P4 Waves

Waves

 

• Wave motion transfers energy without transferring matter in the direction of wave travel.

• A wave is an oscillation, such as ropes and springs and water waves.

• Transverse waves are waves whose direction of oscillations is at right angles to the direction of propagation(direction.) e.g. Electromagnetic waves. It has troughs and crests.

• Longitudinal waves are waves whose direction of oscillations is parallel to the direction of propagation. E.g. Sound waves. It has compressions and rarefactions.

• Speed is how fast a wave is traveling.

• Wavelength is the distance between successive crests of a wave.

• Amplitude is the maximum extent of a vibration or oscillation, measured from the position of equilibrium; absolute value of displacement.

• Frequency is the number of complete waves passing a given point in one second, measured in Hertz (Hz).

• Wavefront is a line joining neighbouring points which are in phase.

 

• • Normal: the line perpendicular to the surface at the point of incidence.

 

• Speed (m/s) = frequency (Hz) * wavelength (m)

 

Wave reflection and refraction

• • Reflection of wave in a smooth plane barrier: Angle of incidence = Angle of reflection
  • A change in wavelength may cause light to change direction and speed

 

• Refraction is a deflection of wave passing obliquely through the interface between one medium and another or through a medium of varying density.

 

• Water waves travel faster in deep water than in shallow.
• Experiment to determine refraction: use glass block to show.

Sound waves

• • Sound waves are produced by vibrating sources which causes the medium around it to vibrate.
  • Sound waves are transmitted by compressions and rarefactions.
  • Sound waves must need a medium to travel, it is a mechanical wave.

 

• Human range of audible frequencies: 20 to 20,000 Hz

 

• • Using data logger and long distances to measure speed of sound in air
  • Sound travels fastest in solids, then liquids, then air because molecules are packed tighter.

 

• Louder sound has higher amplitude.

• Higher pitch has higher frequency.

 

• Echo is a reflection of sound that arrives at the listener with a delay after the direct sound, the delay is proportional.

Electromagnetic spectrum

• All are transverse waves
• All travel through vacuum
• All travel at light speed of 300,000,000 m/s

 

Wave	Function
Radio waves	Radio and television communications
Microwaves	Satellite tv and telephone communication, cookimg
Infrared	Remote controllers for tv and intruder alarms
X-rays	Medicine and security

X-rays can cause cancer as they can make cells mutate. Hence, dosage of waves must be kept small.

Microwaves make water vibrate and hence cells may be damaged by the heat energy given by the microwaves.

 

Light waves

• • Optical fibres can carry information coded in light or infrared signals, and they are used in medicine to transmit image and in communications to transmit data.
  • Optical fibres has light undergo total internal reflection.
  • Critical angle: the angle of incidence for which the angle of refraction is 90°.

 

• Total internal reflection: the wave cannot pass through by refraction and is entirely reflected, and this is when angle of incidence is beyond the critical angle.

• Principal focus: The point labeled F on the diagram, where the light rays come together to form a real image.

 

• Focal length: the distance between the centre of a lens or curved mirror and its focus.
• When the object is located at the focal point, no image is formed.
• When object is beyond 2F, image will be inverted, small and real
• When the object is located at 2F, image will be inverted at 2F.
• When object is between 2F and F, image will be enlarged, inverted and real.
• When object is located in front of the focal point, image will be virtual, enlarged and upright.
• All light rays should pass the focal point somehow on ray diagrams.

 

Dispersion

Dispersion is when white light passes through a prism and splitted into a spectrum.

Dispersion happens because the different spectral colours travel at the same speed in a vacuum, but at different speeds in a medium such as glass. Amount of bending increases as change in velocity increases.

P4 Equations:

• • Wave Speed (m/s) = frequency (Hz) * wavelength (m)

 

• Reflection: Angle of incidence = Angle of reflection