Physics - Unit 1

1. We use waves to transfer energy and transfer information
2. Transverse waves vibrate at right angles to the direction of energy transfer of the waves. All electromagnetic waves are transverse waves
3. Longitudinal waves vibrate parallel to the direction of energy transfer of the waves. A sound wave is an example of a longitudinal wave
4. Mechanical waves, which need a medium (substance) to travel through, may be transverse or longitudinal waves

1. For any wave, its amplitude is the height of the wave crest or the depth of the wave trough from the position at rest
2. For any wave, its frequency is the number of wave crests passing a point in one second
3. For any wave, its wavelength is the distance from one wave crest to the next wave crest. This is the same as the distance from one wave trough to the next wave trough
4. v = f x λ wave speed = frequency x wavelength

1. The normal at a point on a mirror is a line drawn perpendicular to the mirror
2. The law of reflection states that: the angle of incidence = the angle of reflection
3. For a light ray reflected by a plane mirror: 1 The angle of incidence is the angle between the incident ray and the normal. 2 The angle of reflection is the angle between the reflected ray and the normal

1. Refraction is the change of direction of waves when they travel across a boundary
2. When a light ray refracts as it travels from air into glass, the angle of refraction is less than the angle of incidence
3. When a light ray refracts as it travels from glass into air, the angle of refraction is more than the angle of incidence

1. Diffraction is the spreading out of waves when they pass through a gap or round the edge of an obstacle
2. The narrower the gap is, the greater the diffraction is
3. If radio waves do not diffract enough when they go over hills, radio and TV reception will be poor

1. The frequency range of the normal human ear is from about 20 Hz to about 20,000 Hz
2. Sound waves are vibrations that travel through a medium (substance). They cannot travel through a vacuum (as in space)
3. Echoes are due to sound waves reflected from a smooth, hard surface

1. The pitch of a note increases if the frequency of the sound waves increases
2. The loudness of a note increases if the amplitude of the sound waves increases
3. Vibrations created in an instrument when it is played produce sound waves

Anotações:

• Sound energy Infrared energy Chemical energy Kinetic energy Heat energy Elastic energy Nuclear energy Light energy Electrical energy Gravitational potential energy

1. Energy exists in different forms
2. Energy can change from one form to another
3. Remember the forms of energy with the acroynm SICK HEN LEG
4. When an object falls and gains speed, its gravitational potential energy decreases and its kinetic energy increases

1. Energy cannot be created or destroyed, it can only changes form
2. The conservation of energy applies to all energy changes

1. Useful energy is energy in the place we want it and in the form we need it
2. Wasted energy is energy that is not useful
3. Useful energy and wasted energy both end up being transferred to the surroundings, which become warmer
4. As energy spreads out, it gets more and more difficult to use for further energy transfers

1. The efficiency of a device = useful energy transferred by the device ÷ total energy supplied to the device (x 100%)
2. No machine can be more than 100% efficient
3. Measures to make machines more efficient include reducing friction, air resistance, electrical resistance and noise due to vibrations

1. Electricity generators in power stations are driven by turbines
2. Coal, oil and natural gas are burned in fossil fuel power stations
3. Uranium or plutoium are used as the fuel in a nuclear power station. Much more energy is released per kg from uranium or plutonium than from fossil fuels
4. Biofuels are renewable sources of energy. Biofuels such as methane and ethanol can be used to generate electricity

1. A wind turbine is an electricity generator on top of a tall tower
2. Waves generate electricity by turning a floating generator
3. Hydroelectricity generators are turned by water running downhill
4. A tidal power station traps each high tide and uses it to turn generators

1. Solar cells are flat solid cells that convert solar energy directly into electricity
2. Solar heating panels use the Sun's energy to heat water directly
3. Geothermal energy comes from the energy realeased by radioactive substances deep inside the Earth
4. Water pumped into hot rocks underground produces steam to drive turbines that generate electricity

1. Fossil fuels produce increased levels of greenhouse gases which could cause gloabal warming
2. Nuclear fuels produce radioactive waste
3. Renewable energy resources can affect plant and animal life

1. The National Grid is a network of cables and transformers that distributes electricity to our homes from distant power stations and renewable energy generators
2. Step-up transformers are used to step up power station voltages to the grid voltage. Step-down transformers are used to stepd the grid voltage down for use in homes
3. A high grid voltage reduces energy loss and makes the system more efficient

1. Gas-fired power stations and pumped-storage stations can meet variations in demand
2. Nuclear, coal and oil power stations can meet base-load demand
3. Nuclear power stations, fossil-fuel power stations using carbon capture and renewable energy are all likely to contribute to future energy supplies

