# Unit 4 definitions

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- Created by: Rebecca Neal
- Created on: 05-02-14 12:16

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

#### Back

### Card 4

#### Front

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

#### Back

### 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)

#### Back

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