Studied by 0 peopleNewton's Third Law
If object A exerts a force on object B, then object B exerts an equal but opposite force on object A
Newton's Third Law pairs
Example: An object exerts a weight of 50N onto the earth. The third law pair would be that the earth would exert a NCF of 50N on the object
Conditions for Newton's Third Law Pairs to be true
Two Different Forces
Act on the same line
Same magnitude
Different objects
same time
Potential Divider equation
Vout/Vin = R1/R1+R2
Potential Dividers and thermistors
If a thermistor is used as R1, as temperature decreases resistance increases and thus Vout increases as they are proportional, this can be used as a heating system to turn it on if it gets cold enough
Potential Dividers and LDRs
If a LDR is used as R1, as light decreases resistance increases and thus Vout increases as they are proportional, this can be used for street lights to be turned on as light decreases
Thermistor
a resistor whose resistance depends on the temperature of the thermistor
As temperature decreases resistance increases
LDR
Light dependent resistor
As light increases resistance decreases
Rheostat
When a variable resistor is used to control current
Variable Resistor
A resistor whose value can be varied between its minimum and maximum values.
Variable Resistors and Potential Divider Uses
A variable resistor can act as a potential divider to act as a continuous slider to increases or decrease Vout. This can be used as a dimmer switch
Magnetic Flux Density
a measure of the strength of the magnetic field.
How densely packed lines of flux are equates to how strong a field is
Measures in Tesla T
Magnetic Flux
The total number magnetic field lines that pass through a surface
= magnetic flux density x Area
Magnetic Flux Linkage
The product of the magnetic flux and the number of turns in a given coil = Number of coils x magnetic flux
Equations of motion
v = u + at
s = 1/2(v+u)t
s = ut + 1/2at^2
v^2 = u^2 + 2as
Equation of motion for velocity
v = u + at
Equation of motion for distance
s = 1/2(v+u)t
s = ut + 1/2at^2
Equation of motion for velocity squared
v^2 = u^2 + 2as
Equation for an magnetic field on a wire
F = BIL
F = Force, B = Magnetic field strength (density), I = Current, L = Length
Equation for a magnetic field on a wire not at 90 degrees to the field
F = BILsin(angle)
Angle at 90 degrees should just use F = BIL as sin90 = 1 therefore cos component will not affect the force
Angle at 90 degrees should just use F = BIL as sin90 = 1 therefore cos component will not affect the force
Equation for a magnetic field on a moving charge
F = BQV
F = Force, B = Magnetic field strength (density), Q = charge, V = velocity
Equation for a magnetic field of a moving charge not at 90 degrees to the field
F = BQVsin(angle)
Angle at 90 degrees should just use F = BIL as sin90 = 1 therefore cos component will not affect the force
Angle at 0 degrees will be 0 as sin0 = 0
Fleming's Left Hand Rule
First Finger = Field
seCond finger = Current
thuMb = Motion
Relativistic Effects
Only when objects approach the speed of light do our observations begin to depart measurably from the predictions of Newtonian Physics
Muon Decay and Relativistic Effects
Muons are created a few kilometers above the earth yet for the time they should take to get here they would decay before they hit the surface
But they do hit the surface, this is due to relativistic effects as muons are going close to the speed of light
The doppler Effect Model Answer
As something that is moving is giving out a wave its frequency can change as it is being compressed by the moving object and therefore to a relative observer the frequency appears higher
Cosmological Red Shift Model Answer
As the universe expands, galaxies are moving away from us the relative observer. The light these galaxies give off it also redshifted so that its wavelength increases
Cosmological Redshift Equation
z = ∆Wavelength/Wavelength = Velocity/Speed of light
Total Internal Reflection Model Answer
If the angle of incidence is greater than the critical angle no light is refracted out of the medium and all of the light is reflected back into the medium. All light has been totally internally reflected
Critical Angle
The largest angle as which refraction out of a denser medium is possible
Critical Angle Equation
n = 1/sinc
n = Refractive Index, c = critical angle
How to measure the refractive index of a material?
