Waves and Optics 2

What is the amplitude?

the maximum displacement of the oscillation from its undisturbed position.

What are two ways to talk about the undisturbed position?

mean position or equilibrium position.

If the amplitude of a light wave increases what happens?

the light becomes brighter

If the amplitude of a sound wave increases what happens?

the sound becomes louder

What is a progressive wave?

Waves that transfer energy from point one to the next

What does it mean when points are in phase in a progressive wave?

They have the same displacement, direction and speed in their vibrations.

How are sound waves produced?

through vibrating systems

How do sound waves travel?

through a material medium

What is fluorescence?

high frequency radiation such as UV is absorbed by certain substances and is then emitted as visible light of lower frequency

What is a wavefront?

A line perpendicular to the propagation of a wave on which all points are in phase.

How do scientists know that sound waves reflect?

The echo produced when a loud sound is made Infront of a cliff

Other than echoes, how do scientists know that sound waves refract?

At night time, the air in contact with the ground at night is cooler. When sound travells upwards, the speed increases as it enters layers of warmer air. This causes the wavefronts to seperate, refracting along a curved path.

When sounds travel at night, what does the combination of warm and cool air result in?

It results in more sound energy getting to the observer.

What is diffraction?

The spreading of a wave as it passes an edge or goes through a gap.

What is interference?

when two or more waves superpose on each other to produce a combined vibration of amplitude lesser or greater than any of the individual waves

Explain how Young's Double Slit experiment is conducted

A monochromatic source of light is set up to diffract through two narrow slits, about 0.5 mm apart. After this, the emerging wavefronts move towards a translucent screen where they superpose and form an interference pattern of bright and dark fringes. The experiment is performed in a poorly lit room.

What is a ray of light?

The direction in which light propagates

What is a beam of light?

A stream of light energy

When is a shadow produced?

When an opaque object obstructs the path of light

What is an umbra?

A total shadow of uniform obscurity

What is a penumbra?

A partial shadow gradually becoming fainter towards its outer edge

Can sound propagate through a vacuum?

no

What does a greater frequency wave produce?

sound of a higher pitch

What is a frequency below 20 Hz called?

infrasound

What is the audible range of the average human?

20 Hz to 20 kHz

What is a frequency above 20 kHz called?

ultrasound

If the amplitude is high, what does that mean?

The loudness of the wave will be high.

A high frequency wave will have what?

A high pitch

If the amplitude is low, what does that mean?

This means that the loudness of the wave will be low.

A low frequency wave will have what?

A low pitch

Describe how sound is produced and propagated in a medium

Sound is transmitted as a longitudinal wave and is produced by vibrating systems.

What are some uses of ultrasound?

Communication between dolphins, measuring distance and diagnostic imaging.

Explain how dolphins use ultrasound to communicate

they emit and receive ultrasonic vibrations

Explain how ultrasound is used to measure distance

Bats determine distances by emitting ultrasound and assessing the time in which the echoes return

Explain how ultrasound is used for diagnostic imaging.

Ultrasound is partly reflected when it strikes the boundary between different materials. Doctors use a probe to direct ultrasonic waves into the patient. The reflected waves, received by the same probe, are analysed by a computer to produce an image on a screen.

What is an electromagnetic wave?

a group of transverse waves consisting of an eletric field and magnetic field which vibrate perpendicular to each other and to their direction of propagation

What are some general properties of electromagnetic waves?

they are all transverse waves
they travel at the same speed of 3.0 x 10^8 (through a vacuum or air)
they can propogate through a vacuum
they consists of varying electric fields and magnetic fields

Explain the eclipse of the moon.

When the moon passes through the cone of shadow behind the earth, light from the sun can no longer reach the moon, which causes a lunar eclipse.

Explain the eclipse of the sun.

When the orbit of the moon passes directly through the line joining the sun to the Earth, the moons umbra reaches the earths surface over a small region, causing a total solar eclipse.

During the eclipse of a sun, when can a partial eclipse be observed?

It can be observed by people who are in the penumbra.

When an object is placed Infront of a pinhole camera, what is formed?

an inverted image

Why is a focused, real, inverted image always produced when an object is placed infront of a pinhole camera?

Because light travels in a straight line, rays from any point on the object have only one possible path into the box, and consequently only one point at which they meet the screen.

(Pinhole camera question) When increasing the distance of the object from the box, what happens and why?

The image becomes smaller because the rays enter at a smaller angle.

(Pinhole camera question) Why does the image become larger on increasing the depth of the box?

Because the rays spread more before reaching the screen?

(Pinhole camera question) If the hole in the front face is made larger, what will the image become?

Blurred due to the formation of several overlapping images and brighter due to the increased light intensity entering the box.

What are the characteristics of the image formed in a plane mirror?

Same size as object
Same distance perpendicularly behind the mirror as the object is in front
Virtual
Laterally inverted

What does virtual mean?

Virtual means not real, as in the image cannot be formed on a screen, and light does not come from where the image appears to be.

What does laterally inverted mean?

This means reversed from side to side, so that the image of a word placed to face a mirror is reversed.

When light enters a second medium perpendicular to its interface, what happens?

It does not deviate, the angles of incidence and refraction are both zero.
Its speed is greater in the less optically dense medium.

When light enters a more optically dense medium other than perpendicularly, what happens?

It refracts towards the normal, and its speed decreases.

When light enters a less optically dense medium other than perpendicularly, what happens?

It refracts away from the normal, and its speed increases.

What are the conditions necessary for total internal reflection?

The angle of incidence must be greater than the critical angle
The ray must be travelling from a more dense medium to a less dense medium (one in which its speed is less)

Explain how a mirage functions

During the day, the temperature of the air above the surface of a road increases due to conduction of heat from the asphalt. A ray of light from low in the sky will refract away from the normal as it enters the hotter, less dense air. The deviation will continue until the ray is totally reflected just above the road. It is then continuously refracted towards the normal as it enters the cooler, denser, air above. An observer receiving this ray will see a virtual image of the sky and may think it is a pool of water.

Explain what you would see when viewing a light source from above a water surface.

When viewing from above, one would see the light leaving the water from within a circle of a certain diameter, d. Rays reaching the surface outside of this circle will be totally internally reflected, because their angle of incidence are greater than the critical angle.

What are some applications of total internal reflection?

Optical fibres, reflecting prisms

Explain how a optical fibre functions.

An optical fibre functions by allowing light to enter through one end of a thin, transparent glass fibre, and then the light is totally internally reflected until it emerges from the other end.

How is the optical fibre protected?

A cladding of different type of glass is placed around the core to protect it.

For total internal reflection to happen, how is the cladding and the core related?

The refractive index of the cladding must be less than that of the core

What are the uses of optical fibres?

Telecommunications and endoscopes.

Explain telecommunications.

Electronic communications for cable TV, telephone and the internet are transmitted by means of light pulses in fibre-optic cables.

Explain endoscopes.

These are used for diagnostic imaging and theraphy.

Explain diagnostic imaging.

Light is transmitted into the patient through a bundle of optical fibres. The reflected light then returns through another bundle of fibres connected to a video camera which displays the image on a screen.

Explain endoscope therapy.

Tumours in solid organs are difficult to remove by surgery, so a laser beam is directed to destroy such tumors by means of optical fibres.

Explain reflecting prisms

Total internal reflection is utilized in optical devices, allowing 100% of the radiation to be reflected to produce a stronger image.