1. Electrical appliances can transfer electrical energy into useful energy at the flick of a switch
2. Uses of everyday electrical appliances include heating, lighting, making objects move (using an electric motor), creating sound and creating visual images
3. An electrical appliance is designed for a particular purpose and should waste as little energy as possible

1. Power is a rate of transfer of energy
2. Power = energy transferred ÷ time
3. In this equation power is in watts (W), energy transferred is in joules (J) and time is in seconds (s)

1. The kilowatt-hour is the energy supplied to a 1kW appliance in 1 hour
2. Total cost = number of kWh used x cost per kWh

1. Cost effectiveness means getting the best value for money
2. To compare the cost effectiveness of different appliances, we need to take account of costs to buy it, running costs and other costs such as environmental costs

1. The electromagnetic spectrum (in order of decreasing wavelength, increasing frequency and energy) is: - radio waves, - microwaves, - infrared radiation, - light, - ultraviolet radiation, - gamma radiation and x-rays
2. The wave speed equation is used to calculate the frequency or the wavelength of electromagnetic waves

1. White light contains all the colours of the visible spectrum
2. Infrared radiation is used for carrying signals from remote handsets and inside optical fibres
3. We use microwaves to carry satellite TV programmes and mobile phone calls.
4. Radio waves are used for radio and TV broadcasting, radio communications and mobile phone calls
5. Different types of electromagnetic radiation are hazardous in different ways. Microwaves and radio waves can cause internal heating. Infrared radiation can cause skin burns

1. Radio waves of different frequencies are used for different purposes because the wavelength (and therefore frequency) of waves affects: - how far they can go, - how much they spread, - how much information they can carry
2. Microwaves are used for satellite TV signals
3. Further research is needed to evaluate whether or not mobile phones are safe to use
4. Optical fibres are very thin transparent fibres that are used to transmit signals by light and infrared radiation

1. The doppler effect is the change in observed wavelength (and frequency) of waves due to the motion of the source of the waves
2. The red-shift of a distant galaxy is the shift to longer wavelengths of the light from it because the galaxy is moving away from us
3. The faster a distant galaxy is moving away from us, the greater its red-shift is
4. All the distant galaxies show a red-shift. The further away a distant galaxy is from us, the greater its red-shift is
5. The distant galaxies are all moving away from us because the universe is expanding

1. The universe started with the Big Bang, a massive explosion from a very small point
2. The universe has been expanding ever since the Big Bang
3. Cosmic microwave background radiation (CMBR) is electromagnetic radiation created just after the Big Bang
4. CMBR can only be explained by the Big Bang theory

1. Infrared radiation is energy transfer by electromagnetic waves.
2. All object emit infrared radiation
3. The hotter an object is, the more infrared radiation it emits in a given time

1. Dark, matt surfaces emit more radiation than light, shiny surfaces
2. Dark, matt surfaces absorb more infrared radiation than light, shiny surfaces
3. Light, shiny surfaces reflect more infrared radiation than dark, matt surfaces

1. Flow, shape, volume and density are the properties used to describe each state of matter
2. The particles in a solid are held together in fixed positions
3. The particles in a liquid move about at random and are in contact with each other
4. The particles in a gas move about randomly and are much further apart than particles in a solid or liquid

1. Metals are the best conductors of energy
2. Materials such as wood and fibreglass are the best insulators
3. Conduction of energy in a metal is due mainly to free electrons transferring energy inside the metal
4. Non-metals are poor conductors because they do not contain free electrons

1. Convection is the circlation of a fluid (liquid or gas) caused by heating it
2. Convection takes place only in liquids and gases
3. Heating a liquid or a gas makes it less dense so it rises and causes circulation

1. Evaporation is when a liquid turns into a gas
2. Condensation is when a gas turns into a liquid
3. Cooling by evaporation of a liquid is due to faster moving molecules escaping from the liquid
4. Evaporation can be increased by increasing the surface area of the liquid, by increasing the liquid's temperature, or by creating a draught of air across the liquid's surface
5. Condensation on a surface can be increased by increasing the area of the surface or reducing the temperature of the surface

1. The rate of energy transferred to or from an object depends on: - the shape, size and type of material of the object - the materials the object is in contact with - the temperature difference between the object and its surroundings.

1. The greater the mass of an object, the more slowly its temperature increases when it is heated
2. The rate of temperature change of a substance when it is heated depends on: the energy supplied to it, its mass and its specific heat capacity
3. Storage heaters use off-peak electricity to store energy in special bricks

1. Energy transfer from our homes can be reduced by fitting: loft insulation, cavity wall insulation, double glazing, draught proofing and aluminium foil behind radiators
2. U-values tell us how much energy per second passes through different materials
3. Solar heating panels do not use fuel to heat water but they are expensive to buy and install