Chapter Text
Specific heat capacity is the amount of energy required to raise the temperature
Of one kilogram of a substance by 1 degree.
In a closed system there is no net (overall) change in energy since energy cant
Be created or destroyed, only transfered/stored/dissipated.
Reducing unwanted energy transfers can make a system more efficient, this can
Be done through lubrication and thermal insulation to reduce useful energy from
Being wasted.
In a building the cooling that takes place is dependent on the thickness/thermal
Conductivity of the walls.
Renewable energy gets replenished faster than it is used up.
Main energy resources are:fossil fuels(coal,oil,gas),nucelar fuel,bio fuel wind ect…
Electrical charge cant flow if the circuit isnt closed and doesnt contain a source of
Potential difference.
Current is rate of flow of charge, size of current is dependant on rate of flow of charge.
Current is the same everywhere in a closed series circuit.
Larger current leads to more resistance so step up transformers decrease current
And increase voltage to reduce resistance.
Current in a fixed resistor is directly proportional to potential difference/linear graph.
Current in filament lamps increases non linearly as the potential difference also increases due to loss of current due to thermal energy loss.
Diodes only allow potential difference in one direction and have very high resistance in one direction and very low resistance on the other side.
Resistance in a thermistor decreases as temperature increases.
Resistance in an LDR (light dependant resistor) decreases as light intensity increases.
In a series circuit:same current everywhere,potential difference of power supply is equal to total potential difference of all components,total resistance of 2 components is the sum of the resistance of all components.
In parallel circuits:potential difference across each component is the same, total resistance of all components is less then resistance of smallest resistance component.
1/total resistance = 1/component 1’s resistance + 1/components 2’s resistance ect…
Adding more resistors in a parallel circuit decreases the total resistance since the electricity has more less resistant paths to take since electricty takes the path of least resistance.
Series dc circuits are useful for testing since ameters and voltmeters can be more easily attached
Ac is when there is a changing potential difference difference dirrection, the rate the potential difference changes direction(frequency) is measured in hertz, the hertz of the national grid is 50 hz at 230volts.
In a power plug there are 3 wires:brown=live(carries 230v and connected to fuse)
Neutral=blue(completes circuit ),earth=green/yellow(only carries current in case of a fault).
Carrying a conection between live and earth is very dangerous.
Energy transfer is dependant on time that it is used.
Work is done when a charge flows in a circuit.
National grid is a system of cables and transformers connecting power stations to the consumers home.
National grid is the efficient way to transfer energy since transformers allow for less energy loss due to thermal energy.
Step up transformer=increased voltage/decreased current/decreased resistance
Step down transformers = decreased voltage/increase current
Step down transformers allow power to safely transfer to consumers house.
During state changes the mass stays the same and so does the temperature as energy is supplied to the substance.
Changing states is a physical process not chemical as no new substances are made and the material can recover its properties if the change is reversed.
Total energy in a system by the particles is called the internal energy.
Internal energy is the amount of kinetic + potential energy of all of the particles in the system.
Heating increases energy of the particles in a system leading to a higher temperature or a change of state, changing states raises internal potential energy but does not increase temperature/kinetic energy.
Kinetic energy is the same as temperature as the warmer a particle is the faster it vibrates due to more kinetic energy.
Specific latent heat of vaporisation = changing state liquid → vapour.
Temperature of gas is proportional to kinetic energy of particles.
Increased temperature of gas = increased pressure exerted by a gas
If volume of a container is decreased the molecules hit the walls more often resulting in an increase frequency of collisions with the walls resulting in more pressure exerted.
Electrons are arranged at different energy levels from the nucleus.
Absorption of electromagnetic radiation leads to electrons moving further from nucelus/going to a higher energy level.
Electromagnetic radiation can also be emitted causing to electrons to move closer to the nucelus due to moving to a lower energy level.
Electron amount = Proton amount, this is because atoms have no electrical charge.
Protons+nuetrons= mass number.
Atoms with a different number of nuetrons are called isotopes.
Alpha particles = 2 nuetrons + 2 protons / helium nucleus
Beta = high speed electron(nuetron becomes electron and proton, electron is omitted from nucleus)
Gamma = electromagnetic radiation .
Beta decay does not change mass but does change charge, this is because electrons have a very small mass compared to nuetrons/protons.
Radioactive decay is a random process,cant be sped up/slowed down or predicted.
Half life is the time taken for the rate of radioactive decay to halve from its initial level.
Irradiated substances are when they are exposed to radiation but they do not become radioactive, irradiation can be used to kill pathogens and cancer cells.
Contaminated substances have touched a radioactive sample and have become radioactive as some radioactive particles stay on the surface of the contaminated sample.
