SoundSUBTITLE

What is Sound?• Sound is produced when something vibrates, which means it moves back and forth very quickly

• When something vibrates, it passes the vibration into its surrounding environment

• The vibration creates regions of space in which the air particles are bunched together, called compressions and regions in which they spread out called rarefactions

• A sound wave is the movement of alternating compressions and rarefactions

Types of Waves

• Transverse wave a wave in which the vibration is at right angles to the direction the wave is travelling

• Longitudinal wave a wave in which the vibration is in the same direction that the wave is travelling

The Speed of Sound

• The more closely packed particles are packed together, the faster a sound wave will travel through it

•As a result, sound travels faster through solids than through liquids, and faster through liquids than gases

Where does Sound Go?• Sound passes through thin walls and is transmitted

short distances through most materials

• Hard surfaces such as concrete or bathroom tiles, reflect sound waves• This reflected sound is known as an echo

• The time difference between sending and receiving sound can be measured e.g. calculating the depth of objects in the sea using sonar

• Soft materials like curtains, carpet and cushions absorb sound and convert it to heat

• Sound absorption like this is needed in concert halls, so there is no overlap between sounds performed and their echoes which would other wise distort what you hear

Frequency and Pitch• Frequency the number of waves passing a point every second

• Hertz the unit to measure frequency

• Wavelength the distance from one peak of a wave to the next, measured in metres

• Louder sounds have larger peaks so louder sounds have greater sounds than softer sounds

• Pitch is the highness or lowness of sound. The pitch that you hear depends on the frequency of the vibrating air

• Our ability to hear higher frequencies of sound reduces as we age • Young people hear a range of frequencies up to 20 000

Hz, yet most people over 65 years cannot hear frequencies above 5000 Hz

• Ultrasound is the name given to sound waves with frequencies above our hearing range e.g. ultrasound in pregnancy

• Infrasound is the rang of sound below our frequencies

The Ear: How you hear• Your ears collect sound waves, amplify their vibrations

and convert these into electrical impulses• Your brain interprets these impulses as sound

• The measurement for sound is the decibel dB

• The sound level above 130 dB can cause pain• Exposed to sound levels of 80 dB long enough can

also cause damage to your ears

• The threshold of hearing is the smallest sound level that can be heard when the air is vibrating at 1000 Hz

The Electromagnetic Spectrum• Electromagnetic spectrum complete range of wavelengths of energy radiated as electric and magnetic fields

• Radio waves include the low-energy waves that are used to communicate over long distances through radio and television, they also include radar and microwaves

• Infra-red radiation invisible to the human eye is emitted by all objects and is sensed as heat. The amount of infrared radiation emitted by an object increases as its temperature increases

• Visible light is necessary for the sense of sight and photosynthesis

• Ultraviolet radiation is invisible to the human eye, it helps the body produce vitamin D, too much causes sunburn

• X-rays have enough energy to pass through human flesh; can be used to kill cancer cells, find weakness in metals. Bones absorb more x-ray energy than sorter tissue

• Gamma rays have more energy than x-rays and also do more damage to living cells

• Electromagnetic waves transmit energy from one place to another

Light

Properties of LightLight hits the surface and

The material is called Examples

Almost all light is transmitted through the substance. A clear image can be seen through it.

Transparent Clear glassShallow water

Some light may be reflected, and light that passes through is scattered. An image seen through it is fuzzy.

Translucent Tissue paperFingernailsFrosted glass

Light is either reflected from or absorbed into the substance, and no light is transmitted. No image can be seen through it.

