Waves, light and sound Flashcards by Malak Hamidh

Define a wave

A disturbance or oscillation that travels through space and matter accompanied by the transfer of energy

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What is propagation of wave?

Direction in which waves travel

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What are transverse waves

Vibrations of the particles are perpendicular to the direction in which energy transfer

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Examples of transverse waves

Water waves seismic waves electromagnetic waves

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What are longitudinal waves?

Vibrations of the particles are parallel to the direction in which energy transfer

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Give examples of longitudinal waves

Sound waves and earthquake waves

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What do longitudinal waves have?

Compressions and rarefactions

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What is the wavelength?

Distance between two successive equivalent points.

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What is frequency?

Number of waves per unit time- Hertz Hz

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What is the equation for frequency?

F- number of waves/time

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What is a period?

The time taken for one complete oscillation

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What is the equation for a period?

Time/ number of waves

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What is the amplitude?

The maximum displacement from the horizontal axis to the peak

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Equation for speed of sound

Wave speed= Frequency * Wavelength

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What is a ray?

Direction of travel- perpendicular to wave fronts

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What is a wave front?

Surface over which an optical wave has a constant phase

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What do circular waves have?

Circular wave fronts

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What do plane waves have?

Plane wave fronts

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What does the pitch depend on?

The frequency of the source of sound

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What does a high frequency produce?

High pitch noise

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What does a large amplitude produce?

A louder sound

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What type of wave is a light wave?

Transverse waves

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What is the speed of light?

3 * 10^8 m/s

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Where does light travel faster?

In low dense media

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What type of wave in a sound wave?

Longitudinal

Where does sound travel fastest?

In denser media

What is the speed of sound in air?

330 m/s

What is the speed of sound in water?

1500 m/s

What is the speed of sound in solid?

5000 m/s

How does light travel?

In straight lines

Give the three different wave effects

Reflection, Diffraction and Refraction

What happens to light waves when they enter a dense medium?

Bend towards the normal

What happens to sound waves when they enter a dense medium?

Bend away from the normal

What is the range of human hearing?

Between 20Hz and 20 kHz

What is an ultrasound?

Frequencies with above 20kHz

What are luminous objects?

Emit their own light

What are non-luminous objects?

They bounce off the light or they reflect the light so we can see them

What is monochromatic light?

Waves that have a single frequency

When does reflection of light happen?

When the light meets a boundary like a mirror, paper and surface of water

What is the normal ray?

It is a virtual line that is perpendicular to the surface at the point of incidence

What is the incident angle?

Angle between normal and incident ray

What is the reflected ray?

Angle between the normal and reflected ray

What are the laws of reflection?

Angle of incidence= Angle of reflection | Incident wave, reflected wave and the normal lie in the same plane

What will happen to the wavelength, frequency and the speed after the reflection?

Nothing will change

What is the image produced from reflection?

Same size, up right down, literally inverted, and virtual

How can we distinguish an echo?

0.1 s

How are good echo produced?

1. The distance between the reflector and the sound source is more than 30 meters. 2. The area of a reflector is large compared to the wavelength of the incident sound 3. The incident sound is high pitched

What do we use echo for?

To survey the depth and nature of the seabed

What is refraction?

When waves enters from one medium to the other medium, it changes its direction depending upon the angle of incidence because of the change in speed

What happens when a ray of light travels from a dense medium to a less dense medium?

Its speed and wavelength increases and the ray bends away

What happens when white light enters a prism?

Red is deviated bent off course least by prism- violet light is deviated most

What is the order of the colours in the spectrum?

``` Red Orange Yellow Green Blue Indigo Violet ```

Give the refractive index equation

Speed of light in air/speed of light in medium

What is snell's law?

n1 sin θ1= n2 sinθ2

What are the conditions of total internal reflection?

The light must travel from denser to to less dense | Its incident angle more than critical angle

What is the critical angle equation ?

Sinθ= 1/n

What is an optical fibre?

A thin rod of high quality glass and very little light is absorbed by the glass

What method does the optical fibre use?

Undergoes repeated total internal reflection even when the fibre is bent

Where are optical fibres used?

Used in endoscopes to allow surgeons to see inside their patients and they can carry huge amounts of information as pulses of light.

What is the focal point?

Where parallel light rays converge after the lens

Describe the image formed when an object is very far way from a convex lens 3F.

Image is real, inverted and the image is smaller

Describe the image formed when when an object is two focal points from a convex lens.

Real inverted and smaller

Describe the image formed is between one and two focal lengths from the convex lens.

Real, inverted and larger

Describe what happens when an object is one focal length from a convex lens

The lines do not intersect

Describe the image formed is half focal lengths from the convex lens.

virtual, enlarged upright

What is diffraction?

The spreading out of waves as they pass through a gap or by an obstacle

What does a big gap in the barrier cause?

The disturbances are very small

What does a small gap cause?

The circular disturbances are massive compared to the undisturbed wave front

When does maximum diffraction happen?

When the width of the gap is equal to the wavelength of the waves

How can sound diffract?

Through a doorway or around buildings

What type of sound diffracts the best and why?

Low pitch- because they have a long wave length compared with the width so they spread our more

What happens when ultrasound is diffracted?

There is little spreading which makes sharp focusing of ultrasound easier- good for medical scanning

What are properties of EM waves?

They travel the same speed in a vacuum

What waves are EM waves?

Transverse waves

Give the order of the EM waves

``` Radio Microwaves Infrared Visible light Ultraviolet X-ray Gamma Ray ```

What are radio waves used for?

Amateur FM radio- TV broadcasts

What are microwaves used for?

Mobile phones Heating effect in microwaves TV and communications

What is infrared used for?

Radiant heaters, toasters TV remote controllers Security alarms Optical fibers

What is ultraviolet used for?

Sterilising equipment to kill bacteria

Why is ultraviolet dangerous?

It can cause skin cancer and may damage the retina and cause blindness

What is X-ray used for?

Treat cancer Detect weapons in luggage To take photographs that reveal flaws of metals

What is gamma ray used for?

To take photographs Killing bacteria Treat cancer Sterilizing food and medical equipment