Scaler quantities only have magnitude and no direction eg:velocity/mass/temperture.
Magnitude is the “size” of the force eg: 5KG has a smaller magnitude than 10KG.
Vector quantitiesare represented by an arrow and show magnitude and direction,the size of the arrow represents magnitude and direction of the arrow shows direction of the force.
Forces are either pull/push and contact/non contact
Weight is dependant on gravitational field strength but mass is a constant, eg:weight on the moon is less then on earth but the mass is the same in both.
Weight and mass are directly proportional, weight canbe measured with a newtometer.
All forces acting on an object can be called one overall force called resultant force
Speed og walking is not a good measure since it is dependant on many factors:age,terrain,fittness ect… and therefore is rarely constant.
Speed of sound in air is about 330 m/s
Velocity is a vector quantity as speed is a scalar quantity.
Area under a velocity time graph is the distance traveled.
Any object falling under gravity has an acceleration of 9.8 m/s^2
Any object falling in a fluid will accelerate then the resultant force will be 0 and the object will move at terminal velocity.
Newtons first law” If resultant force is 0:
Stationary object=stay stationary
moving object=move at same speed and wont accelerate”
When a vehicle travels at a constant speed the resultant force is 0 because the resistive forces are equal to the driving force.
Objects resistance of staying in the state of rest or in movment is called inertia
Newtons second law”acceleration is proprtional to resultant force:FORCE=MASS X ACCELERATION”
Inertial mass is how difficult it is to change velocity of an object.
Newtons third law”When 2 objects interact an equal and opposite force is exerted”
Stopping distance = thinking distance + braking distance.
Higher speed = higher braking force/distance.
Typical reaction time is from 0.2 seconds to 0.9 seconds
Reaction time can be impaired due to tiredness,drugs and alcohol.
Braking distance can be effected due to weather conditions,condition of vehicle ect..
When a force is applied to the brakes workdone by friction force on the brakes reduces kinetic energy slowing down the car heating up the brakes.
Larger braking force can lead to brakes overheating or loss of control of the vehicle.
Momentum = mass x velocity
In a closed system the momentum before the collsion/incident is equal to momentum after the collision since energy is transferred from one object to the other.
Waves are either transverse or longitudinal.
Transverse waves move perpendicular to direction of the wave
Longitudinal waves move parallel to the the direction of waves
Sound waves are longitudinal
Ripples in water are transverse waves.
For ripples in water its the wave not the water that moves since if you place a ball on the water it moves up and down but not in the direction of the wave, therefore the medium that the wave travels through is not moving but the wave is.
Amplitude is the the distance from the centre of the wave/the direction of travel of the wave.
Wavelength is the distance from one poin to the next equivalent point.
frequency is the number of waves passing through a point per second.
All waves transfer energy.
Wavespeed is the rate of energy transfer.
Our eyes can only detect visible light in the electromagnetic spectrum.
All electromagnetic waves travel at the same velocity in a vacuum.
Waves are ordered in the spectrum for long to short wavelength/low to high frequency.
Different substances can transmit/aborb electromagnetic waves differently.
Refraction happens due to change in speeds of waves when entering a different density medium causing a turning force.
Radio waves are produced by oscillations in electrical circuits.
When radio waves are absorbed they can form an alternating current with the same frequency as the radio wave.
Changes in atoms can cause electromagnetic waves to be absorbed or transmitted
Gamma rays are produced due to changes in the nucleus of the atom.
UV waves cause skin to age faster and increase risk of skin cancer.
X ray and gamma can mutate genes and cause cancer.
Uses of waves:
radio=radios
microwaves=microwaves
infrared=cooking food
Visible light=fibre optic
uv=tanning beds
xrays/gamma rays = medical treatment/diagnostic equipment
Magnetic poles on earth are NOT the same as geographical poles
Poles on a magnet are where the magnetic forces are strongest.
2 same poles reppel, two opposite poles attract.
A permanant magnet has its own magnetic field.
An induce magnet only has a magnetic field when placed inside another magnetic field(aka when a current is ran through a wire wrapped around it)
Region around a magnet where a force is acted is called its magnetic field.
Magnets must be made for either:steel iron cobal or nickel.
Magnet + magnetic material = always attraction.
Earth has a magnetic core since magnetic compasses can point to the north and south magnetic poles.
When a current flows a magnetic field is produced around the wire.
Wrapping a wire with a current through it can form a solenoid, you can increase strength of the solenoid through adding a soft iron core and increasing the current.
When a conductor is placed in a magnetic field from the wire a force is exerted, this is called the motor effect and the direction of force can be found with flemings left hand rule.
Coil of wire with a current in a magnetic field rotates, this is how electric motors work.