Measure the angle of incidence of a light ray in a material and then the angle of refraction
use sin1/sinr = n to find the refractive index
How to predict whether total internal reflection will happen?
If the angle of incidence as it meets the surface is less than the critical angle, the ray will be refracted into the medium, but some can get reflected, this is know as partial internal reflection
Increasing this will go to total internal reflection.
How to add vector components?
Use a protractor to ensure correct angle
Place each vector head to tail
Join the first tail and final head together to get the resultant
Resolving vectors
Place vectors together
For a right angle triangle sides can be calculated using Pythagoras
Other triangles can be calculated using cosine
Internal Resistance
resistance inside the source of electrical energy - loss of PD per unit current in the source when current passes through it
Electromotive force
The electrical potential energy transferred from other forms, per coulomb of change that passes through the source
Energy transfer EMF equation
Work Done = Charge x emf
Emf Equations
E = V + IR
E = IR + Ir
E = I(R + r)
(E = emf, V = Voltage, I = Current, R = resistance)
Lost Volts
The potential difference across the internal resistor of a source of e.m.f.
emf = V + lost volts
The difference between emf and pd
emf is the energy transferred from chemical to electrical
pd is the energy transferred from electrical to other forms e.g. light, heat
emf is transfered from other forms where as pd transfers to other forms
How to increase induced emf
Use a stronger magnet
use a coil with more turns
use a coil with greater cross sectional area
Make relative movement between magnet and conductor faster
Baryon
A hadron consisting of three quarks
Meson
A hadron consisting of a quark and an antiquark
Lepton
An elementary particle that have no internal structre
Hadron
A particle made up of quarks
Lepton Examples
1st gen electron
2nd gen muon
3rd gen tau
Increasing 1-3
Examples of mesons
pion, kaon
Examples of baryons
protons and neutrons
An object thrown off a cliff time taken to reach ground
Use suvat remembering u is 0
An object thrown off a cliff distance it lands from the foot of the cliff
Horizontal distance = horizontal velocity x time of flight
Horizontal velocity is given
Time may be given or worked out earlier using suvat
An object thrown off a cliff magnitude of final velocity
Vertical Velocity = u + at
Horizontal Velocity is given in the question
Use Pythagoras to find resultant
An object being hit off the ground at an angle time in air
Consider vertical velocity = 0
Consider vertical component of initial launch
using SOHCAHTOA
Know acceleration is negative and dependant on the planet
Use suvant to find t
Double it as this motion is parabolic and thus half of the time
An object being hit off the ground at an angle horizontal distance travelled
Work out horizontal component of inital velocity
Use d = horizontal velocity x time
Effect of friction on projectiles vertical motion
Upwards gravity and friction work together to slow down projectile
Downwards friction goes against gravity slowing it
Effect of friction on projectiles horizontal motion
Drag forces oppose the motion, leading to horizontal deceleration
Change in resistance with temperature model answer
Metals contain large numbers of free electrons
As these electrons move through the metal lattice they collide with vibrating metal ions
These collisions oppose the flow of electrons so the metal has a set resistance
When temperature increases ions vibrate faster and make it more difficult for electrons to pass through the lattice increasing resistance futher
Faraday's Law
The magnitude of the induced emf is directly proportional to the rate of change of flux linkage
Faraday's Equation
emf = coils x change in flux linakge / time taken
Change in flux linkage can be calculated by multiplying the field strength and the area
Lenz's Law
The direction of an induced current is such that it will try to oppose the change in flux that is producing it
Lenz's Equation
Is like faraday's but adds a negative sign
emf = -coils x change in flux linakge / time taken
An emf is induced
When there is relative movement between a magnet and a coil
Dropping a bar magnet through a coil
As the magnet enter the coil the flux linkage of the coil increases and an emf is induced
As the magnet falls right in the middle of the coil there is 0 flux linkage and no emf induced
As the magnet falls out of the coil the flux linkage decreases and emf is induced in the opposite direction
Emf is equal to a area strip under the graph
The second dip is narrower as the magnet is accelerating due to gravity
Note
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