Waves and Optics

What is a wave?

This is a transfer of energy throughout a medium due to a disturbance within the medium.

What are the 2 types of waves?

Transverse and longitudinal waves

What is a transverse wave?

This is a wave in which the particles of the medium oscillates perpendicular to the direction of the wave. Eg. Water waves, waves on a string, electromagnetic waves-light

What are longitudinal waves ?

These are waves in which the particles of the medium oscillates parallel to the direction of the wave. Eg. Sound waves, waves on a slinky

What are the components of a transverse wave?

This consists of a series of crests and troughs.

What are the components of a longitudinal wave?

It consists of a series of compression (high pressure) and rarefractions (low pressure).

Define the term amplitude (A)

This is the maximum displacement measured from the equilibrium position (rest to crest or rest to trough). Amplitudes is measured in metres.

Define a period (T)

This is the time taken for a particle of the medium to make one complete cycle/oscillation.

Define the term frequency (f)

This is the number of wave cycles completed in one second . The SI unit is hertz (Hz). 1 hz = 1s-1

What is the formula for frequency?

T= 1/f or f= 1/T

What is a wavelength?

This is the distance between any two adjacent points that are in phase.

What is a displacement time graph?

This is a graph that shows the displacement of the particles in the medium over a period of time.

What information is obtained from a displacement time graph graph?

The amplitude

The period

The frequency

What is a displacement position graph

This is a graph that shows the displacement of the particles in the medium at an instant in time.

What information can be obtained from a displacement position graph?

The amplitude

The wavelength

What is the wave equation?

This is the equation that relates the speed of a wave to its wavelength and frequency.

What is the formula for the wavelength?

V=f×λ

What are sound waves?

These are longitudinal waves produced by objects used the vibrate. They are mechanical waves and as such require a material medium to propagate. They do not travel in a vacuum.

What is the speed of sound in dry air, fresh water, and metal?

Dry air- 350 m/s

Fresh water- 1500 m/s

Metal- 2900 m/s

What is the audible range of frequency?

This is the range of frequency detectable by the average adult human. They range from 20Hz to 20kHz.

What are sounds of frequencies below 20 Hz to 20kHz called?

Infrasonic/infrasound

What are sounds of frequencies above 20 Hz to 20kHz called?

Ultrasonic/Ultrasound

What are some animals that can detect sounds outside the audible range of frequency?

Dolphins, dogs, and bats (through echolocation)

What are some applications of sound waves?

1. Ultrasound machines which produce high frequency sounds above 20 Hz to produce images of internal organs of unborn babes

2. SONAR (Sound Navigation and Ranging) which are fixed to the base of ships or marine vessels to detect obstacles beneath the surface of the sea or the depth of the sea floor.

What determines the loudness of a sound?

This is determined by the amplitude of the sound wave. The louder the sound, the higher the amplitude.

What determines the pitch of a sound?

This is determined by the frequency of the sound. The higher the frequency, the higher the sound.

What is an electromagnetic wave?

This is a wave that has both electrical and magnetic properties. All of these type of waves are transverse waves.

What are the properties of E.M waves?

They are transverse

They travel in a vacuum

They travel at the speed of light in a vacuum (3 × 10⁸ m/s)

What are the wave phenomena?

1. Refraction

2. Reflection

3. Diffraction

4. Interference

Define reflection

This is the bouncing off of waves as it encounters a barrier

Define Refraction

This is the change in direction of a wave as it moves between two different mediums

Define diffraction

This is the spreading out of waves as it passes through a narrow opening or an obstacle

Define interference

This is the combining of 2 similar waves as they pass through the same medium

What is light?

This is a type of electromagnetic wave that forms the visible part of the electromagnetic spectrum

What are the properties of light?

1. It travels in a straight line

2. It has many individual rays

What is a shadow?

This is formed when the path of light is obstructed by an opaque object

What is a solar eclipse?

This is a type of eclipse that occurs when the light from the sun is obstructed by the moon

What is a lunar eclipse?

This is the type of eclipse that occurs when the light from the sun to the moon is blocked by the earth.

What are the light theories?

The particle theory by Issac Newton - This states that light is comprised of particles called corpuscles which is supported by light undergoing reflection and refraction.

