# Unit 4 definitions

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Momentum
Mass x velocity
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Principle of conservation of momentum
Momentum is conserved in all interactions where no external force acts
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Newton’s 2nd law of motion
The rate of change of momentum of a body is directly proportional to the resultant force acting on it
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Elastic collision
Total kinetic energy before the collision = the total kinetic energy after the collision
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Inelastic collision
Total kinetic energy before the collision is greater than the total kinetic energy after the collision (some kinetic energy is transferred into other forms during the collision)
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Magnetic field
Region of space around a magnet where it exerts magnetic forces
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Catapult field
The magnetic field of the magnet exerts a force on the magnetic field of the current carrying conductor. The direction of the force is given by FLHR
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Magnetic flux
Magnetic flux density x area of coil
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Magnetic flux linkage
Magnetic flux through coil x number of turns of the coil
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Faraday’s law
the induced e.m.f. across the ends of a conductor is directly proportional to the rate of change of magnetic flux the conductor experiences
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Lenz’s law
The direction of the induced e.m.f. is such that it tends to oppose the flux change causing it, and does oppose it if an induced current flows
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Eddy current
Current induced in the soft iron core of a transformer due to the changing magnetic flux in the core
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Capacitance
Charge stored on the plates of a capacitor when a p.d. of 1 volt is applied. (charge / p.d.)
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Time constant
Time taken for the charge on a capacitor to drop to 1/e of its original value (R x C)
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Exponential
A change where the property (charge) changes by a constant ratio in a fixed time interval
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Electric field
A region of space in which a charged object experiences an electric force
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Electric field strength
Force on a 1 coulomb charge in an electric field (force/charge)
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Potential gradient
Potential difference/distance (the rate at which potential changes with distance)
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Thermionic emission
Escape of electrons from the surface of a metal when they are supplied with thermal energy
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Fundamental particle
A particle that cannot be broken up into smaller constituents
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Standard model of particle physics
A theory which identifies 12 fundamental particles from which all matter is made and four fundamental forces that govern reactions between the particles
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Quark
A group of fundamental particles of which the proton and neutron are made
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Lepton
A group of fundamental particles of which the electron is one
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Generation
Family (particles in one generation have a family resemblance to particles in the other generations)
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Fundamental force
A force that cannot be explained in terms of any other force
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Strong nuclear force
A fundamental force that acts on all quarks
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Weak nuclear force
A fundamental force that acts on quarks and leptons and controls beta decay
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Neutrino
A fundamental particle of no charge and negligible mass released during beta decay
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Hadron
Particle made of quarks
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Baryon
Particle made of three quarks
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Meson
Particle made of a quark and an anti-quark
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Antimatter
Has same mass as its matter particle and opposite charge. Annihilates readily with matter
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Positron
Antimatter particle of the electron
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Annihilation
The conversion of mass into energy when matter and antimatter meet
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Inverse square law
The force is inversely proportional to the square of the preparation between two charges
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Coulomb’s law
The force is directly proportional to the product of the charges divided by the square of the separation
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De Broglie wavelength
Planck constant divided by momentum
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Rest mass
Mass of an object when it is at rest
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Rest mass energy
Energy needed to create a particle at rest from nothing
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Linear accelerator
A particle accelerator using an electric field to accelerate particles in a straight line
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Cyclotron
A particle accelerator using magnetic fields to make charged particles move in a circular path
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Centripetal force
Resultant force acting towards the centre of the circle for any body moving with circular motion
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Angular velocity
Angle moved through in radians per second
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Time Period
Time taken for one complete oscillation
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Centripetal acceleration
Acceleration towards the centre of the circle for any body moving at constant speed with circular motion
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## Other cards in this set

### Card 2

#### Front

Momentum is conserved in all interactions where no external force acts

#### Back

Principle of conservation of momentum

### Card 3

#### Front

The rate of change of momentum of a body is directly proportional to the resultant force acting on it

### Card 4

#### Front

Total kinetic energy before the collision = the total kinetic energy after the collision

### Card 5

#### Front

Total kinetic energy before the collision is greater than the total kinetic energy after the collision (some kinetic energy is transferred into other forms during the collision)

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