Opaque A brickA piece of woodA deskA football

The Law of Reflection• According to the law of reflection:

angle of incidence = angle of reflection

Refraction• Refraction is the bending of light as it enters or leaves

different substances

• Light refracts when it travels from one transparent substance into another

Convex Lenses• A lens is a transparent piece of plastic or glass that is

shaped or curved outward or inwards

• A lens that bulges outwards is called a convex lens

• It enlarges the virtual image like a magnifying glass

Concave Lens• A lens that curves inwards is called a concave lens

• A concave lens only produces images that are smaller upright and virtual

The Eye

• Light enters the eye, is refracted by the cornea and focused by the lens which is convex

• The clear upside-down image is formed on the retina at the back of the eye

• This image is converted into a series of electrical signals, which then travel along the optic nerve to the brain for the brain to interpret the information

Vision Problems• Short-sightedness (myopia) can focus on close objects, such as a book, but distant objects such as children in a playground are not clear

• Long-sightedness (hyperopia) can see distant objects clearly but has trouble focusing on close objects. They need to use glasses for reading or doing close work

The Visible Spectrum• Visible spectrum is the range of colours that can be seen by the

eye

• Dispersion splitting of white light into separate colours.

• We see a red apple as being red if it reflects red light towards our eyes; it will absorb yellow green, blue, indigo and violet

• The seven colours are: red, orange, yellow, green, blue, indigo, violet

• Primary colours: red, green and blue

• Secondary colours: magenta, cyan and yellow

• Your eyes have three types of photoreceptor cells called cones. Each type of cone is sensitive to one of the primary colours.

• Combinations of signals from these three types of cells can give us our full colour view of the world

Heat and Electricity

HeatConduction

• Conduction is the transfer of heat through a substance as a result of neighbouring vibrating particles

• By colliding with other particles they transfer some of their energy to other particles

• Most solids are better conductors than liquids and gases because their particles are closer together

• Materials that are poor conductors are called insulators

Convection

• Convection is the transfer of heat through the flow of particles

• Convection current is circular movement that occurs when warmer, less dense fluid particles rise and cooler, denser fluid particles sink

Radiation

• Heat is transferred without the presence of particles as electromagnetic radiation

Electricity• Static electricity is the build up of charge on the surface

• Electrons have rubbed off of one surface and have transferred it to another surface• If a build up of charge continues, electrons may jump

across the gap from the negatively charged surface to the positively charged surface• As they jump back, the electrons release all their

energy in one go into heat, light, sound and motion like a lightening bolt

• Current is the moment of charge• These moving electrons have energy that is

transformed into other forms of energy as the electrons pass through thrings like globes, heating elements and motors

Simple Electric Circuits• Electrons need a path to travel around so they can

deliver their energy called an electric circuit

• An electrical circuit needs 3 things1. An energy source e.g. Battery (power supply)2. An energy war e.g. light globe, motor (load)3. Wires to connect everything (conducting path)

Current and Voltage• Current is a measure of how much electric charge flows through a circuit, the more charge that flows, the bigger the current

• Current is measured in units called amps, the symbol is A

• Voltage is the measure of the difference in electrical energy between two parts of a circuit, the bigger the difference in energy, the bigger the voltage

• Voltage is measure in units called volts, the symbol is V

Series and Parallel Circuits• In a series circuit all the components of the circuit are

connected up one after another to form a single loop

• In this type of circuit there is only one path for the current to flow

• A parallel circuit has a number of branches where each branch has its own components

• Each bulb glows as brightly as if it was the only bulb in the circuit

• If you disconnect on bulb the other still glows, because the current still flows through the unbroken branch of the circuit

Using an Ammeter•An ammeter is used to measure the size of electric current flowing in an electric circuit

• It measures the electric current in amperes

• It is connected in series with the circuit

Using a Voltmeter

•A voltmeter is used to measure the voltage gain across the terminals of a power supply or voltage drop across parts of an electric circuit

• It is measured in volts

• It is connected in parallel to the circuit

Resistance• How much current flows in a circuit is determined by the

resistance of the circuit

• The electrical resistance of a material is a measure of how difficult it is for charged particles to move through it

• Most connecting wires have very low resistance and hardly any energy lost by the electrons

• Resistors are devices that are placed deliberately in circuits to control or reduce the size of the current

• Resistance is measured in units called Ohms Ώ

• The relationship between voltage, current and resistance is known as Ohm’s Law