physics paper 2: WAVES

Amplitude: maximum displacement of a point on the wave from the undisturbed place.

Wavelength: distance between same point on two adjacent waves.

Frequency: number of complete waves passing per second. Measured in Hertz.

PERIOD = 1 ÷ FREQUENCY

TRANSVERSE: - Vibrations are perpendicular to energy direction.

- e.g. EM waves

LONGITUDINAL: - Vibrations are parallel to energy direction.

- e.g. Sound waves

WAVE SPEED (m/s) = FREQUENCY (Hz) X WAVE LENGTH (m)

- OSCILLOSCOPE: measures speed of sound.

- STROBE LIGHT: measures speed of water ripples.

1. Use a signal generator to create waves at a set frequency.

2. Use a strobe light to see wave crests.

3. Find average wavelength by measuring distance between 10 wavelengths, then divide by 10.

4. Use equation to calculate speed.

- STRINGS:

1. Adjust the frequency on signal generator, this gives a clear wave.

2. Measure the wavelength using ruler this will give half- wavelengths, then half it.

3. Use equation to calculate speed.

- Waves can be absorbed, transmitted or reflected.

ANGLE OF INCIDENCE = ANGLE OF REFLECTION

Reflection can be SPECULAR or DIFFUSE.

Specular: wave is reflected in a single direction by a smooth surface.

Diffuse: wave is reflected by a rough surface and the rays are scattered in different directions.

EM waves are all transverse.

Radio waves: 1m - 10^4m

Micro waves: 10^-2m

Infra red: 10^-5m

Visible light: 10^-7m

Ultra light: 10^-8m

X- rays: 10^-10m

Gamma rays: 10^-15m

Refraction= when waves change direction at a boundary.

Optical density: How quickly light travels through an object.

- Use transparent materials

1. Place a transparent rectangular box on a paper and trace it.

2. Use a ray box to shine light through one side of the block.

3. Trace the incident ray and mark where the light emerges on the other side of the block.

4. Remove the block and join up the lines.

5. Draw the normal line where the light enters the block.

6. Use a protractor to measure angle between incident and normal, then refracted and normal.

7. Repeat using different materials.

*But remember to keep the incident angle the same.

- Made from oscillating charges.

1. Alternating current produces oscillating charges (electrons).

2. A transmitter creates radio waves.

3. The radio waves are emitted.

4. The receiver absorbs the waves.

5. The receiver produces Alternating current.

Radio waves uses:

* Bluetooth

* TV

* FM radio

Microwaves:

- used by satellites

microwave oven: use different wavelengths from satellites, these are then absorbed by water molecules in food.

Infrared:

- Increase or monitor temperature

- Used in infrared cameras

- Used in electric heaters

Visible light:

- carry data over a long distance     - fibre optic cables

Ultraviolet radiation:

- fluorescence     - UV lamps for artificial suntan

X- Rays:

- Radiographers in hospitals to see bones

Gamma rays:

- Treat people with cancer     - Medical tracers

Low frequency: pass through soft tissues

High frequency: cause lots of damage

UV rays: damage suurface cells which leads to sunburn, increases skin cancer.

X- rays and gamma rays: ionise which causes gene mutation, increasing cancer.

Radiation dose: measure of radiation in sieverts.

Convex lens:

- bulges outwards

- light converges

Concave lens:

- caves inwards

- light diverges

Real image: light from an object comes to form an image on a screen.

Virtual image: rays diverge, so light appears to be coming from a different place.

To describe an image, say:

1. How big it is

2. If it's upright or inverted

3. If it's real or virtual

MAGNIFICATION = IMAGE HEIGHT ÷ OBJECT HEIGHT

- Opaque objects: don't transmit but may absorb some wavelengths and reflect others.

- White objects reflect all wavelengths equally.

- Black objects absorb all wavelengths.

- Colour filter only let through particular wavelengths.

- All objects emit and absorb infrared radiation.

- The hotter the object, the more infrared it radiates in a given time.

- An object that is hotter than its surroundings, emits more radiation and it cools.

1. Boil water and pour into leslie cube.

2. Hold an infrared detector at a set distance and record the IR radiation.

3. Repeat for each face of cube.

4. You'll find that you detect more IR radiation on the matt and black surfaces.

Perfect black body: object which absorbs all radiation.

- Intensity and distribution of wavelengths emitted by an object depends on the objects's temperature.

- On Earth, some radiation is reflected by the atmoshere, clouds and the Earth's surface.

- Some radiation is absorbed by the atmoshere, clouds and surface.

- Radiation is also emitted.

- caused by vibrating objects.

- These vibrations are passed through a series of compressions and rarefractions.

- When sound waves reach the ear, the ear drum vibrates, this causes us to hear the sound.

- humans sound range is 20Hz to 20 KHz.

- sound waves are reflected easily by smooth surfaces, just like echoes.

- sound waves speed up as they enter denser materials.

- sound gets refracted as they enter different mediums.

Ultrasound: mechanical vibrations which produce sound waves beyond the range of human hearing.

- Ultrasound waves get partially reflected.

Uses:

- Medical imaging => scanning of a foetus.

- Industrial imaging => finding flaws in materials.

- Earthquakes and explosions cause seismic waves.

Two types of seismic waves: P waves and S waves

P waves

- londitudinal

- travel faster than S waves

- travel through solids and liquids

S waves

- transverse

- travel through liquids or gases