Physics P1

1.1 Infrared radiation

• Infrared radiation is energy transfer by electromagnetic waves
• all objects emit infrared radiation.
• the hotter an object is the more infrared radiation it emits in a given time.

1.2 Surfaces and radiation

• dark,matt surfaces emit infrared radiation more quickly than light, shiny surfaces.
• dark,matt surfaces absorb infrared radiation more quickly than light, shiny sirfaces.
• light, shiny surfaces reflect more infrared radiation than dark, matt surfaces.

1.3 States of matter

• flow, shape, volume and density are the properties used to describe each state of matter.
• the particles in a solid are held next to each other, vibrating in their fixed positions.
• the particles in a liquid move about at random and are in contact with each other.
• the particles in a gas move about randomly and are much farther apart than particles in a solid or liquid.

1.4 Conduction

• metals are the best conductors.
• materials such as wool and fibreglass are good insulators.
• conduction in a metal is mainly due to free electrons transferring energy inside the metal.
• non-metals are poor conductors because they do not contain free electrons.

1.5 Convection

• convection is the circulation of a fluid (liquid or gas) caused by heating it.
• convection takes place only in liquids and gases (fluids).
• heating a liquid or a gas makes it less dense so it rises and causes circulation.

1.6 Evaporation and condensation

• evaporation is when a liquid turns into a gas.
• condensation is when a gas turns into a liquid.

1.7 Energy transfer by design

• the rate of energy transfer 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 surrounding

1.8 Specific heat capacity

• the greater the mass of an object, the more slowly its temperature increases when it is heated.
• the rate of temperature change in a substance when heated depends on the energy transferred to it, its mass and its specific heat capacity.

1.9 Heating and insulating buildings

• the rate of energy transfer to or from our homes can be reduced.
• U-valves tell us how much energy per second passes through different materials. The lower the U-valve the better the material is as an insulator.
• solar heating panels do not use fuel to heat water but they are expensive to buy and install.

2.1 Forms of energy

• energy exists in different forms.
• energy can be transferred from one form into another form.
• when an object falls and gains speed, its gravitational potential energy decreases and its kinetic energy increases.

2.2 Conservation of energy

• energy can be trasferred from one form to another, or from one place to another.
• energy cannot be created or destroyed.
• conservation of energy applies to all energy changes.

2.3 Useful energy

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

2.4 Energy and efficiency

• the fficiency of an appliance = useful energy transferred by the appliance / total energy supplied to the appliance (x100%)
• no machine can be more than 100% efficient
• measures to make machines more efficient include reducing:

-friction

-air resitance

-electrical resistance

-noise due to vibrations

3.1 Electrical appliances

• electrical appliances can transfer electrical energy into useful energy at the flick of a switch
• uses of everyday electrical appliances include heating, lighting, making objects move and creating sound and visual images
• an electrical appliance is designed for a particular purpose and should waste as little energy as possible

3.2 Electrical power

• power is rate of transfer of energy
• P=E/t
• Efficiency = useful power out/total power in (x100%)

3.3 Using electrical energy

• the kilowatt-hour is the energy supplied to a 1kW appliance in 1 hour
• E= P x t
• Total cost = number of kWh x cost per kWh

3.4 Cost effectiveness matters

• cost effectiveness means getting the best value for money
• to compare the cost effectiveness of different appliances, we need to take acount of a number of different costs

4.1 Fuel for electricity

• electricity generators in power stations are driven by turbines
• coal,oil and natural gas are burned in fossil-fuel power stations
• uranium or plutonium is used as the fuel in a nuclear power station
• biofuels are renewable sources of energy which can generate electricity

4.2 Energy from wind and water

• a wind turbine is an electricity generator on top of a tall tower
• waves generate electricty by turning a floating generator
• hydroelectricty generators ar turned by warer running downhill
• a tidal power station traps each high tide and uses it to turn generators

4.3 Power from the Sun and the Earth

• solar cells transfer solar energy directly into electricty
• solar heating panels use the Sun's energy to heat water directly
• geothermal energy comes from inside the Earth

