Physics One Day Revision

1
Physics One Day Revision
David Okey
Waves
Mechanics
Nuclear Physics
Electricity
2
Exam

• All questions will be asked in contexts
• Achievement single aspects of phenomena,
  concepts or principles
• Merit will involve reasons
• Excellence reasons and no irrelevancies
• Base Units
• Significant Figures

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Wave Properties

• A amplitude m
• v velocity ms-1
• - wavelength m
• f frequency Hz (waves per second)
• T period c (time for one wave to pass)
• Wave equations

4
Types of waves

• Transverse wave, vibrates perpendicular to
  direction of travel
• eg electromagnetic (light, radio, X-rays etc)
  water waves
• Longitudinal waves, vibrates in same direction as
  wave travels
• eg sound or compression waves
• Link to waves types

5
Supervision of Waves

• Waves can be added together superposition

6
Reflection in curved mirrors

• 2x focal length is radius of curvature
• 2f c
• Drawing ray diagrams
• - parallel to principal axes back thru focus
• - reverse of above
• - travels to pole, reflected at equal angle
• - passes though centre of curvature, reflects
  back along itself
• Images are described as
• Real or virtual
• Upright or inverted
• Magnified or reduced

7
Curved mirrors
d0
so
Ho
f
c
Inverted, real, diminished (reduced) image
8
Ray diagrams in mirrors and lenses

• Use the following formula
• For magnification use the following
• Negative numbers mean virtual images

9
Refraction at a plane boundary

• Refraction occurs as the wave velocity changes in
  different media
• Use formula
• Critical Angle
• When angle of incidence is refracted at 90º

?1
n1 medium 1 less dense v1
n2 medium 2 more dense v2
?2
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Refraction using wave fronts
Wave front -crest
i
Wave has slowed Wavelength is reduced Frequency
same
r
normal
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Waves

• Reflection of waves from a boundary
• wave returns upside down
• Medium of wave changes, then speed of wave
  changes which causes wavelength to change
  Frequency is unchanged
• Eg water waves
• refraction of waves

12
Waves

• Standing wave
• Stationary wave pattern that forms when two waves
  of equal frequency move in opposite directions in
  a medium
• Diffraction
• Bending of a wave as it passes around an edge or
  through a narrow gap
• 2-point source interference

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Electromagnetic waves

• Travel in vacuum
• Constant speed, velocity of light
• (c 3.0 x 108 ms-1)
• Radio/TV
• Microwaves
• Infra red
• Visible light
• Ultra violet
• X-rays
• ?-rays (gamma)

Increasing wavelength low energy
Very short wavelength high energy
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Achievement Criteria

• This standard involves knowledge and
  understanding of
• Motion
• Force
• Momentum, Energy and Power
• You are expected to be able to
• Identify, describe or explain phenomena,
  concepts, relationships or principles.
• Solve problems

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Motion - Linear

Index wf Hong kong NZIP

• Relative motion, change in velocity and vector
  components
• Constant acceleration in a straight line

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Velocity as a Vector
Index wf Hong kong NZIP

• Velocity is a vector
• has direction and magnitude

Velocity of boat relative to water
Velocity of water
Resultant velocity

• velocity of water and boat are components

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Equations of motionKinematic Equations
Index wf Hong kong NZIP

• For use in any situation where there is constant
  acceleration 5 variables

Without d
Without a
Without t
Without vf
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Free Fall under Gravity
Index wf Hong kong NZIP

• Constant acceleration of g10 ms-2 in a downwards
  direction
• use g for falling object
• use -g for object going up

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Projectile Motion
Index wf Hong kong NZIP

• Projectile Motion

Horizontal Velocity Constant
vd/t
Vertical Velocity Gravity Use equations of motion
Horizontal velocity
Vertical velocity
Use trig to find actual velocity and direction
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Force (Unit Newtons)
Index wf Hong kong NZIP

• Components of forces
• Vector addition of forces
• Unbalanced Force causes acceleration
• Fma
• Forces in a spring
• F-kx where F force (N)
• k spring constant (Nm-1)
• x spring extension (m)
• Note -ve indicates x and F in opposite
  directions

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Circular MotionConstant speed with only one
force, Centripetal Force
Index wf Hong kong NZIP

• Centripetal Acceleration
• Torque or turning force
• ? Fd unit is Nm

Centripetal Force
Centrepetal Acceleration
Constant velocity tangent to circle
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Momentum

Index wf Hong kong NZIP

• Momentum, indicates amount of force to change the
  movement of an object
• Impulse the change in momentum
• Symbol p unit kgms-
• Momentum is conserved in collisions
• Momentum can be represented as a vector

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Energy (unit Joules)

Index wf Hong kong NZIP

• Gravitaional Potential Energy
• Energy stored by lifting a height
• Kinetic Energy
• Energy of a moving object, is conserved in
  elastic collisions
• Work Done
• When a force moves an object a distance
• Note Work can also be thought of as the amount
  of energy that has changed form
• Energy stored in a stretched spring

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Power
Index wf Hong kong NZIP

• Amount of energy changing form per second
• Remember that work can be applied to any context
  where energy has changed.

