general wave properties

  • Waves transfer energy without transferring matter.
  • Examples of wave motion include: water waves, ropes, springs

Frequency: the number of waves passing any point per second measured in hertz (Hz).​  
\[Frequency=\frac{1}{Period}\]
\[F=\frac{1}{T}\]
Period (T): time taken for one oscillation in seconds
​
Wavefront: the peak of a transverse wave or the compression of a longitudinal wave  

Speed: how fast the wave travels measured in m/s

Wavelength: distance between a point on one wave to the corresponding point on the next wave in length

​Amplitude: maximum displacement of a wave from its undisturbed point.
1) Distinguish between Transverse and Longitudinal Waves
Transverse Wave
  • Particles oscillation is perpendicular to direction of travelling wave.
  • Has crests and troughs.
  • Example: light, water waves and vibrating string
Longitudinal Wave
  • Particles oscillation is parallel to direction of travelling wave.
  • Has compressions and rarefactions.
  • Example: sound waves
2) Describe how Waves can undergo Reflection at a plane surface and Refraction due to a change of speed
Reflection: 
  • Waves bounce away from surface at same angle they strike it.
  • Angle of incidence = angle of reflection.
  • The incident ray, normal and reflected ray all lie on the same plane.
  • Speed, wavelength and frequency are unchanged by reflection.
Refraction:
  • Speed and wave length is reduced but frequency stays the same and the wave changes direction.​
When water wave travels from deep to shallow
  • speed decreases.
  • refracted towards the normal.
  • wavelength decreases.
  • frequency remains constant.
When water waves travel from shallow to deep
  • speed increases.
  • refracted away from the normal.
  • wavelength increases.
  • frequency remains constant.
3) Describe how waves can undergo diffraction through a narrow gap
  • Waves bend round the sides of an obstacle, or spread out as they pass through a gap.
  • The narrower the gap, the greater the wavelength, the more the diffraction.
  • Frequency, wavelength and speed are all unchanged.

light

4) Describe the formation of an optical image by a plane mirror and give its characteristics
Plane (flat) mirrors produce a reflection. Rays from an object reflect off the mirror into our eyes, but we see them behind the mirror. The image has these properties:
  • Image is the same size as the object.
  • Image is the same distance from the mirror as object.
  • Image is virtual: the image cannot be formed on a screen.
  • ​Image is laterally inverted.
5) ​Reflection of Light
Law of Reflection:
  • Angle of incidence i  = angle of reflection r
  • ​The incident ray, reflected ray and normal are always on the same plane (side of mirror).
6) Refraction of Light
Refraction is the bending of light, when it travels from one medium to another, due to the change in speed of the light ray.
​
Snell's Law:
  • Is a formula used to describe the relationship between the angles of incidence and refraction.
\[n_{i}sini=n_{r}sinr\]
n = refractve index
i = angle of incident
r = angle of refraction
Critical angle:
  • Angle at which refracted ray is parallel to the surface of material.
  • The light must travel from an optically denser medium to a less dense medium.
  • If the angle of incidence is greater than the critical angle there is no refracted ray, there is total internal reflection.​
Applications:
  1. Used in communications: signals are coded and sent along the optical fiber as pulses of laser light (optical fibres).
  2. Used in medicine: an endoscope, an instrument used by surgeons to look inside the body; contains a long bundle of optic fibers.
7) Describe the action of a thin converging lens on a beam of light
When parallel rays of light (travelling parallel to the principal axis) pass through a lens, they are brought to a focus at a point known as the focal point/principal focus.

Focal length: distance from principle focus and the optical center. 

Principal axis: line that goes through optical center, and the 2 foci.

​Optical center: the center of the lens
7.1) Describe the difference between a real image and a virtual image
  • Real image can be caught on a screen
  • ​Virtual image cannot be caught on a screen.
7.2) Describe the nature of image formed
Real Image
When object is further away from the optical centre than F, images can be
  • Real
  • Inverted​
  • Enlarged: if object is less than 2F
  • Diminished: if object is more than 2F 
Virtual Image
When the object is closer to the optical centre than F, images can be:
  • Virtual
  • Enlarged
  • Upright: The image is in the same vertical orientation as the object.

Example:
  • Magnifying glass: when a convex lens is used like this - an object is closer to a convex (converging) lens than the principal focus (like the diagram above), the rays never converge. Instead, they appear to come from a position behind the lens. The image is upright and magnified, it is a virtual image.

electromagnetic spectrum

8) Describe EM waves
All electromagnetic waves:
  • Travel at the speed of light in vacuum
\[3\times 10^{8}ms^{-1}\]
  • Don’t need a medium to travel through (travel through a vacuum).
  • Can transfer energy.
  • Are transverse waves.
Applications:
  • Radio waves: radio and television communications.
  • Microwaves: satellite communication and microwaves.
  • Infrared-red radiation: remote controllers for televisions and intruder alarms.
  • Visible light: in fibre optics.
  • Ultraviolet light: tanning beds.
  • X-rays: medical imaging.
  • Gamma radiation: medical treatment.

Safety issue:
Over exposure to certain types of electromagnetic radiation can be harmful. 
  • Microwaves can cause internal heating of body tissues.
  • Ultraviolet increases risk of skin cancer.
  • Infrared radiation is felt as heat and can cause skin burn.
  • X-rays and gamma rays are ionising radiation that can cause mutation leading to cancer.

sound

9) Describe Sound
  • Sound waves are longitudinal wave created by a vibrating source.
  • A medium is needed to transmit sound waves.

Example: A loudspeaker (vibrating source):
  • As the loudspeaker cone vibrates, it moves forwards and backwards, which squashes & stretches the air in front.
  • As a result, a series of compressions (squashes) and rarefactions (stretches) travel out through the air, these are sound waves.
  • The speed of sound is fastest in solid, followed by liquid, then gas (slowest).

Audible Frequency and Ultrasound:
  • Humans can hear frequencies between 20 and 20,000 Hz.
  • Ultrasound Waves (above 20,000 Hz): high frequency sound waves, medically used to look at structures and organs inside the human body, i.e. to form an image of a fetus in a pregnancy.

Echo:
  • Sound reflected off a surface, and comes back.
9.1) Describe and interpret an experiment to determine the speed of sound in air
Finding the speed of sound
  • When sound reflects off of a wall, it will come back to you; echo
  • If you know the distance between you and the wall, and measure how long it takes for the echo to sound, you can calculate out the speed of sound in air.
  • Remember to take into account that sound has gone there & back​ ​
\[velocity=\frac{2\times distance}{time}\]
\[velocity=\frac{2d}{t}\]
9.2) Loudness and pitch of sound waves
Larger Amplitude = Louder
Higher Frequency = Higher Pitch