4.4 Energy and the environment

• burning fossil fuels produces greenhouse gases that cause global warming
• nuclear fuels produce radioactive waste
• using renewable energy resources can affect plant and animal life

4.5 The National Grid

• the National Grid distributes electricty from power stations to oyr homes
• step-up and step-down transformers are used in the National Grid
• a high grid voltage reduces energy wastage and makes the system more efficient

4.6 Big energy issues

• gas-fired power stations and pumped storage stations can meet variaions in demand
• nuclear, oil and coal power station can meet base-load demand
• nuclear power stations, fossil-fuel power stations using carbon capture and renewable energy are all likely to contribute to future energy supplies

5.1 The nature of waves

• we use waves to transfer energy and to transfer information
• transverse waves vibrate at right angles to the direction of energy transfer. All electromagnetic waves are transverse waves
• longitudinal waves vibrate parallel to the direction of energy. A sound wave is a longitudinal wave
• mechanical waves, which need a medium (substance) to travel though, may be transverse or longitudinal waves

5.2 Measuring waves

• for any wave, its amplitude is the height of the wave crest or the depth of the wave trough, from the position at rest
• for any wave, its frequency is the number of wave crests passing a point in one second
• 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
• v = f x ^

5.3 Wave properties: reflection

• the normal at a point on a surface is a line drawn perpendicular to the surface
• angles are always measured between the light ray and the normal
• the law of reflecion states that: the angle of incidence is equal to he angle of reflection

5.4 Wave properties: refraction

• refraction of light is the change of direction of a light ray when it crosses a boundary between two transparent substances
• if the speed is reduced, refraction is towards th normal ( e.g. air to glass)
• if the speed is increased, refraction is away from the normal (e.g. glass into air)

5.5 Wave properties:diffraction

• diffracion is the spreading out of waves when they pass through a gap or round the edge of an obtacle
• the narrower a gap the greater the diffraction
• if radio waves do not diffract enough when they go over hills, radio and TV reception will be poor

5.6 Sound

• the frequency range of the normal human ear is from about 20Hz to about 20kHz
• sound waves are longitudinal
• sound waves need a medium in which to travel
• reflctions of sound are called echoes

5.7 Musical sounds

• the pitch of a note inceases if the frequency of the sound waves increases
• the loudness of a note depends on the amplitude of the sound waves
• vibrations created in an instrument when it is played produce sound waves

6.1 The electromagnetic spectrum

• the electromagnetic spectrum (in order of increasing wavelength) is: gamma rays, X-rays, ultrviolet, visible, infrared, microwves, radio waves
• v = f x ^ can be used to calculate the frequency or wavelength of electromagnetic waves

6.2 Light, infrared, microwaves and radio waves

• white light contains all the colours of the spectrum
• visible light, infrared radiation, microwaves and radio waves are all used for communication.

6.3 communications

• radio waves of different frequencies are used for different purposes
• microwaves are used for satellite TV signals
• research is needed to evaluate whether or not mobile phones are safe to use
• optical fibres are very thin fibres that are used to transmit signals by light and infrared radiation

6.4 The expanding universe

• light from distant galaxies is red-shifted
• red-shift provides evidence that the universe is expanding

6.5 The big bang

• the universe started with the Big Bang: a massive explosion from a very small initial point.
• the universe has been expanding ever since the Big Bang
• cosmic microwave background radiation (CMBR) is electromagnetic radiation created just after the Big Bang
• at present CMBR can only be xplained by the Big Bang theory

1.1 Distance-time graphs

• the gradient of the line on a distance-time graph represents an object's speed
• the steeper the line on a distance-time graph, the greater the speed it represents
• speed (m/s) = distnace travelled (m) /time taken (s)

1.2 Velocity and acceleration

• velocity is speed in a given difection
• accelration is the change of velocity per second a = v-u /t

1.3 More about velocity-time graphs

• if the line on a velocity-time graph is horizontal, the acceleration is zero
• the gradient of a velocity-time graph represents acceleration
• the area under the line on a velocity-time graph is the distance travelled

