Defiiniitions Flashcards
Define electromotive force
The electric potential produced by either an electrochemical cell or by changing the magnetic field.
Define magnetic flux
The total magnetic field which passes through a given area.
What are the seven SI units
Mass: kg
Length: m
Time: seconds
Current: Ampere
Temperature: k
Amount of substance: mol
Luminosity: lux
Prefixes of size small to big
Pico -12, nano, -9, micro -6, milli -3, centi 02, deci -1, klio 3 maga 6, giga 9, tera 12.
What is a scalar quantity
A quantity with no direction but a magnitude
What is a vector quantity
Has magnitude and direction
What is a force couple
A couple is a pair of forces of equal size which act parallel to each other but in opposite directions.
They produce a turning force called torque
What is impulse
It is average force x time.
This is = to change of momentum
Newtons first law
Velocity of an object will not change unless a net force acts on it.
Newtons second law
The rate of change of momentum of an object is directly proportional to the net force which acts on the object
Therefore F=Ma and F = dP/dt
Newtons third law
If an object A exerts a force on object B, then object B exerts an equal but opposite force on object A
What makes cars safe
Seat belts: hold perosn in place, stopping them, strech absorbing EK and increase t
Airbags: incrase t act as a cussion
Stopping peron from hitting hard parts of car
Crumple zones: deform absorbing Ek of crash, increase time taken for the car to slow down.
Current deffintion
Change in Q/ change of time
Potential differance
Work done per unit charge W=QV
Work done and EK in circuits
eV = 1/2mV^2
What is I = nAve
I = current
n = number density per M^3
V = mean drift velocity in M/s
e = 1.6x10^-19
A = cross sectional area M^2
Resistivity facts
Measured in ohm meters
If two materials are the same they have the same resistivity no matter what as long as same temperaute
Ohms law
Voltage is directly proportional to current as long as temperature remains constant
What is a semi conductor
They have higher resistance than metals because they have fewer charge carriers, but some semi-conductors release more charge carriers when their temperature increases, this means resistance is decreased, this means they are excellent sensors.
NTC thermistors
Negative Temperature coefficient thermistor means resistance decreases as temperature increases
Symbol is a rectangle with a line at 45 degrese with a flat bit on the bottom of the rectangle
LDR
This is a light dependant resistor, the grater the intensity of light on the LDR the lower the resistance
Symbol is a rectangle with arrows going towards it
Intensity of light is meaured in LUX
Direction of conventional current
+ to - this is large part of cell/ battery to the small end
What is Kwh
Kilo watt hour to find this so time in hours X kilo watts 1Kwh = 3.6 million joules
What is internal resistance
Inside a battery chemical energy is used to make electrons move, as these electrons move they collide with atoms inside the battery, this collision means battery must have resistance, this is called internal resistance this is why batteries warm up when in use.
What is terminal p.d
The P.d between the terminals on a cell is the terminal p.d, if internal resistance is 0 then the terminal p.d = Vemf
What is lost volts
The energy wasted per coulomb overcoming the internal resistance
How dose conservation of energy affect internal reistance
Energy per coulomb supplied by the source = energy per coulomb used in the load resistance + energy per coulomb wasted in internal resistance
What are the equations for internal resistance
ε = V +v
V= ε -v
ε = I(R+r)
ε = V+Ir
Emf of cells in series
You add the emf of each cell therefore
ε total = ε1+ε2+ε3+…
how to find emf total for cells in parallel
ε total = ε1=ε2=ε3=…
Kirchhoff’s first law
The total current entering a junction = the total current leaving it.
This is the law of conservation of charge, this says that charge is never used up so in a series circuit charge is the same everywhere, charge flows from -ve to +ve small end of battery/cell to big end.
Kirchhoff’s second law.
The total e.m.f. Around a series circuit = the sum of the p.d.s across each component
ε = ΣIR
This is the idea of conservation of energy
Potential divider circuit equations
V1/v2 = R1/R2
AND
Vout = R2/R1+R2 * Vin
What is a potentiometer
It is a potential divider circuit which instead of having the two resistors has one variable resistor which allows you to be able to adjust the voltage output, this is used in speakers to be able to turn the volume up and down.
