 2

Measuring Waves

Answer 2

The AMPLITUDE consists of peaks and troughs. The distance from peak to peak is on complete wave. This is also known as the WAVELENGTH.

The FREQUENCY is the number of waves/s. The unit is Hertz (Hz).

The wave speed is the distance travelled by a wave crest every second. (Metres/second)

Wave Speed (m/s) = frequency (Hz) X wavelength (metre)

Question 3

Wave Properties: Reflection

Answer 3

Angle of incidence = Angle of reflection

When drawing ray diagrams of a plane mirror, remember to draw the actual ‘image’ and the ‘point object’.

REAL AND VIRTUAL IMAGES

The image of a mirror are back-to-front but not upside-down.

A virtual image can’t be projected on to a screen like movie images that you see at a cinema.

An image on a screen is described as a real image because it forms by focusing light rays on to the screen.

Question 4

Wave Properties: Refraction

Answer 4

Refraction is the changing of direction when moving through different densities. For example, glass to air or air to glass.

FROM GLASS TO AIR:

• Towards from normal.
• Angle R is greater than Angle I

FROM AIR TO GLASS:

• Away from normal
• Angle R is smaller than Angle I

REFRACTION BY A PRISM

Splits the colours of the spectrum of a a white light. Each colour is refracted slightly differently.

Question 5

Wave Properties: Diffraction

Answer 5

Diffraction is the spreading of waves when they pass through a gap or past the edges of the obstacle can spread out.

AT WIDE GAP:
Wave diffract slightly

AT NARROW GAP:
Waves diffract more

To diffract, the wavelength must be the same length as the gap.

DIFFRACTION OF LIGHT
- Hubble Space Telescope - Focusing mirror is 2.4m in diameter. Little diffraction occurs because it is so wide and so images are very clear and focused.

DIFFRACTION OF ULTRASONIC WAVES

Frequencies are higher than the human ear and can be used to see images of foetuses in the womb. If the transmitter is too narrow, the waves spread out too much and the image becomes unclear.

SIGNAL PROBLEMS

People in hilly areas have poor reception as the waves to do not reach the receiver. By passing on top of the hill, the waves are diffracted but not enough behind the hill.

Question 6

Sound

Answer 6

Sound waves cannot travel through a vacuum. This is because sound depends on vibrations of air. In a vacuum, there isn’t any.

REFLECTION OF SOUND

An echo is a reflection of sound. If the material of the reflected sound is absorbing, such as soft fabric, the sound will be absorbed instead of reflecting and no echoes will be heard.

Refraction takes place between different layers of air at different temperatures.

In the daytime, sound refracts upwards, not downwards. because the air is warmer than the air higher up.

The human ear ranges from 20Hz to 20,000 Hz.

Question 7

Musical Sounds

Answer 7

Increasing LOUDNESS of a SOUND increases height of the AMPLITUDE of the waves.

Increasing PITCH increase the frequency of a sound.

MUSICAL INSTRUMENTS

When the air vibrates inside the instrument, the cycles of vibration grow stronger at certain frequency. We say the instrument RESONATES.