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Models of the Atom

• Dalton 18th Century Chemist, who suggested that
  matter is made from discrete particles
• - atoms
• Thompson discovered electrons then theorized
  nn atom is a sphere of positive charge with
  electrons imbedded
• Plum Pudding model
• Rutherford Student of Thompson, designed an
  experiment to confirm Thompson's model.

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Rutherford's Experiment

Fluorescent screen
Atom diameter
Alpha particle source
Most alpha particles are not deflected by the atom
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Rutherford's Experiment

• Because most alpha particles are not deflected
  Rutherford reasoned that most of an atom is space
• Since some were scattered through large angles
  more than 90? there must
• concentration of mass
• and positive charge
• Rutherford called this a nucleus
• Planetary model of an atom

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Nuclear RadiationParticles emitted in nuclear
decay

• Alpha Particles ?
• Nuclei of Helium atoms
• Heavy slow moving particle 42He2
• Beta Particles ?
• Electron
• Light fast moving particle 0-1 ?
• Gamma Particle ?
• Electromagnetic radiation, very high energy
• ionising radiation

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Radioactive Decay

• When an large atom falls apart to produce
  smaller more stable atoms.
• The atoms give off
• Alpha particles
• Beta particles
• Gamma Particles
• When atoms decay
• The atomic mass (A) is conserved (nucleons)
• The atomic number (Z) or charge is conserved
• Examples

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Half Life

• Each decay is a random event
• In any type of isotope we can predict the time
  for half of the sample to decay
• Called Half Life

Activity
1/2
1/4
Time
T1/2
2T1/2
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Behavior of Sub-Atomic particles in a Magnetic
Field
Magnetic Field
? ve small deviation
x x x x x x x x x x x x x x x x x
x x x x x x x x x x x x x x x x x
x x x x x x x x x x x x x x x x x
x x x x x x x x x x x x x x x x x
x x x x x x x x x x x x x x x x
? No deviation
? -ve large deviation
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Radioactive Decay

• Alpha Particle ?
• Typicaly move at 10 speed of light
• Heavy particle
• Stopped by cm of air or paper
• Beta Particle ?
• Speed up to 90 speed of light
• Light particle
• Travel about 30cm in air stopped by 5mm of
  Aluminium
• Gamma Particle ?
• Speed of light as EM
• No mass
• Penetrates several cm of lead

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Three parts to the course

• Static Electricity
• DC Electricity
• Electromagnetism

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Prior Ideas
Index wf Hong kong NZIP

• Charge - measured in Coulombs
• Electric Current
• Flow of charged particles (usually e-)
• Unit Amps (A) where 1A Cs-1
• Potential Difference (Voltage)
• Unit Volts (V)
• Measured as the energy per unit of charge
• 1V JC-1

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1. Static Electricity
Index wf Hong kong NZIP

• Uniform Electric Field
• Field lines are lines of force
• Field lines are evenly spaced running ? -
• Usually exist between parallel charged plates
• Field strength is calculated from
• unit is NC-1 or Vm-1
• E indicates the strength of an Electric field

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Force on a Charged Particle(in an Electric field)
Index wf Hong kong NZIP

• A charged particle in an electric field (E)
  experiences a force (F)
• Force on a charged particle can be calculated
  from F Eq
• Energy stored by a charged particle in an
  Electric Field
• Note similarity to WFd

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2. DC Electricity
Index wf Hong kong NZIP

• Series Circuits
• Current always the same
• Voltage is divided
• Parallel Circuits
• Current divided
• Voltage is always the same
• Combination Circuits

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Resistance
Index wf Hong kong NZIP

• Series
• Parallel
• Remember that power can be calculated using

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Diodes
Index wf Hong kong NZIP

-
Current direction

• Diodes are called semiconductors
• Diodes only allow current to flow in one
  direction
• Diodes require some energy to function called
  knee voltage
• LED low current device
• light emitting diode

V(V)

I(A)
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Electromagnetism
Index wf Hong kong NZIP

• Force on a charged particle moving in Magnetic
  field (B)
• Right Hand Rule
• FBIL(sin?)

Magnetic Field x
Current
Force/movement
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Induced Voltage and Current
Index wf Hong kong NZIP

• Wire AB (length L) pulled through a magnetic
  field with velocity v
• x x x x
• x x x x
• x x x x
• B becomes ve
• particle experiences a force upwards

A
v
FBqv VBvL
B
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Generator
Index wf Hong kong NZIP

• A generator consists of either-
• A magnet moving in a coil
• A coil moving in a magnetic field
• Induced current can be increased by_
• More turns of wire (loops in coil)
• Stronger magnet
• Movement is faster
• If no current is taken out a voltage still exists
  across the ends of the solenoid