Physics - Paper 1

Newton'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