What is wave length
The length of one full wave, crest to crest or trough to trough.
It is measured in meters
What is amplitude
Amplitude (A) measured in Meters, it is the maximum magnitude of the displacement, which is from displacement of 0 to crest of the wave, or from the displacement 0 to the trough of the wave
What is displacement
Displacement (x) in meters - how far a point on the wave has moved from its undisturbed position
What is period
Period T in seconds - the time taken for a whole wave cycle to complete, one crest and trough.
What is frequency
Frequency (f) in Hertz - the number of cycles per second passing a given point
What is phase
Phase is a measurement of the position of a certain point along the wave cycle
What is phase difference
The amount one wave lags behind another, phase and phase difference are meausred in angles (degrees or radians)
Transverse waves
Vibration is at right angles to the direction of travel, all electromagnetic waves are transverse.
Longitudinal waves
Vibrations are along the direction of travel, these are like sound waves
What is intensity
Intensity is the rate of flow of energy per unit area at right angles to the direction of travel of the wave it has a unit of W/m^2
Intensity = P/A
Intensity is directly proportional to amplitude squared
Facts about electromagnetic waves
1- they all travel at c in a vacuum
2 - they are transverse waves consisting of vibrating electric and magnetic fields, the electric and magnetic fields are at right angles to each other and to the direction of travel
3 - they can be refracted, reflected and diffracted. They all undergo interference they all obey v =fλ
4 - like all progressive waves, progressive EM waves carry energy
5 - EM waves are transverse so, like all transverse waves they can be polarised
Properties of EM spectrum
1 - the longer the wave length, the more obvious the wave characteristics - long radio waves diffract round hills
2 - energy is directly proportional to frequency. Gamma rays have the highest energy; radio waves the lowest.
3 - in general the higher the energy the more dangerous the waves, some are ionising
Radio waves
Wavelength: 10^-1 to 10^6
Penitration: pass through matter
Uses: radio transmission
Microwaves
Wavelength: 10^-3 to 10^-1
Penitration: most pass thought matter but cause heating
Uses: radar, microwave cooking, tv transmission.
Infa-red
Wavelength: 7x10^-7 to 10^-1
Penitration: mostly absorbed by matter, causing heating
Uses: heat detectors, night vision cameras, remote controls, optical fibers
Visible light
Wavelength: 4x10^-7 to 7x10^-7
Penitration: absorbed by matter causing some heating
Uses: human sight, optical fibres
UV
Wavelength: 10^-8 to 4x10^-7
Penitration: absorbed by matter slight innisation
Uses: sunbeds security marks that shows up under UV
X - rays
Wavelength: 10^-13 to 10^-8
Penitration: mostly pass through matter but cause ionisation as they pass.
Uses: to see damaged bones and teeth, airport security scanners, and can be used to kill cancer
Gamma rays
Wavelength: 10^-16 to 10^-10
Penitration: mostly pass through matter but cause ionisation as they pass through
Uses: irradiation of foodsm sterilisation of medical instruments, to kill cancer cells
Strong nuclear force
Acts on hadrons, as you go from 0fm to some more fm you go from repulsive force to a attractive force. Always meausred in femto meters x10-15m
Electrostatic force
Always a repulsive force, more repulsive the closer the two opposite charged objects
Definition of hadrons
Made up of quarks, so proton, nuetron and meason, they are affeced by strong nuclear force
Definition of leptons
They are made of electrons, neutrinos and muons, these are not affected by the strong nuclear force, they are fundamental particles
Fundamental particles
These cannot be Brocken down into smaller parts quarks, electrons…
Weak nuclear force
This is when hadrsons decay with beta decay this force comes into place therefore dose not. Affect leptons.
What are the four forces in nuclius
Weak, strong, electrostatic and gravitational