1.4 Using graphs

• the speed of an object is given by the gradient of the line on its distance-time graph
• the accelaeration of an object is given by the gradient of the line on its velocity-time graph
• the distance travelled by an object is given by the area under the line of its velocity-time graph

2.1 Forces between objects

• a force can change the shape of an object or change its motion or state of rest
• th uni of orce is the newton (N)
• when two objects interact they always exert equal and opposite forces on each other

2.2 Resultant force

• the resultant force is a single force that has the same effect as all the forces acting on an object
• if an object is accelerating there must be a resultant force acting on it

2.3 Force and acceleration

• the bigger the resultant force on an object, the greater its acceleration
• the greater the mass of an object, the smaller its acceleration for a given force.
• F = m x a

2.4 On the road

• friction and air resistance oppose the driving force of a car
• the stopping distance of a car depends on the thinking distance and the braking distance

2.5 Falling objects

• the weight of an object is the force of gravity on it. Its mass is the quantity of matter in it
• an objet acted on only by gravity accelerates at about 10 m/s^2
• the terminal velocity of a falling object is the velocity it reaches when it is falling in a fluid. The weight is then equal to the drag force on the object.

2.6 Stretching and squashing

• The extension is the difference bewteen the lenth of the spring and it original length
• the extension of a spring is directly proportional to the force applied to it, provided the limit of proportionality is not exceeded
• the spring constant of a spring is the force per unit extension needed to stretch it

2.7 Force and speed isues

• fuel economy of road vehicles can be improved by reducing the speed or fitting a wind deflector
• average speed cameras are linked in pairs and they measure the average speed of a vehicle
• anti-skid surfaces increase the friction between a car tyre and the road surface. This reduces skids, or even prevents skid altogether.

3.1 Energy and work

• work is done on an object when a force makes the object move
• energy transferred = work done
• W = F x d
• work done to overcome friction is transferred as energy that heats the object that rub together and the surroundings

3.2 Gravitational potential energy

• the gravitational potential energy of an object depends on its weight and how far it moves vertically
• Ep = m x g x h

3.3 Kinetic energy

• the kinetic energy of a moving object depends on its mass and it speed
• Ek = 1/2 x m x v^2
• elastic potential energy is the energy stored in an elastic object when work is done on the object

3.4 Momentum

• p = m x v
• the unit of momentum is kg m/s
• momentum is conserved whenever objects interact, provided no external forces act on them

3.5 Explosions

• momentum = mass x velocity; and velocity is speed in a certain direction
• when two objects push each other apart, they move apart:

- with different speeds if they have unequal masses

- with equal and opposite momentum so their total momentum is zero

3.6 Impact forces

• when vehicles collide, the force of the impact dpends on mass, change of velocity and the duration of the impact
• when two vehicles collide:

- they exert equal and opposite forces on each other

- their total momentum is unchanged

3.7 Car safety

• Seat belts and air bags spread the force across the chest and they also increase the impact time
• side impact bars and crumple zones "give way" in an impact so increasing the impact ime
• we can use the conservation of momentum to find the speed of a car before an impact

4.1 Electrical charges

• certain insulating materials become charged when rubbed together
• electrons are transferred when objects become charged
• like charges repel; unlike charges attract

4.2 Electric circuits

• every component has its own agreed symbol
•  I = Q/t

4.3 Resistance

• V = W/Q = E/Q
• R = V/I
• Ohm's law states that the current through a resistor at constant temperature is directly proportional to the potential difference across the resistor
• reversing the current through a component reverses the potential difference across it

4.4 More current-potential difference graphs

• filament bulb: resistance increases wih increase of the filament temperature
• diode: "forward" resistance low; "reverse" resistance high
• thermistor: resistance decreases if its temperature increases
• LDR: resistance decreases if the light intensity on it increases

4.5 Series circuits

• for component in series:

- the current is the same in each component

- adding the potential differences gives the total potential difference

- adding the resistances gives the toal resistance

4.6 Parallel circuits

• for components in parallel

- the total current is the sum of the currents through the separate components

- the bigger the resistance of a component the smaller the current is

• in a parallel circuit the potential difference is the same across each component
• to calculate the current through a resistor in a parallel circuit use I = V/R