The wave theory by Christian Huygens- This states that light is a wave. The wave double slit experiment was conducted and showed that light undergoes diffraction and interference.

The wave particle duality by Albert Einstein- This states that light can behave as both a particle and a wave.

What are the 2 types of reflection?

Normal and diffused reflection

What are the laws of reflection?

1. The incident ray, reflected ray, and the normal at the point of incidence lie on the same plane

2. The angle of incidence is equal to the angle of reflection

What is a plane mirror?

This is a mirror with a flattened surfaced

What are the features seen when an image is formed in a plane mirror?

1. The image is laterally inverted

2. The image is upright

3. The image is the same distance behind the mirror as the image is in front of the mirror. Hence, the image distance, v, is equal to the object distance, u.

4. The image is virtual

What is the refraction of light?

This is the change in direction of light rays as it moves between two mediums having different optical densities.

What are the laws of refraction?

1. The incident ray, the refracted ray, and the normal at the point of incidence all lie on the same plane

2. The ratio of the sine of the angle of incidence and sine of the angle of refraction is equal to a constant, n (refractive index).

State Snell’s law

This states that the ratio of the sine of the angle of incidence and sine of the angle of refraction is equal to a constant, n (refractive index).

What is the refractive index of a medium (n)?

This is given by the ratio of the speed of light in air (c) to the speed of light in the medium (v)

According to Snell’s law, what is the refractive index from air to medium and from medium to air?

From air to medium- n= sin of angle i/ sin of angle r

From medium to air- n= sin of angle r / sin of angle i

For a ray travelling from a less dense medium to a denser (air to glass) medium, does it refract towards or away from the normal

It refracts towards the normal

For a ray travelling from a denser medium to a less dens (glass to air) medium, does it refract towards or away from the normal

It refracts away from the normal

What is the formula used to find the refraction apparent depth?

n = real depth/apparent depth

How can light be separated into its different individual components (Colours) and how can they be recombined?

This can be done using a glass prism. This observation was first demonstrated by Sir Issac Newton. They can be recombined by placing another prism in the path of the colours, oriented upside down,

What is the critical angle?

This is the angle of incidence that produces an angle of refraction of 90^° when a ray of light travels from a denser medium to a less dense medium.

What is the formula used to find the critical angle?

sin angle C= 1/n, where n is the refractive index

What is total internal reflection?

This occurs when a ray of light travelling from a denser medium strikes the boundary at an angle of incidence greater than the critical angle of the medium.

What are the conditions for total internal reflection?

1. Light must travel from a denser medium to a less dense medium

2. The angle of incidence must be greater than the critical angle

What is the refractive index of air, glass, water, and diamond?

• Air= 1.00

• Glass= 1.62

• Water= 1.33

• Diamond= 2.42

What are the applications of total internal reflection

1. A fibre optic cable- This is used for high-speed data transmission in the form of light signals. It is made from 2 transparent glass having different refractive index

2. Endoscope- This is a medical device used for viewing internal organs without the need of surgery.

3. Mirage- This is an optical illusion that is often observed during a hot sunny day.

What is a lens?

This is a transparent material that causes light rays to refract.

What are the 2 types of lenses?

1. Convex (Converging)

2. Concave (Diverging)

What are the types of convex (Converging) lenses?

Biconvex lens and a plano convex lens

What are the types of concave (Diverging) lenses?

Biconcave and plano concave lenses

What is a converging (convex) lens?

This is a lens that is thicker in the middle than at its ends. When light rays pass through this type of lens, the meet at a point.

What are the features of a lens?

1. The optical Centre (o)- This is the centre point of a lens.

2. The principal axis (P)- This is the line drawn perpendicular to the lens that passes through the optical Centre.

3. The principal focus (F)- This is the point on the principal axis where rays of light, initially parallel to the principal axis meet after passing through the lens.

4. The focal point (f)- This is the distance measured between the optical Centre of the lens and the principal focus.

What is the lens equation?

1/f= 1/v + 1/u

What is the formula used to calculate the focal length (f)?

f= v×u/v+u

What is the formula to find the magnification?

m = v/u or hi/ho

What is the purpose of a Ray diagram?

This is used to show the position of an object by a lens.