Notes-for-CAIE

Electricity

Electromotive force (EMF): Energy transferred from source per unit charge.

Electric field

Electric field strength: Force per positive charge

DC Circuits

Kirchhoff’s laws

[ˈkɜrkhɔf]

Kirchhoff's 1st law: Sum of currents into a junction IS EQUAL TO Sum of currents out of junction

Kirchhoff’s 1st law is another statement of the law of conservation of charge

Kirchhoff's 2nd law: Sum of e.m.f.s in a closed circuit IS EQUAL TO Sum of potential differences

Kirchhoff’s 2nd law is another statement of the law of conservation of energy

Newton’s laws

Newton's 1st law: If a body is at rest it remains at rest or if it is in motion it moves with a uniform velocity until it is acted on by resultant force or torque

Newton's 2nd law: The rate of change of momentum of a body is proportional to the resultant force and occurs in the direction of force

Newton's 3rd law: if a body A exerts a force on a body B, then body B exerts an equal but opposite force on body A, forming an action-reaction pair

Force

Force: The rate of change of momentum of a body

Deriving a formula for current

I = Anvq
where

• A: cross-sectional area
• n: no. of electrons per unit volume
• v: average drift velocity

Momentum

Use the kinetic model to explain the pressure exerted by gases. [3] s15/22 Q4

• Molecules collide with the wall and there is a change in momentum.
• Change in momentum is force.
• Many of molecular collisions over area provides pressure.

Collision

Elastic collision

Relative speed maintains constant before and after elastic collision K.E. is always conserved

Atoms

Isotope: Nuclei having the same no. of protons [1] but different number of neutrons [1]

Fundamental particles

The Standard model: classifies matter into quarks, leptons and force carriers.

Magnetic fields

• Magnetic flux density: Force per unit length of unit current

Misc

Distance from earth to sun

1.5 EXP 11 meters

Radioactivity

Rutherford’s experiment

Appearance	Inference
**A few** α-particles were deviated through **angles > 90°**	Nucleus is charged and containing the majority of the mass of the atom
**Most** α-particles were deviated through small angles < 10°	The nucleus is very small **in comparison to the atom**

Why Apparatus enclosed in a vacuum [1]

α-particle travels short distance in air

Why β-particle inappropriate for this experiment [2]

• a range of energies
• very small mass
• can be deviated by orbital electrons

Whether isotopes of gold would give rise to different deviations of a particular alpha-particle [2]

• Deviation depends on the charge on the nucleus
• They have the same charge so as to experience same deviation

Decay

Radioactive decay [2]: Nucleus emits α-particles or β-particles or γ-radiation [1] to form a different nucleus [1]

Spontaneous decay [2]: The rate of decay is not affected by external factors [1], like temperature or pressure [1]
Random decay: [1]: Time of decay con’t be predicted / The count rate from a radioactive source fluctuates

β- decay

n -> p + β- + anti-neutrino
udd -> uud + β- + anti-neutrino

β+ decay

p -> n + β+ + neutrino
uud -> udd + β+ + neutrino

Why α-particle lose energy traveling through air

Collision with molecules[1] causes ionisation[1]

Properties of β-radiation [2]

• negatively charged
• speed up to 0.99c
• can be absorbed by 1-4mm of aluminum, or 0.5-2m for ranges in air

Waves

Basic terms

Transverse wave: vibration is perpendicular to wave movemtent

Electromagnetic Waves

v = 3 * 10^8 m/s

λ =

Waves in tubes

n=1, 1st harmonic
n=…

One open

Two open

Interference and Coherence

// Interference: the formation of points of cancellation and reinforcement where 2 coherent waves pass each other

Coherence: waves having a constant phase difference

In phase: 0° / 360° in phase diff Out of phase: 180° in phase diff only

Double-slit Interference

Where  
    a = slit separation  
    D = distance from slit to screen  
    x = fringe width

Diffraction Grating

d sin θ = nλ

Where d = distance between successive slits
        = reciprocal of number of lines per meter
      θ = angle from horizontal equilibrium
      n = order number
      λ = wavelength